HomeMy WebLinkAbout4 Stanley Lot 2A Drainage Report Sep 29 2025 (1)1
PRELIMINARY DRAINAGE REPORT
Freelan Heights at The Stanley Townhomes
Stanley Historic District Lot 2A
Overlook Court
Estes Park, CO
Issue Date:
September 29, 2025
Prepared By:
Van Horn Engineering and Surveying Inc.
1043 Fish Creek Road
Estes Park, Colorado 80517
VAN HORN ENGINEERING AND SURVEYING
LAND SURVEYS
SUBDIVISIONS
DEVELOPMENT PLANNING
IMPROVEMENT PLATS
STRUCTURAL ENGINEERING
SANITARY ENGINEERING
MUNICIPAL ENGINEERING
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I hereby certify that this preliminary report (plan) for the Preliminary Drainage Design
for Freelan Heights at The Stanley Townhomes was prepared by me (or under my direct
supervision) for the owners thereof and meets or exceeds the criteria in the Larimer
County Stormwater Design Standards.
__________________________
Frank E. Roberts
Licensed Professional Engineer #39508, State of Colorado
For Van Horn Engineering and Surveying Inc.
9/29/2025
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Table of Contents
1. SCOPE ........................................................................................................................ 4
2. PROJECT DESCRIPTION ......................................................................................... 5
3. BASIN DESCRIPTIONS ........................................................................................... 6
4. DESIGN METHODS AND ASSUMPTIONS ........................................................... 9
5. RECOMMENDATIONS .......................................................................................... 10
Attachments
x Historic and Post-Developed Drainage Basin Delineation Plans
x USDA Soils Survey Data
x Rainfall Data
x Preliminary Drainage Calculations
x Previous Drainage Reports
o “Overlook Subdivision/Stanley Hotel Drainage Analysis/Report”
by Van Horn Engineering & Surveying, Inc., signed April, 28,
2014
o “Storm-Water Management Plan Overlook Subdivision” by
Cornerstone Engineering & Surveying, Inc., signed May 23, 2003
o “Final Drainage Report – Grand Heritage Hotel – Aspire Wellness
Complex at the Stanley-Phase 1 – Amended Plat of Lot 4, Stanley
Historic District” by Van Horn Engineering & Surveying, Inc.,
signed on May 19, 2015
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1. SCOPE
This report is a drainage analysis for Freelan Heights at The Stanley Townhomes
project. The overall infrastructure for the storm water system is currently installed and
was originally designed in 2003 as part of the Overlook Condominium project and was
subsequently recommended to be upgraded after a re-analysis effort in 2014. Most of the
recommended upgrades were offsite in relation to the Freelan Heights project. This
report is intended to describe the storm water system already in place and to describe any
necessary upgrades to the system that are required due to slight differences from the
original design assumptions regarding the final development. This report is intended to
focus only on the stormwater system components that are affected by the Freelan Heights
project and is not intended to revisit other drainage items within the Overlook
Condominium or the Stanley Historic District properties, nor is it intended to provide
verification that previous upgrades as recommended in the 2014 report were implemented
offsite. Included within the report is an overall preliminary drainage analysis containing
the following:
1. Description of the drainage basins for both the project site and offsite areas as
applicable.
2. Peak runoff rates for both the historic (undeveloped) and post development
conditions.
3. Recommendations/verifications for the existing storm water drainage system and
additional features required for the proposed development.
4. Previous drainage studies for the Overlook Subdivision and/or related to
downstream detention assumptions: A. “Overlook Subdivision/Stanley Hotel
Drainage Analysis/Report” by Van Horn Engineering & Surveying, Inc., signed
April, 28, 2014, which includes provisions for development on Stanley Lot 2A as
part of a re-analysis of the original drainage report for the Overlook
Condominiums. B. “Storm-Water Management Plan Overlook Subdivision” by
Cornerstone Engineering & Surveying, Inc., signed May 23, 2003, which is the
original drainage report for the Overlook Condominium development. C. “Final
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Drainage Report – Grand Heritage Hotel – Aspire Wellness Complex at the
Stanley-Phase 1 – Amended Plat of Lot 4, Stanley Historic District” by Van Horn
Engineering & Surveying, Inc., signed on May 19, 2015, which details
downstream detention for a portion of the eastern side of this project site.
2. PROJECT DESCRIPTION
Freelan Heights at The Stanley Townhomes is a proposed 10 lot townhome
subdivision of Lot 2A, Amended Lot 2, Final Plat Lots 1 and 2, Stanley Historic District,
which is an existing 3.09 acre parcel within the Town of Estes Park, and is located in the
North ½ of the Southeast ¼ of Section 24, Township 5 North, Range 73 West of the 6th
P.M. Applicable storm drainage manuals are the Larimer County Stormwater Design
Standards and the Mile High Flood District Urban Storm Drainage Criteria Manual.
The project site currently includes mostly undeveloped terrain with a paved road
starting at the Overlook Court cul-de-sac that extends to the northwest where it intersects
a gravel fire access road that connects to the adjacent property to the northwest. From
this point the paved road curves east and will provide access to the new upper lots. The
property has a large rock outcropping at the western portion of the property which is not
part of the buildable area. The proposed use of the property will be for a total of 10
single family residential units each on a separate lot. The proposed subdivision is
bounded on the north by Black Canyon Resort property, Ridgeview Condos, and
residential homes accessed from Prospector Lane. The proposed subdivision is bounded
on the southeast by the Overlook Condos and on the southwest by the Stanley property.
The property is located in a Zone X-Un-shaded classification according to the Federal
Emergency Management Agency (FEMA) FIRM Maps. The slope of the existing
buildable portion of the property is generally sloping downhill from north to south at
approximate grades on the order of 10%-20%. The overall drainage basin draining
through and from the site includes this proposed subdivision area (on-site flow) plus a
small portion of the properties to the north (off-site flow). The overall drainage basin is
split into several smaller sub-basins in accordance with the most recent drainage report
for this area which is the Van Horn Engineering drainage report dated April 28, 2014.
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Utilities including sewer, water, electric, communications, and storm water
facilities are largely in place as infrastructure mains were constructed in conjunction with
the Overlook Subdivision. Service lines will be extended to individual lots as necessary.
Driveways and access roads will be installed and extended as shown on the project plans.
3. BASIN DESCRIPTIONS
EXISTING CONDITIONS
The most recent drainage report for this project area (by VHE, dated 4/28/2014)
will be utilized for historic, pre-development discharge rates for storm water flows.
Historic drainage basins were delineated as part of that report and a description of the
method to delineate the basins is contained in the previous report on page 13. Six
existing conditions basins were delineated in the vicinity of this property as part of the
previous report (reference Section 3 of the previous report’s appendix for the pre-
development basin map as well as this report’s attachments): basin A, basin B-1, basin
B-2, basin C-1, basin C-2, and basin C-3. As determined as part of the previous drainage
report, existing conditions basin delineations, hydrologic properties for each basin (area
and runoff coefficients), historic release rates, and historic release locations are all shown
on the pre-development conditions detention sizing drainage basins exhibit. This pre-
development drainage basin plan was also re-created specific to this project area and is
attached to the report. Basin identifiers and characteristics were maintained to match the
2014 drainage report. The basins specific to this project area include four of the six
basins delineated in the previous report. Basins A, B-1, B-2, and C-3 have area within
the project site.
Basin A is at the southwest corner of the site and consists of 0.10 acres with
coverage consisting of a steep rock outcropping at the north end and mixed open meadow
area with juniper and ponderosa pine trees at the south end of the basin. This area
currently free drains offsite in the southern direction.
Basin B-1 is located to the northwest and adjacent to Basin A at the southwest
portion of the project site. Basin B-1 is similar to Basin A in ground cover
characteristics, a rock outcropping to the north and mixed open meadow area with juniper
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and ponderosa pine trees at the south end of the basin. Basin B-1 is 0.35 acres in size and
free drains offsite to the south.
Basin B-2 is the largest of the four basins on the property with a size of 2.76 acres
including some offsite tributary area from neighboring properties to the north and
northwest. The ground cover for Basin B-2 consists of the large rock outcropping at the
northwest portion of the basin, existing improvements, including the gravel access road
and portions of three buildings on the property to the north, and the Outlook Court cul-
de-sac. The remainder of Basin B-2 is undeveloped mixed open meadow area with
juniper and ponderosa pine trees, the existing grade slopes to the south. Stormwater
runoff from Basin B-2 currently drains to an existing stormwater detention pond which is
located partially on the south end of the property. A portion of the existing detention
pond is located on the property to the south within a drainage easement. There is a
natural high point at the east end of the Overlook Court cul-de-sac which also splits
drainage basin B-2 and C-3. Drainage to the west of this high point naturally drains
southwest and remains in basin B-2. This includes street drainage from the Overlook
Court cul-de-sac which is currently collected in a curb inlet type R drain basin which
discharges via an existing 12” diameter ADS pipe slightly downslope and to the
southwest of the type R. Stormwater discharge from the existing 12” diameter pipe is
conveyed through a ditch the remainder of the way to the existing detention pond
described above.
Basin C-3 overlaps the eastern portion of the site with an overlap area equal to
0.76 acres and this area is east of the natural high point described above. Basin C-3 has a
total area of 10.73 acres according to the 2014 drainage report. The portion of the site
located within basin C-3 is open meadow area and slopes to the south in the direction of
Overlook Court. Stormwater from this drainage basin currently sheet drains to the south
and southeast over the curb and into the roadside gutter along Overlook Court which
slopes to the east and eventually south to an existing detention basin located at the
southeast corner of the Overlook Condominium property.
DEVELOPED CONDITIONS
The same four drainage basins are outlined for this project’s developed conditions
as were described for the pre-developed conditions, basins A, B-1, B-2, and C-3.
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Basin A will remain as-is with no development within the basin. This basin will
continue to free discharge to the south off property. Consideration for this free discharge
will be accounted for in the overall site detention calculations. This basin has a natural
percent impervious value equal to 51% due to the overlap with the large rock formation
to the west.
Basin B-1 will contain some permanent developed features planned for this
project. A portion of two houses and a small portion of driveway are planned to be
constructed within basin B-1. The resulting impervious coverage is on the order of 63%
for the proposed conditions within basin B-1 which also takes into account the large rock
formation to the west. This basin will continue to free discharge to the south off
property. Consideration for this free discharge will be accounted for in the overall site
detention calculations.
Basin B-2 will contain a lot of the developed features that are planned for this
project. Proposed developed coverage will include homes, paved access roads, and pave
driveways. The resulting impervious coverage has been calculated to be 48%. This basin
is planned to discharge directly to the existing detention basin as it does now. The
resulting developed discharge rate vs. the historic discharge rate will be discussed later in
this report. As part of the final drainage report, the existing type R and existing 12”
diameter discharge pipe will be checked for adequate capacity in conjunction with any
anticipated increased inflow.
Management of stormwater generated from the overlapping area of Basin C-3
with the property is proposed to continue to function as it currently does, which entails
sheet flow across the new lots with drainage over the back of the existing curb and into
the existing road side gutter along Overlook Court. The calculated developed impervious
coverage for this basin as a result of the planned improvements is equal to 28%. For on-
site detention facility calculations for the Aspire Wellness Complex for which basin C-3
is tributary to, the assumed impervious coverage was 40% for the upstream offsite
drainage basin (OS4) which includes this area of drainage basin C-3. This calculation
was part of the 2015 drainage report prepared by VHE and is for detention sizing for a
project downstream of the Overlook Condos. In addition, developed conditions
stormwater runoff from this project’s overlap with basin C-3 was accounted for in the
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detention sizing of the detention basin located at the southeast corner of the Overlook
Condominiums and this was presented in the 2014 drainage report prepared by VHE.
The impervious coverage for basin C-3 in the 2014 drainage report was assumed to be
51% for detention sizing.
4. DESIGN METHODS AND ASSUMPTIONS
The most important aspect of this drainage analysis is to re-calculate the
stormwater discharges from each basin taking into account this project’s proposed
improvements for comparison to the assumptions that were made previously regarding
developed conditions for this property as part of the previous drainage studies. The 2014
drainage study utilized a weighted runoff coefficient calculation (“c” value) based on
typical “c” values representative of different ground cover and the rational method to
calculate peak runoff for each drainage basin. This method was also utilized to calculate
new peak runoff for the proposed conditions for each drainage basin. In addition, peak
discharges were calculated using the Urban Storm Drainage Criteria Manual (USDCM)
methodology for peak runoff. This method is based on “c” value equations which take
into account the NRCS soil group (Type D for this project site), storm return period, and
percent imperviousness. Discharge is further calculated with the rational method after
taking into account the total time of concentration for runoff within the basin. Peak
discharges from both of these “c” value calculation methods were compared and the most
conservative (largest) value utilized for detention requirement calculations.
As previously mentioned, in conjunction with the final drainage report, the
existing type R inlet and existing 12” diameter discharge pipe located at the southwest
corner of the Overlook Court cul-de-sac will be checked for adequate capacity in
conjunction with any anticipated increased inflow. The Manning’s equation will be
utilized for calculation of flow in pipes with an appropriate surface roughness (N value)
and pipe slope. Drainage swale capacities as applicable will be calculated by Manning’s
equation for open channel flow. Curb and inlet capacities will be verified as appropriate.
Storm water detention is currently in place which was sized in the 2014 drainage
report and took into consideration future development on this property. As described
previously, verification of the implications of the actual proposed improvements vs. the
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assumptions that were made for future improvements are important to ensure historic
(pre-development) discharge rates are maintained. Historic discharge rates were
calculated previously in the 2014 drainage report for the Overlook Condominium project
based on pre-development conditions for that project. Those are the historic discharge
rates that will be maintained. Drainage will be detained and released at a rate that
compensates for the small areas that will free flow offsite (basins A and B-1) in the
developed condition to maintain historic release rates at specific conveyance features (the
outlets of the existing detention ponds) and as an overall site.
5. RECOMMENDATIONS
Calculations completed as part of the 2014 drainage study indicate the historic
existing conditions total runoff generated from the western portion of the site in the minor
(10 year) and major (100 year) storm event is 4.59 cubic feet per second (cfs) and 9.45
cfs respectively which includes basins A, B-1, and B-2. These values represent the sum
of historic drainage basins A, B-1, and B-2. Calculations as part of this drainage report
indicate the proposed conditions total storm water runoff generated from the western
portion of the site in the minor and major storm event is 7.12 cfs and 15.29 cfs
respectively. These values represent the sum of proposed drainage basins A, B-1, and B-
2 but these values are not the discharge rates from the site as detention is in place to slow
release rates to historic values (9.45 cfs for the major storm event). When considering
the free release of developed drainage basins A & B-1 the allowable release rate for the
detention pond is 6.88 cfs for the major storm event to achieve the historic discharge for
the western portion of the overall site overall site (basins A, B-1, and B-2). The detention
pond infill rate is 12.72 cfs generated from developed drainage basin B-2. These infill
and outlet rates indicate a need for 4 cubic feet of storage volume. The pond indicated on
the preliminary plans provides approximately 4,157 cubic feet of storage volume. The
2014 drainage report indicated a required storage volume of 4,033 cubic feet. The actual
as-built detention pond capacity will be verified and the pond will be enlarged as part of
this project as found necessary after the as-built survey. There is room to expand the
pond in footprint and vertical elevation if found necessary.
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Regarding the eastern portion of the property located in drainage base C-3, and
outlined previously in this report, it has been concluded based on verification of this
project’s proposed 28% developed impervious cover that adequate downstream
conveyance and detention has been accounted for both as part of the 2014 drainage report
which re-analyzed the Overlook Condo project storm water plan (including the Freelan
Heights property) and the 2015 drainage report which sized detention for the downstream
Aspire Wellness Center while taking into account developed upstream conditions within
offsite drainage basin OS4 (includes basin C-3). 40% and 51% impervious coverage was
assumed for drainage basin C-3 in the 2014 and 2015 drainage reports, respectively,
which are both less than the proposed 28% coverage on the portion of the Freelan
Heights project within drainage basin C-3.
As mentioned previously, other storm existing water facilities that will be verified
as part of the final drainage report include the type R inlet and the associated 12”
diameter discharge pipe, as well as curb and gutter as appropriate. Additional detention
pond features will include the controlled discharge outlet structure and water quality
features (pond bottom filter media).
This report uses theoretical hydrologic rainfall information for statistical rainfall
events in this area. Storm events and all “acts of God” can be unpredictable. All on-site
conveyance measures have been included to guard against damage from a statistical “100
year” event. Ongoing maintenance and inspection of the installed features will be critical
in order to keep the system working properly.
Furthermore this drainage analysis utilized industry accepted formulas and
methods to estimate peak runoff values for the historic (undeveloped) and developed
conditions. Peak discharge exiting the property is limited to historic values and at
historic locations. Downstream conveyance of historic stormwater flows is assumed to
be in place as it is the responsibility of each landowner to allow for historic
(undeveloped) flow through their property generated from properties upstream at the
historic flow path and their responsibility to make appropriate accommodations for this
flow if historic flow paths are altered by them on their property.
HISTORIC AND POST-
DEVELOPED DRAINAGE BASIN
DELINEATION PLANS
0.58
0.72
0.57
0.72
0.47
0.58
USDA SOILS SURVEY DATA
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Estes Park Area, Colorado,
Parts of Boulder and
Larimer Counties
Natural
Resources
Conservation
Service
September 26, 2025
Preface
Soil surveys contain information that affects land use planning in survey areas.
They highlight soil limitations that affect various land uses and provide information
about the properties of the soils in the survey areas. Soil surveys are designed for
many different users, including farmers, ranchers, foresters, agronomists, urban
planners, community officials, engineers, developers, builders, and home buyers.
Also, conservationists, teachers, students, and specialists in recreation, waste
disposal, and pollution control can use the surveys to help them understand,
protect, or enhance the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil
properties that are used in making various land use or land treatment decisions.
The information is intended to help the land users identify and reduce the effects of
soil limitations on various land uses. The landowner or user is responsible for
identifying and complying with existing laws and regulations.
Although soil survey information can be used for general farm, local, and wider area
planning, onsite investigation is needed to supplement this information in some
cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/
portal/nrcs/main/soils/health/) and certain conservation and engineering
applications. For more detailed information, contact your local USDA Service Center
(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil
Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?
cid=nrcs142p2_053951).
Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads. Clayey or wet soils are poorly suited to use as
septic tank absorption fields. A high water table makes a soil poorly suited to
basements or underground installations.
The National Cooperative Soil Survey is a joint effort of the United States
Department of Agriculture and other Federal agencies, State agencies including the
Agricultural Experiment Stations, and local agencies. The Natural Resources
Conservation Service (NRCS) has leadership for the Federal part of the National
Cooperative Soil Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Web Soil Survey, the site for official soil survey information.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
programs and activities on the basis of race, color, national origin, age, disability,
and where applicable, sex, marital status, familial status, parental status, religion,
sexual orientation, genetic information, political beliefs, reprisal, or because all or a
part of an individual's income is derived from any public assistance program. (Not
all prohibited bases apply to all programs.) Persons with disabilities who require
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alternative means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice
and TDD). To file a complaint of discrimination, write to USDA, Director, Office of
Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or
call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity
provider and employer.
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Contents
Preface....................................................................................................................2
How Soil Surveys Are Made..................................................................................5
Soil Map..................................................................................................................8
Soil Map................................................................................................................9
Legend................................................................................................................10
Map Unit Legend................................................................................................12
Map Unit Descriptions........................................................................................12
Estes Park Area, Colorado, Parts of Boulder and Larimer Counties..............14
32—Rock outcrop-Cathedral complex, 20 to 100 percent slopes...............14
50—Cathedral-Ratake complex, 5 to 15 percent slopes.............................15
References............................................................................................................18
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How Soil Surveys Are Made
Soil surveys are made to provide information about the soils and miscellaneous
areas in a specific area. They include a description of the soils and miscellaneous
areas and their location on the landscape and tables that show soil properties and
limitations affecting various uses. Soil scientists observed the steepness, length,
and shape of the slopes; the general pattern of drainage; the kinds of crops and
native plants; and the kinds of bedrock. They observed and described many soil
profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The
profile extends from the surface down into the unconsolidated material in which the
soil formed or from the surface down to bedrock. The unconsolidated material is
devoid of roots and other living organisms and has not been changed by other
biological activity.
Currently, soils are mapped according to the boundaries of major land resource
areas (MLRAs). MLRAs are geographically associated land resource units that
share common characteristics related to physiography, geology, climate, water
resources, soils, biological resources, and land uses (USDA, 2006). Soil survey
areas typically consist of parts of one or more MLRA.
The soils and miscellaneous areas in a survey area occur in an orderly pattern that
is related to the geology, landforms, relief, climate, and natural vegetation of the
area. Each kind of soil and miscellaneous area is associated with a particular kind
of landform or with a segment of the landform. By observing the soils and
miscellaneous areas in the survey area and relating their position to specific
segments of the landform, a soil scientist develops a concept, or model, of how they
were formed. Thus, during mapping, this model enables the soil scientist to predict
with a considerable degree of accuracy the kind of soil or miscellaneous area at a
specific location on the landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil
scientists must determine the boundaries between the soils. They can observe only
a limited number of soil profiles. Nevertheless, these observations, supplemented
by an understanding of the soil-vegetation-landscape relationship, are sufficient to
verify predictions of the kinds of soil in an area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other features that enable them
to identify soils. After describing the soils in the survey area and determining their
properties, the soil scientists assigned the soils to taxonomic classes (units).
Taxonomic classes are concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes are used as a basis for
comparison to classify soils systematically. Soil taxonomy, the system of taxonomic
classification used in the United States, is based mainly on the kind and character
of soil properties and the arrangement of horizons within the profile. After the soil
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scientists classified and named the soils in the survey area, they compared the
individual soils with similar soils in the same taxonomic class in other areas so that
they could confirm data and assemble additional data based on experience and
research.
The objective of soil mapping is not to delineate pure map unit components; the
objective is to separate the landscape into landforms or landform segments that
have similar use and management requirements. Each map unit is defined by a
unique combination of soil components and/or miscellaneous areas in predictable
proportions. Some components may be highly contrasting to the other components
of the map unit. The presence of minor components in a map unit in no way
diminishes the usefulness or accuracy of the data. The delineation of such
landforms and landform segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, onsite
investigation is needed to define and locate the soils and miscellaneous areas.
Soil scientists make many field observations in the process of producing a soil map.
The frequency of observation is dependent upon several factors, including scale of
mapping, intensity of mapping, design of map units, complexity of the landscape,
and experience of the soil scientist. Observations are made to test and refine the
soil-landscape model and predictions and to verify the classification of the soils at
specific locations. Once the soil-landscape model is refined, a significantly smaller
number of measurements of individual soil properties are made and recorded.
These measurements may include field measurements, such as those for color,
depth to bedrock, and texture, and laboratory measurements, such as those for
content of sand, silt, clay, salt, and other components. Properties of each soil
typically vary from one point to another across the landscape.
Observations for map unit components are aggregated to develop ranges of
characteristics for the components. The aggregated values are presented. Direct
measurements do not exist for every property presented for every map unit
component. Values for some properties are estimated from combinations of other
properties.
While a soil survey is in progress, samples of some of the soils in the area generally
are collected for laboratory analyses and for engineering tests. Soil scientists
interpret the data from these analyses and tests as well as the field-observed
characteristics and the soil properties to determine the expected behavior of the
soils under different uses. Interpretations for all of the soils are field tested through
observation of the soils in different uses and under different levels of management.
Some interpretations are modified to fit local conditions, and some new
interpretations are developed to meet local needs. Data are assembled from other
sources, such as research information, production records, and field experience of
specialists. For example, data on crop yields under defined levels of management
are assembled from farm records and from field or plot experiments on the same
kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on
such variables as climate and biological activity. Soil conditions are predictable over
long periods of time, but they are not predictable from year to year. For example,
soil scientists can predict with a fairly high degree of accuracy that a given soil will
have a high water table within certain depths in most years, but they cannot predict
that a high water table will always be at a specific level in the soil on a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies on aerial photographs and
Custom Soil Resource Report
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identified each as a specific map unit. Aerial photographs show trees, buildings,
fields, roads, and rivers, all of which help in locating boundaries accurately.
Custom Soil Resource Report
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Soil Map
The soil map section includes the soil map for the defined area of interest, a list of
soil map units on the map and extent of each map unit, and cartographic symbols
displayed on the map. Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
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Custom Soil Resource Report
Soil Map
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455770 455790 455810 455830 455850 455870 455890 455910 455930 455950 455970 455990
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40° 23' 6'' N
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40° 23' 6'' N
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'
W
40° 23' 2'' N
10
5
°
3
1
'
1
6
'
'
W
40° 23' 2'' N
10
5
°
3
1
'
6
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 15 30 60 90
Meters
Map Scale: 1:1,040 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Estes Park Area, Colorado, Parts of Boulder
and Larimer Counties
Survey Area Data: Version 10, Aug 29, 2024
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
Custom Soil Resource Report
10
MAP LEGEND MAP INFORMATION
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
11
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
32 Rock outcrop-Cathedral
complex, 20 to 100 percent
slopes
1.4 42.6%
50 Cathedral-Ratake complex, 5 to
15 percent slopes
1.9 57.4%
Totals for Area of Interest 3.3 100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas. A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils. On the
landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is made
up of the soils or miscellaneous areas for which it is named and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management. These are called contrasting, or dissimilar, components. They
generally are in small areas and could not be mapped separately because of the
scale used. Some small areas of strongly contrasting soils or miscellaneous areas
are identified by a special symbol on the maps. If included in the database for a
given area, the contrasting minor components are identified in the map unit
descriptions along with some characteristics of each. A few areas of minor
components may not have been observed, and consequently they are not
mentioned in the descriptions, especially where the pattern was so complex that it
was impractical to make enough observations to identify all the soils and
miscellaneous areas on the landscape.
The presence of minor components in a map unit in no way diminishes the
usefulness or accuracy of the data. The objective of mapping is not to delineate
pure taxonomic classes but rather to separate the landscape into landforms or
landform segments that have similar use and management requirements. The
delineation of such segments on the map provides sufficient information for the
Custom Soil Resource Report
12
development of resource plans. If intensive use of small areas is planned, however,
onsite investigation is needed to define and locate the soils and miscellaneous
areas.
An identifying symbol precedes the map unit name in the map unit descriptions.
Each description includes general facts about the unit and gives important soil
properties and qualities.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major
horizons that are similar in composition, thickness, and arrangement.
Soils of one series can differ in texture of the surface layer, slope, stoniness,
salinity, degree of erosion, and other characteristics that affect their use. On the
basis of such differences, a soil series is divided into soil phases. Most of the areas
shown on the detailed soil maps are phases of soil series. The name of a soil phase
commonly indicates a feature that affects use or management. For example, Alpha
silt loam, 0 to 2 percent slopes, is a phase of the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
A complex consists of two or more soils or miscellaneous areas in such an intricate
pattern or in such small areas that they cannot be shown separately on the maps.
The pattern and proportion of the soils or miscellaneous areas are somewhat similar
in all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of present
or anticipated uses of the map units in the survey area, it was not considered
practical or necessary to map the soils or miscellaneous areas separately. The
pattern and relative proportion of the soils or miscellaneous areas are somewhat
similar. Alpha-Beta association, 0 to 2 percent slopes, is an example.
An undifferentiated group is made up of two or more soils or miscellaneous areas
that could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and proportion
of the soils or miscellaneous areas in a mapped area are not uniform. An area can
be made up of only one of the major soils or miscellaneous areas, or it can be made
up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.
Some surveys include miscellaneous areas. Such areas have little or no soil
material and support little or no vegetation. Rock outcrop is an example.
Custom Soil Resource Report
13
Estes Park Area, Colorado, Parts of Boulder and Larimer Counties
32—Rock outcrop-Cathedral complex, 20 to 100 percent slopes
Map Unit Setting
National map unit symbol: jzyq
Elevation: 7,600 to 9,100 feet
Mean annual precipitation: 18 to 22 inches
Mean annual air temperature: 42 to 44 degrees F
Frost-free period: 75 to 100 days
Farmland classification: Not prime farmland
Map Unit Composition
Rock outcrop:45 percent
Cathedral and similar soils:40 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Rock Outcrop
Setting
Landform:Mountain slopes
Landform position (three-dimensional):Mountainflank, free face
Down-slope shape:Convex
Across-slope shape:Convex
Parent material:Granite and/or gneiss and/or schist
Typical profile
R - 0 to 60 inches: bedrock
Properties and qualities
Slope:20 to 100 percent
Depth to restrictive feature:0 inches to lithic bedrock
Runoff class: Very high
Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately
low (0.00 to 0.01 in/hr)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 8
Hydrologic Soil Group: D
Hydric soil rating: No
Description of Cathedral
Setting
Landform:Mountain slopes
Landform position (three-dimensional):Mountainflank
Down-slope shape:Linear
Across-slope shape:Convex, linear
Parent material:Gravelly slope alluvium and/or colluvium derived from granite,
gneiss, and/or schist
Typical profile
A - 0 to 9 inches: very gravelly sandy loam
Bw - 9 to 15 inches: extremely gravelly sandy loam
Custom Soil Resource Report
14
R - 15 to 25 inches: bedrock
Properties and qualities
Slope:20 to 80 percent
Depth to restrictive feature:10 to 20 inches to lithic bedrock
Drainage class:Somewhat excessively drained
Runoff class: Very high
Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately
low (0.00 to 0.06 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Available water supply, 0 to 60 inches: Very low (about 0.8 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 7e
Hydrologic Soil Group: D
Ecological site: F048AY439UT - Mountain Shallow Loam (Ponderosa pine)
Other vegetative classification: Ponderosa pine/antelope bitterbrush (PIPO/
PUTR2) (C1120)
Hydric soil rating: No
Minor Components
Chasmfalls
Percent of map unit:10 percent
Landform:Mountain slopes
Landform position (two-dimensional):Backslope, footslope
Landform position (three-dimensional):Mountainbase
Ecological site:R048AY255CO - Pine Grasslands
Other vegetative classification:Ponderosa pine/antelope bitterbrush (PIPO/
PUTR2) (C1120)
Hydric soil rating: No
Legault
Percent of map unit:5 percent
Landform:Mountain slopes
Landform position (two-dimensional):Shoulder, backslope
Landform position (three-dimensional):Mountainflank
Other vegetative classification:Lodgepole pine/kinnikinnick (PICO/ARUV) (C0901)
Hydric soil rating: No
50—Cathedral-Ratake complex, 5 to 15 percent slopes
Map Unit Setting
National map unit symbol: 2lsst
Elevation: 7,500 to 8,200 feet
Mean annual precipitation: 14 to 20 inches
Mean annual air temperature: 41 to 44 degrees F
Custom Soil Resource Report
15
Frost-free period: 95 to 105 days
Farmland classification: Not prime farmland
Map Unit Composition
Cathedral and similar soils:45 percent
Ratake and similar soils:40 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Cathedral
Setting
Landform:Hills
Landform position (two-dimensional):Backslope
Landform position (three-dimensional):Side slope
Down-slope shape:Convex
Across-slope shape:Convex, linear
Parent material:Slope alluvium derived from granite and gneiss
Typical profile
A - 0 to 3 inches: gravelly sandy loam
Bw1 - 3 to 10 inches: very gravelly coarse sandy loam
Bw2 - 10 to 18 inches: extremely gravelly coarse sandy loam
R - 18 to 28 inches: bedrock
Properties and qualities
Slope:5 to 15 percent
Depth to restrictive feature:9 to 20 inches to lithic bedrock
Drainage class:Well drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately
low (0.00 to 0.01 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Maximum salinity:Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water supply, 0 to 60 inches: Very low (about 1.4 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 6s
Hydrologic Soil Group: D
Ecological site: F048AY439UT - Mountain Shallow Loam (Ponderosa pine)
Other vegetative classification: Ponderosa pine/antelope bitterbrush (PIPO/
PUTR2) (C1120)
Hydric soil rating: No
Description of Ratake
Setting
Landform:Hills
Landform position (two-dimensional):Shoulder
Landform position (three-dimensional):Side slope
Down-slope shape:Convex
Across-slope shape:Convex, linear
Parent material:Slope alluvium derived from granite and gneiss over residuum
weathered from granite and gneiss
Custom Soil Resource Report
16
Typical profile
A - 0 to 7 inches: gravelly sandy loam
Bw - 7 to 15 inches: very gravelly sandy loam
Cr - 15 to 24 inches: bedrock
Properties and qualities
Slope:5 to 15 percent
Depth to restrictive feature:9 to 20 inches to paralithic bedrock
Drainage class:Well drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately
low (0.00 to 0.06 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Maximum salinity:Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water supply, 0 to 60 inches: Very low (about 1.4 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 6s
Hydrologic Soil Group: D
Ecological site: F048AY439UT - Mountain Shallow Loam (Ponderosa pine)
Other vegetative classification: Ponderosa pine/antelope bitterbrush (PIPO/
PUTR2) (C1120)
Hydric soil rating: No
Minor Components
Rock outcrop
Percent of map unit:10 percent
Landform:Rock pediments
Down-slope shape:Convex
Across-slope shape:Convex
Hydric soil rating: Unranked
Chasmfalls
Percent of map unit:5 percent
Landform:Pediments
Ecological site:R048AY222CO - Loamy Park
Hydric soil rating: No
Custom Soil Resource Report
17
References
American Association of State Highway and Transportation Officials (AASHTO).
2004. Standard specifications for transportation materials and methods of sampling
and testing. 24th edition.
American Society for Testing and Materials (ASTM). 2005. Standard classification of
soils for engineering purposes. ASTM Standard D2487-00.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of
wetlands and deep-water habitats of the United States. U.S. Fish and Wildlife
Service FWS/OBS-79/31.
Federal Register. July 13, 1994. Changes in hydric soils of the United States.
Federal Register. September 18, 2002. Hydric soils of the United States.
Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric
soils in the United States.
National Research Council. 1995. Wetlands: Characteristics and boundaries.
Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service.
U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/national/soils/?cid=nrcs142p2_054262
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for
making and interpreting soil surveys. 2nd edition. Natural Resources Conservation
Service, U.S. Department of Agriculture Handbook 436. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577
Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of
Agriculture, Natural Resources Conservation Service. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580
Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and
Delaware Department of Natural Resources and Environmental Control, Wetlands
Section.
United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of
Engineers wetlands delineation manual. Waterways Experiment Station Technical
Report Y-87-1.
United States Department of Agriculture, Natural Resources Conservation Service.
National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/
home/?cid=nrcs142p2_053374
United States Department of Agriculture, Natural Resources Conservation Service.
National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/
detail/national/landuse/rangepasture/?cid=stelprdb1043084
18
United States Department of Agriculture, Natural Resources Conservation Service.
National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/soils/scientists/?cid=nrcs142p2_054242
United States Department of Agriculture, Natural Resources Conservation Service.
2006. Land resource regions and major land resource areas of the United States,
the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook
296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?
cid=nrcs142p2_053624
United States Department of Agriculture, Soil Conservation Service. 1961. Land
capability classification. U.S. Department of Agriculture Handbook 210. http://
www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf
Custom Soil Resource Report
19
RAINFALL DATA
NOAA Atlas 14, Volume 8, Version 2
Location name: Estes Park, Colorado, USA*
Latitude: 40.3847°, Longitude: -105.5195°
Elevation: 7716 ft**
* source: ESRI Maps
** source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale
Unruh, Michael Yekta, Geoffery Bonnin
NOAA, National Weather Service, Silver Spring, Maryland
PF_tabular | PF_graphical | Maps_&_aerials
PF tabular
AMS-based point precipitation frequency estimates with 90% confidence intervals (in
inches)1
Duration Annual exceedance probability (1/years)
1/2 1/5 1/10 1/25 1/50 1/100 1/200 1/500 1/1000
5-min 0.212
(0.163‑0.276)
0.285
(0.218‑0.372)
0.362
(0.277‑0.476)
0.494
(0.378‑0.714)
0.617
(0.455‑0.895)
0.758
(0.540‑1.13)
0.918
(0.628‑1.41)
1.16
(0.762‑1.84)
1.36
(0.864‑2.16)
10-min 0.310
(0.239‑0.403)
0.417
(0.320‑0.545)
0.531
(0.405‑0.697)
0.724
(0.554‑1.05)
0.903
(0.667‑1.31)
1.11
(0.790‑1.65)
1.34
(0.920‑2.07)
1.70
(1.12‑2.69)
2.00
(1.26‑3.16)
15-min 0.378
(0.291‑0.492)
0.509
(0.390‑0.664)
0.647
(0.494‑0.850)
0.883
(0.676‑1.28)
1.10
(0.813‑1.60)
1.35
(0.964‑2.02)
1.64
(1.12‑2.52)
2.07
(1.36‑3.28)
2.44
(1.54‑3.85)
30-min 0.476
(0.367‑0.620)
0.639
(0.490‑0.835)
0.814
(0.621‑1.07)
1.11
(0.854‑1.61)
1.39
(1.03‑2.02)
1.72
(1.22‑2.56)
2.08
(1.43‑3.21)
2.64
(1.74‑4.18)
3.11
(1.97‑4.91)
60-min 0.596
(0.459‑0.775)
0.767
(0.589‑1.00)
0.969
(0.740‑1.27)
1.33
(1.03‑1.95)
1.68
(1.25‑2.45)
2.09
(1.49‑3.13)
2.56
(1.76‑3.95)
3.28
(2.16‑5.20)
3.90
(2.47‑6.15)
2-hr 0.715
(0.557‑0.920)
0.895
(0.695‑1.16)
1.12
(0.868‑1.46)
1.55
(1.22‑2.25)
1.97
(1.48‑2.85)
2.46
(1.78‑3.66)
3.04
(2.11‑4.65)
3.92
(2.61‑6.17)
4.68
(2.99‑7.32)
3-hr 0.811
(0.636‑1.04)
0.986
(0.771‑1.27)
1.23
(0.954‑1.58)
1.69
(1.34‑2.45)
2.15
(1.63‑3.11)
2.70
(1.97‑4.00)
3.34
(2.34‑5.10)
4.34
(2.92‑6.80)
5.20
(3.35‑8.09)
6-hr 1.00
(0.796‑1.27)
1.20
(0.948‑1.52)
1.47
(1.16‑1.88)
2.00
(1.60‑2.86)
2.52
(1.94‑3.60)
3.15
(2.32‑4.61)
3.88
(2.75‑5.86)
5.02
(3.41‑7.79)
6.01
(3.91‑9.24)
12-hr 1.23
(0.987‑1.53)
1.50
(1.20‑1.88)
1.83
(1.46‑2.31)
2.42
(1.94‑3.38)
2.99
(2.31‑4.19)
3.67
(2.73‑5.27)
4.45
(3.17‑6.60)
5.64
(3.86‑8.61)
6.66
(4.38‑10.1)
24-hr 1.48
(1.21‑1.83)
1.87
(1.52‑2.32)
2.28
(1.84‑2.84)
2.96
(2.37‑4.02)
3.58
(2.78‑4.90)
4.29
(3.21‑6.05)
5.10
(3.66‑7.44)
6.32
(4.35‑9.50)
7.34
(4.88‑11.1)
2-day 1.75
(1.44‑2.14)
2.28
(1.87‑2.80)
2.78
(2.27‑3.43)
3.58
(2.89‑4.76)
4.28
(3.35‑5.76)
5.07
(3.83‑7.03)
5.95
(4.31‑8.54)
7.25
(5.04‑10.7)
8.33
(5.59‑12.4)
3-day 1.91
(1.58‑2.31)
2.52
(2.08‑3.07)
3.08
(2.54‑3.78)
3.97
(3.22‑5.23)
4.74
(3.73‑6.32)
5.60
(4.25‑7.70)
6.55
(4.77‑9.33)
7.94
(5.55‑11.7)
9.10
(6.14‑13.5)
4-day 2.03
(1.70‑2.45)
2.70
(2.24‑3.27)
3.30
(2.73‑4.02)
4.24
(3.45‑5.55)
5.05
(3.99‑6.70)
5.96
(4.54‑8.14)
6.95
(5.08‑9.84)
8.40
(5.90‑12.3)
9.60
(6.51‑14.1)
7-day 2.39
(2.01‑2.85)
3.11
(2.62‑3.73)
3.76
(3.14‑4.54)
4.74
(3.88‑6.11)
5.58
(4.45‑7.30)
6.51
(5.00‑8.79)
7.52
(5.54‑10.5)
8.98
(6.36‑13.0)
10.2
(6.98‑14.9)
10-day 2.71
(2.30‑3.22)
3.46
(2.93‑4.13)
4.12
(3.47‑4.94)
5.11
(4.20‑6.52)
5.95
(4.76‑7.71)
6.86
(5.30‑9.18)
7.85
(5.81‑10.9)
9.27
(6.59‑13.3)
10.4
(7.18‑15.2)
20-day 3.62
(3.12‑4.25)
4.48
(3.84‑5.27)
5.19
(4.42‑6.15)
6.20
(5.14‑7.73)
7.03
(5.68‑8.93)
7.91
(6.16‑10.4)
8.84
(6.60‑12.1)
10.1
(7.28‑14.3)
11.2
(7.79‑16.1)
30-day 4.37
(3.79‑5.09)
5.37
(4.64‑6.28)
6.16
(5.30‑7.25)
7.26
(6.04‑8.93)
8.12
(6.60‑10.2)
9.02
(7.07‑11.7)
9.95
(7.47‑13.4)
11.2
(8.09‑15.7)
12.2
(8.56‑17.4)
45-day 5.32
(4.65‑6.16)
6.56
(5.72‑7.62)
7.51
(6.51‑8.78)
8.78
(7.33‑10.7)
9.74
(7.95‑12.1)
10.7
(8.44‑13.8)
11.7
(8.82‑15.6)
13.0
(9.42‑18.0)
14.0
(9.87‑19.9)
60-day 6.13
(5.39‑7.06)
7.62
(6.68‑8.81)
8.74
(7.61‑10.2)
10.2
(8.54‑12.3)
11.3
(9.25‑13.9)
12.4
(9.77‑15.8)
13.4
(10.2‑17.8)
14.8
(10.8‑20.4)
15.9
(11.2‑22.4)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of annual maxima series (AMS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation
frequency estimates (for a given duration and annual exceedance probability) will be greater than the upper bound (or less than the lower
bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than
currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
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National Oceanic and Atmospheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questions@noaa.gov
Disclaimer
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100km
60mi
PRELIMINARY DRAINAGE
CALCULATIONS
This method is in accoradance with the 2014 VHE drainage report for comparison purpose
Basin Land Total
Identifier Coverage "c" Area Area Weighted Notes
Type value (acres) (acres) "c"
Rock outcropping 0.90 0.06
Natural/meadow 0.30 0.04
0.10 0.66 Same "c" value as 2014 report
Rock outcropping 0.90 0.05
Building 0.90 0.11
Paved Road 0.90 0.01
Natural/meadow 0.30 0.19
0.35 0.58 "c" value from 2014 report = 0.55
Rock outcropping 0.90 0.35
Building 0.90 0.42
Paved Road 0.90 0.48
Natural/meadow 0.30 1.51
2.76 0.57 "c" value from 2014 report = 0.52
Building 0.90 0.11
Paved Road 0.90 0.07
Natural/meadow 0.30 0.48
0.67 0.47 "c" value from 2014 report = 0.45 for overall C-3 basin = 10.73 acre
Storm "c"
Basin Recurrence Value Weighted Adjusted
Identifier Interval Multiplier "c" "c" Value
2 yr 1 0.66 0.66
10 yr 1 0.66 0.66
100 yr 1.25 0.66 0.83
2 yr 1 0.58 0.58
10 yr 1 0.58 0.58
100 yr 1.25 0.58 0.72
2 yr 1 0.57 0.57
10 yr 1 0.57 0.57
100 yr 1.25 0.57 0.72
2 yr 1 0.47 0.47
10 yr 1 0.47 0.47
100 yr 1.25 0.47 0.58
C-3
B-2
C-3
(project
area)
Portion of C-3 drainage basin within Freelan Heights project area, new improvements account
for 28% impervious coverage < 40% assumption in SWC Phase 1 drainage report for
downstream detention on Amended Lot 4 SHD
B-2
Updated weighted "c" value for each developed drainage basin
A
B-1
No development coverage this basinA
B-1
Project Title:
Channel ID:UNDEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 2 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.320 2.560 0.670
Runoff Coefficient, C = 0.66 0.41 0.41 0.34
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 423 200
Flow Velocity (fps) = 1.08 0.41 0.59 0.38
Flow Time (min.) = 4.21 6.15 12.03 8.73
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =4.21 6.24 12.68 23.58
User-Entered Tc (min)= 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =2.83 2.70 2.00 1.90
Computed Tc Peak Flowrate, (cfs) Qp = 0.19 0.35 2.10 0.43
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Project Title:
Channel ID:UNDEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 10 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.320 2.560 0.670
Runoff Coefficient, C = 0.66 0.41 0.41 0.34
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 431 200
Flow Velocity (fps) = 1.08 0.41 0.59 0.38
Flow Time (min.) = 4.21 6.15 12.14 8.73
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =4.21 6.24 12.79 23.58
User-Entered Tc (min)= 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =4.83 4.60 3.50 3.30
Computed Tc Peak Flowrate, (cfs) Qp = 0.32 0.60 3.67 0.75
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Project Title:
Channel ID:UNDEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 100 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.320 2.560 0.670
Runoff Coefficient, C = 0.83 0.51 0.51 0.43
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 431 200
Flow Velocity (fps) = 1.77 0.48 0.69 0.43
Flow Time (min.) = 2.59 5.26 10.38 7.70
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =2.59 5.35 11.03 22.54
User-Entered Tc (min)= 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =7.67 7.60 5.80 5.50
Computed Tc Peak Flowrate, (cfs) Qp = 0.64 1.24 7.57 1.58
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Project Title:
Channel ID:DEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 2 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.350 2.760 0.670
Runoff Coefficient, C = 0.66 0.58 0.57 0.47
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 431 200
Flow Velocity (fps) = 1.08 0.55 0.77 0.46
Flow Time (min.) = 4.21 4.63 9.33 7.24
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =4.21 4.73 9.98 22.08
User-Entered Tc (min)= 5.00 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =2.83 2.83 2.20 1.90
Computed Tc Peak Flowrate, (cfs) Qp = 0.19 0.57 3.46 0.60
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Project Title:
Channel ID:DEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 10 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.350 2.760 0.670
Runoff Coefficient, C = 0.66 0.58 0.57 0.47
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 431 200
Flow Velocity (fps) = 1.08 0.55 0.77 0.46
Flow Time (min.) = 4.21 4.63 9.33 7.24
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =4.21 4.73 9.98 22.08
User-Entered Tc (min)= 5.00 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =4.83 4.83 3.70 3.30
Computed Tc Peak Flowrate, (cfs) Qp = 0.32 0.98 5.82 1.04
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Project Title:
Channel ID:DEVELOPED DRAINAGE BASIN DISCHARGE
Design Storm Return Period, Tr = 100 years
Catchment Hydrologic Data
Catchment ID =B-1 B-2 C-3
rea (Acres) = 0.100 0.350 2.760 0.670
Runoff Coefficient, C = 0.83 0.72 0.72 0.58
Time of Concentration
Overland Flow Slope (%) = 83.0000 41.0000
(overland flow length <500 ft)Length (ft) =84 215
Flow Velocity (fps) =15.00 5.50
Flow Time (min.) =0.09 0.65
Reach 1 Slope (%) = 35 18 11 12.5
Length (ft) = 274 153 431 200
Flow Velocity (fps) = 1.77 0.75 1.07 0.56
Flow Time (min.) = 2.59 3.39 6.69 5.98
Reach 2 Slope (%) =4
Length (ft) =130
Flow Velocity (fps) =0.15
Flow Time (min.) =14.84
Times Compu e c m n =2.59 3.48 7.34 20.82
User-Entered Tc (min)= 5.00 5.00
Peak Runoff Prediction (from IDF Curve for Estes Park)
Rainfall Intensity at Computed Tc, (in/hr) I =7.67 7.67 6.40 5.50
Computed Tc Peak Flowrate, (cfs) Qp = 0.64 1.93 12.72 2.14
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Freelan Heights
Designer:
Company:2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
Date:1-hour rainfall depth, P1 (in) =0.60 0.77 0.97 1.33 1.68 2.09 3.28
Project:a b c
Location:Rainfall Intensity Equation Coefficients =28.50 10.00 0.786
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
Overland
Flow Length
Li (ft)
U/S Elevation
(ft)
(Optional)
D/S Elevation
(ft)
(Optional)
Overland
Flow Slope
Si (ft/ft)
Overland
Flow Time
ti (min)
Channelized
Flow Length
Lt (ft)
U/S Elevation
(ft)
(Optional)
D/S Elevation
(ft)
(Optional)
Channelized
Flow Slope
St (ft/ft)
NRCS
Conveyance
Factor K
Channelized
Flow Velocity
Vt (ft/sec)
Channelized
Flow Time
tt (min)
Computed
tc (min)
Regional
tc (min)
Selected
tc (min)2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
0.39 0.45 0.51 0.60 0.64 0.69 0.75 6.00 6.00 6.00 1.92 2.48 3.13 4.29 5.42 6.74 10.57 0.08 0.11 0.16 0.26 0.35 0.47 0.80
0.50 0.55 0.60 0.67 0.70 0.74 0.79 4.50 4.50 5.00 2.02 2.61 3.29 4.51 5.70 7.09 11.13 0.35 0.50 0.69 1.06 1.40 1.84 3.06
0.37 0.43 0.48 0.59 0.63 0.68 0.74 5.24 7.40 7.40 1.80 2.32 2.93 4.01 5.07 6.31 9.90 1.82 2.73 3.92 6.51 8.82 11.84 20.20
0.20 0.26 0.34 0.48 0.53 0.60 0.68 9.28 9.83 9.83 1.63 2.10 2.64 3.62 4.58 5.69 8.93 0.22 0.37 0.60 1.15 1.63 2.28 4.05
0.01 0.05 0.15 0.33 0.40 0.49 0.59 11.64 11.64 11.64 1.52 1.96 2.47 3.38 4.27 5.32 8.34 0.01 0.07 0.24 0.75 1.15 1.75 3.32
63.0
0.350274.00
Rainfall Intensity, I (in/hr)
1.00 0.00 17.33100.0100.00
Peak Flow, Q (cfs)
Calculation of Peak Runoff using Rational Method
Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of ConcentrationRunoff Coefficient, C
Subcatchment Name Area
(ac)
NRCS
Hydrologic
Soil Group
Percent
Imperviousness
Basin A (No developed area) 0.10 D 51.0
Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link)
Cells of this color are for required user-input
Cells of this color are for optional override values
Cells of this color are for calculated results based on overrides
FER
Van Horn Engineering
9/26/2025
Freelan Heights
Overlook Court
Version 2.00 released May 2017
20 4.00 0.54
15.29
2.76 D 48.0 215.00 0.410 431.00 0.110 10 3.32 2.17
0.010 10 1.00 0.00D237.00 0.410 0.00
25.66
22.08
200.00 0.125 0.00 0.010 10 1.00 0.00
19.22
200.00 0.125 130.00 0.040
D
Basin B2 (Developed)
28.0D0.67Basin C3 (Developed - project site only)
2.0D0.67Basin C3 (Uneveloped - project site only)
0.35Basin B1 (Develped)
D
I 𝑖𝑛/ℎ𝑟 a ∗P
b t
t 0.395 1.1 C L
S .
t L
60K S L
60V
Computed t t t
Regional t 26 17i L
60 14i 9 S Selected t max t ,min Computed t ,Regional t
t 5 (urban)
t 10 (non-urban)
Q 𝑐𝑓𝑠 CIA
Project:
Basin ID:
Design Information (Input):Design Information (Input):
Catchment Drainage Imperviousness Ia = 48.00 percent Catchment Drainage Imperviousness Ia = 48.00 percent
Catchment Drainage Area A = 2.760 acres Catchment Drainage Area A = 2.760 acres
Predevelopment NRCS Soil Group Type = D A, B, C, or D Predevelopment NRCS Soil Group Type = D A, B, C, or D
Return Period for Detention Control T = 10 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100)
Time of Concentration of Watershed Tc = 7 minutes Time of Concentration of Watershed Tc = 7 minutes
Allowable Unit Release Rate q = 1.19 cfs/acre Allowable Unit Release Rate q = 2.49 cfs/acre
One-hour Precipitation P1 = 0.97 inches One-hour Precipitation P1 = 2.09 inches
Design Rainfall IDF Formula i = C1* P1/(C2+Tc)^C3 Design Rainfall IDF Formula i = C1* P1/(C2+Tc)^C3
Coefficient One C1 = 28.50 Coefficient One C1 = 28.50
Coefficient Two C2 = 10 Coefficient Two C2 = 10
Coefficient Three C3 = 0.789 Coefficient Three C3 = 0.789
Determination of Average Outflow from the Basin (Calculated):Determination of Average Outflow from the Basin (Calculated):
Runoff Coefficient C = 0.72 Runoff Coefficient C = 0.72
Inflow Peak Runoff Qp-in = 5.90 cfs Inflow Peak Runoff Qp-in = 12.72 cfs
Allowable Peak Outflow Rate Qp-out =3.29 cfs Allowable Peak Outflow Rate Qp-out =6.88 cfs
Mod. FAA Minor Storage Volume = 1,849 cubic feet Mod. FAA Major Storage Volume = 4,157 cubic feet
Mod. FAA Minor Storage Volume = 0.042 acre-ft Mod. FAA Major Storage Volume = 0.095 acre-ft
5 <- Enter Rainfall Duration Incremental Increase Value Here (e.g. 5 for 5-Minutes)
Rainfall Rainfall Inflow Adjustment Average Outflow Storage Rainfall Rainfall Inflow Adjustment Average Outflow Storage
Duration Intensity Volume Factor Outflow Volume Volume Duration Intensity Volume Factor Outflow Volume Volume
minutes inches / hr acre-feet "m"cfs acre-feet acre-feet minutes inches / hr acre-feet "m"cfs acre-feet acre-feet
(input)(output) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output) (output)
0 0.00 0.000 0.00 0.00 0.000 0.000 0 0.00 0.000 0.00 0.00 0.000 0.000
5 3.26 0.045 1.00 3.29 0.023 0.022 5 7.03 0.096 1.00 6.88 0.047 0.049
10 2.60 0.071 0.85 2.78 0.038 0.033 10 5.60 0.153 0.85 5.81 0.080 0.073
15 2.18 0.090 0.73 2.40 0.050 0.040 15 4.70 0.193 0.73 5.02 0.104 0.089
20 1.89 0.103 0.67 2.21 0.061 0.042 20 4.07 0.223 0.67 4.63 0.127 0.095
25 1.67 0.114 0.64 2.10 0.072 0.042 25 3.60 0.247 0.64 4.39 0.151 0.095
30 1.51 0.124 0.62 2.02 0.084 0.040 30 3.24 0.266 0.62 4.23 0.175 0.091
35 1.37 0.131 0.60 1.97 0.095 0.036 35 2.96 0.283 0.60 4.12 0.199 0.085
40 1.26 0.138 0.59 1.93 0.106 0.032 40 2.72 0.298 0.59 4.03 0.222 0.076
45 1.17 0.144 0.58 1.90 0.118 0.027 45 2.52 0.311 0.58 3.97 0.246 0.065
50 1.09 0.150 0.57 1.87 0.129 0.021 50 2.36 0.322 0.57 3.91 0.270 0.053
55 1.03 0.154 0.56 1.85 0.140 0.014 55 2.21 0.333 0.56 3.87 0.293 0.040
60 0.97 0.159 0.56 1.83 0.152 0.007 60 2.09 0.343 0.56 3.84 0.317 0.026
65 0.92 0.163 0.55 1.82 0.163 0.000 65 1.98 0.351 0.55 3.81 0.341 0.011
70 0.87 0.167 0.55 1.81 0.174 -0.007 70 1.88 0.360 0.55 3.78 0.364 -0.005
75 0.83 0.170 0.55 1.80 0.186 -0.015 75 1.79 0.367 0.55 3.76 0.388 -0.021
80 0.79 0.174 0.54 1.79 0.197 -0.023 80 1.71 0.375 0.54 3.74 0.412 -0.037
85 0.76 0.177 0.54 1.78 0.208 -0.031 85 1.64 0.381 0.54 3.72 0.435 -0.054
90 0.73 0.180 0.54 1.77 0.220 -0.040 90 1.57 0.388 0.54 3.70 0.459 -0.071
95 0.70 0.183 0.54 1.76 0.231 -0.048 95 1.51 0.394 0.54 3.69 0.483 -0.089
100 0.68 0.185 0.53 1.76 0.242 -0.057 100 1.46 0.400 0.53 3.68 0.507 -0.107
105 0.65 0.188 0.53 1.75 0.254 -0.066 105 1.41 0.405 0.53 3.67 0.530 -0.125
110 0.63 0.190 0.53 1.75 0.265 -0.074 110 1.36 0.410 0.53 3.66 0.554 -0.143
115 0.61 0.193 0.53 1.74 0.276 -0.083 115 1.32 0.415 0.53 3.65 0.578 -0.162
120 0.59 0.195 0.53 1.74 0.288 -0.092 120 1.28 0.420 0.53 3.64 0.601 -0.181
125 0.58 0.197 0.53 1.74 0.299 -0.102 125 1.24 0.425 0.53 3.63 0.625 -0.200
130 0.56 0.199 0.53 1.73 0.310 -0.111 130 1.21 0.429 0.53 3.62 0.649 -0.219
135 0.54 0.201 0.53 1.73 0.322 -0.120 135 1.17 0.434 0.53 3.62 0.672 -0.239
140 0.53 0.203 0.52 1.73 0.333 -0.130 140 1.14 0.438 0.52 3.61 0.696 -0.258
145 0.52 0.205 0.52 1.72 0.344 -0.139 145 1.11 0.442 0.52 3.60 0.720 -0.278
150 0.50 0.207 0.52 1.72 0.356 -0.149 150 1.09 0.446 0.52 3.60 0.743 -0.297
155 0.49 0.209 0.52 1.72 0.367 -0.158 155 1.06 0.450 0.52 3.59 0.767 -0.317
160 0.48 0.210 0.52 1.72 0.378 -0.168 160 1.04 0.454 0.52 3.59 0.791 -0.337
165 0.47 0.212 0.52 1.71 0.389 -0.177 165 1.01 0.457 0.52 3.58 0.815 -0.357
170 0.46 0.214 0.52 1.71 0.401 -0.187 170 0.99 0.461 0.52 3.58 0.838 -0.378
175 0.45 0.215 0.52 1.71 0.412 -0.197 175 0.97 0.464 0.52 3.58 0.862 -0.398
180 0.44 0.217 0.52 1.71 0.423 -0.207 180 0.95 0.467 0.52 3.57 0.886 -0.418
185 0.43 0.218 0.52 1.71 0.435 -0.216 185 0.93 0.471 0.52 3.57 0.909 -0.439
190 0.42 0.220 0.52 1.70 0.446 -0.226 190 0.91 0.474 0.52 3.56 0.933 -0.459
195 0.41 0.221 0.52 1.70 0.457 -0.236 195 0.89 0.477 0.52 3.56 0.957 -0.480
200 0.41 0.223 0.52 1.70 0.469 -0.246 200 0.88 0.480 0.52 3.56 0.980 -0.501
205 0.40 0.224 0.52 1.70 0.480 -0.256 205 0.86 0.483 0.52 3.56 1.004 -0.521
210 0.39 0.225 0.52 1.70 0.491 -0.266 210 0.84 0.486 0.52 3.55 1.028 -0.542
215 0.39 0.227 0.52 1.70 0.503 -0.276 215 0.83 0.488 0.52 3.55 1.051 -0.563
220 0.38 0.228 0.52 1.70 0.514 -0.286 220 0.82 0.491 0.52 3.55 1.075 -0.584
225 0.37 0.229 0.52 1.70 0.525 -0.296 225 0.80 0.494 0.52 3.55 1.099 -0.605
230 0.37 0.230 0.52 1.69 0.537 -0.306 230 0.79 0.497 0.52 3.54 1.123 -0.626
235 0.36 0.232 0.51 1.69 0.548 -0.316 235 0.78 0.499 0.51 3.54 1.146 -0.647
240 0.35 0.233 0.51 1.69 0.559 -0.327 240 0.76 0.502 0.51 3.54 1.170 -0.668
245 0.35 0.234 0.51 1.69 0.571 -0.337 245 0.75 0.504 0.51 3.54 1.194 -0.689
250 0.34 0.235 0.51 1.69 0.582 -0.347 250 0.74 0.507 0.51 3.53 1.217 -0.710
255 0.34 0.236 0.51 1.69 0.593 -0.357 255 0.73 0.509 0.51 3.53 1.241 -0.732
260 0.33 0.237 0.51 1.69 0.605 -0.367 260 0.72 0.512 0.51 3.53 1.265 -0.753
265 0.33 0.239 0.51 1.69 0.616 -0.378 265 0.71 0.514 0.51 3.53 1.288 -0.774
270 0.32 0.240 0.51 1.69 0.627 -0.388 270 0.70 0.516 0.51 3.53 1.312 -0.796
275 0.32 0.241 0.51 1.69 0.639 -0.398 275 0.69 0.519 0.51 3.53 1.336 -0.817
280 0.32 0.242 0.51 1.69 0.650 -0.408 280 0.68 0.521 0.51 3.52 1.359 -0.839
285 0.31 0.243 0.51 1.68 0.661 -0.419 285 0.67 0.523 0.51 3.52 1.383 -0.860
290 0.31 0.244 0.51 1.68 0.673 -0.429 290 0.66 0.525 0.51 3.52 1.407 -0.882
295 0.30 0.245 0.51 1.68 0.684 -0.439 295 0.65 0.527 0.51 3.52 1.430 -0.903
300 0.30 0.246 0.51 1.68 0.695 -0.450 300 0.64 0.529 0.51 3.52 1.454 -0.925
Mod. FAA Minor Storage Volume (cubic ft.) = 1,849 Mod. FAA Major Storage Volume (cubic ft.) = 4,157
Mod. FAA Minor Storage Volume (acre-ft.) = 0.0424 Mod. FAA Major Storage Volume (acre-ft.) = 0.0954
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Freelan Heights
Proposed Conditions Detention Pond Size Verification
Determination of MAJOR Detention Volume Using Modified FAA Method
(For catchments less than 160 acres only. For larger catchments, use hydrograph routing method)
(NOTE: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended)
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.34, Released November 2013
Determination of MINOR Detention Volume Using Modified FAA Method
Full Site Detention 7-3-2025.xls, Modified FAA 9/26/2025, 4:20 PM
Project:
Basin ID:
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Freelan Heights
Proposed Conditions Detention Pond Size Verification
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.34, Released November 2013
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Duration (Minutes)
Inflow and Outflow Volumes vs. Rainfall Duration
Minor Storm Inflow Volume Minor Storm Outflow Volume Minor Storm Storage Volume Major Storm Inflow Volume Major Storm Outflow Volume Major Storm Storage Volume
Full Site Detention 7-3-2025.xls, Modified FAA 9/26/2025, 4:20 PM
PREVIOUS DRAINAGE REPORTS
Photo #1 Uphill Overlook Basin Photo #2 Old utility tank near north boundary (on left)
Photo #3 Further east uphill Overlook Photo #4 Within Overlook (West Side)
Photo #5 Outfall west pond Photo #6 Northeast corner Overlook
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Photo #7 Northeast corner Overlook Photo #8 Lack of swale center- east Overlook
Photo #9 East inlet north of parking lot Photo #10 West inlet north of parking lot
Photo #11 Inside of round inlet Photo #12 Inside of round inlet
Photo #13 Inside of round inlet Photo #14 Inside of southeast parking lot Type R catch basin
Photo #15 Round inlet before clearing Photo #16 Round inlet after some clearing
Photo #17 Inside of round inlet with grate off Photo #18 Example of downspouts buried
Photo #19 Downspouts buried Photo #20 Inside of southeast parking lot catch basin outlet pipe
Photo #21 Curb cut Overlook Lane Photo #22 Swale in downstream flow path
Photo #23 Down stream swale Photo #24 Swale conveyance to lower “12,200 CF” pond
Photo #25 Inlet to lower “12,200 CF” Pond Photo #26 Outlet of “12,200 CF” Pond
Photo #27 Outlet of “12,200 CF” Pond Photo #28 Inlet of “12,200 CF” Pond