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APPENDIX E
EXCERPT FROM PREVIOUS REPORTS
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
k
Design Procedure Form: Porous Landscape Detention (PLD)
Designer.
Company:
Date: 22, 1999
-September
Project:
Location:
3}�
1. Basin Storage Volume
( I, = 100% If all paved and roofed areas uls of PLD)
1, =
100.00 %
A) Tributary Area's Imperviousness Ratio (i = I,/ 100)
1 =
1.00
B) Contributing Watershed Area Including the PLD (Area)
Area =
10,000 square feet
-
c
C) Water Quality Capture Volume (WQCV)
WQCV =
0.40 . watershed inches
se
(WQCV=0.8"(0.91'1'-1.19-I'+0.78.1))
_
_
D) Design Volume: Voles = (WQCV / 12) " Area
Vol =
333.3 . cubic feet
2. PLD Surface Area (A�) and Average Depth (dam.)
Apw =
350 square feet
(d,,,: _ (Vol / Ate), Min=0.5, Max=-Iff)
d, _
0.95;.. ..feet
�
3. Base Course (See Figure PLD-1)
X
6" (Min.) Sandy Loam Turf Layer, Plus 18" (Min.)
1
Layer of 25% Peat and 75% Sand Mix, Plus 9"
t
(Min.) Layer of ASSHTO #8 Coarse Aggregate
(CDOT Section 703 Specification).
Other.
5. Draining of porous pavement (Check a, or b, or c, answer d)
X
Infiltration to Subgrade with Permeable
Based on answers to 5a through 5d, check the appropriate method
Membrane: 5(c) checked and 5(d) = no
a) Check box B subgrade is heavy or expansive day
Underdrain with Impermeable
".
b) Check box if subgrade is silty or clayey sands
PEXI
Membrane: 5(a) checked or 5(d) = yes
c) Check box if subgrade is well -draining soils
..
Underdrain with Permeable Membrane:
d) Does tributary catchment contain land uses that may have
5(b) checked and 5(d) = no
t
petroleum products, greases, or other chemicals
present, such as gas station, es no
-Other:
hardware store, restaurant, etc.? � X
i
}
Notes:
.... see' S:� _.zlc.��_
- •y. > "�';~=lmat
S-34 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
0.50
0.45
0.40
a 0.35
m
t
0.30
v
m
L
0.25
A
3
0.20
U
0.15
MIND]
t1111191
wncv=a•m or3_1 1%2+n Tan
6-hr drain time a = 0.7
12-hr drain time a = 0.8 -
24-hr drain time a = 0.9
40-hr drain time a = 1.0
d Detention Basin
Drain Time
Basin
Detention and Porous
Landscape Detention
12-hour Drain Time
0.00
V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Total Imperviousness Ratio (i =1 wg1100)
FIGURE PLD-2
Water Quality Capture.Volume (WQCV), 8e Percentile Runoff Event
9-1-99
Urban Drainage and Flood Control District
S-33
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
SLOTTED CURS
IN FLOW
IMPERMEABLE LINER
IF ON EXPANSIVE SOILS,
OTHERWISE USE
GEOTEXTILE LINER
OPTIONAL 100 YEAR
DETENTION
S WATER
aSURFACE l
v 1 /
75%ASTM C-33 SAND
25%PEAT MIX ,_...
3 TO < INCH DIA PERFORATED PIPE
UNDERDRAIN CONNECTED TO INLET
(MAY BE ELIMINATED IF UNDERLAYING
SOILS ARE SANDY)
OWIGATED TURF GRASS,
DRYLAND GRASSES, AND
OTHER PLANTINGS
r SANDY LOAM
TURFLAYER
INLET
S'MIN- T2-MAX /
AVERAGE DEPTH /
UB
OPnONAL 100-YEAR
DETENTION CONTROL
FIGURE PLD-1
Porous Landscape Detention
S-32 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
5. Average Depth Maintain the average WQCV depth between 6" and 12". Average depth
is defined as water volume divided by the water surface area.
6. Sand -Peat Mix Provide a minimum of a 12-inch thick layer above the base course
Filter Layer consisting of a thoroughly mixed ASTMC-3 Sand and Peat for filtration
and adsorption of constituents.
7. Irrigated Vegetative Provide a sandy loam turf layer above the sand -peat mix layer. This
Layer layer shall be no less than 6-inches thick, but a thicker layer is
recommended to promote healthier vegetation.
5.6 Design Example
Design forms that provide a means of documenting the design procedure are included in the Design
Forms section. A completed form follows as a design example.
9-1-99 S-31
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
site regardless of in -situ soil type. If sandy soils are present, the facility can be installed without an
underdrain (infiltration option); sandy subsoils is not a requirement. This BMP has a relatively flat surface
area, and may be more difficult to incorporate it into steeply sloping terrain.
5.3.3 Pollutant Removal. Although not tested to date in the Denver area, the amount of pollutant
removed by this BMP should be significant and should equal or exceed the removal rates provided by
sand filters. In addition to settling, PLD provides for filtering, adsorption, and biological uptake of
constituents in stormwater. See Table SQ-6 for estimated ranges in pollutant removals.
5.4 Design Considerations
Figure PLD-1 shows a cross-section for a PLD. When implemented using multiple small installations on
a site, it is increasingly important to accurately account for each upstream drainage area tributary to each
PLD site to make sure that each facility is properly sized, and that all portions of the development site
are directed to a PLD.
5.5 Design Procedure
The following steps outline the PLD design procedure and criteria.
1. Basin Storage Volume Provide a storage volume based on a 12-hour drain time.
A. Find the required storage volume (watershed inches of runoff):
Using the tributary areas imperviousness, determine the Required
WQCV (watershed inches of runoff) using Figure PLD-2, based on
the PLD 12-hour drain time.
B. Calculate the Design Volume in cubic feet as follows:
Design Volume = C WQCV) * Area
l 12
In which:
Area = The watershed area tributary to the extended
detention pond (square feet)
2. Surface Area Calculate the minimum required surface area as follows:
Surface Area = Design Volume in ft3
do,
in which,
d V = average depth of the PLD basin.
3. Base Coarses Provide base coarses as shown in Figure PLD-1.
4. Subbase If expansive soils are a concern, install an impermeable membrane and
place the base coarse on top of the membrane. If soils are not
expansive, use geotextile fabric to line the entire basin bottom and walls.
S-30 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
Installation of plant materials
Completed PLD facility during storm
event
5.3 Advantages/Disadvantages
5.3.1 General. A primary advantage of PLD is making it possible to provide WQCV on a site while
reducing the impact on developable land. It works well with irrigated bluegrass, whereas experience has
shown that conditions in the bottom of extended detention basins (EDBs) become too wet for bluegrass.
A PLD provides a natural moisture source for vegetation, enabling 'green areas"to exist with reduced
irrigation. The adjacent photograph shows an example of a relatively large PLD facility featuring a
bluegrass bottom with a putting green.
IL 19R
The primary disadvantage of PLD is a potential for
clogging if a moderate to high level of silts and clays is
allowed to flow into the facility. Also, this BMP needs to
be avoided close to building foundations or other areas
where expansive soils are present, although an
underdrain and impermeable liner can ameliorate some
of this concern.
5.3.2 Physical Site Suitability. If an underdrain system
is incorporated into this BMP, PLD is suited for about any
9-1-99
Urban Drainage and Flood Control District
WO-1
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MAN.M (V, $)
Parking lot island before installation of
PLD
Excavation and installation of underdrain.
Sandy material used as planting medium
Photos: Courtesy Prince Georges County
S-28 9-9-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
5.0 POROUS LANDSCAPE DETENTION (PLD) — SEDIMENTATION FACILITY
5.1 Description
Porous landscape detention (PLD) consists of a low lying vegetated area underlain by a sand bed with an
underdrain pipe. A shallow surcharge zone exists above the PLD for temporary storage of the WQCV.
During a storm, accumulated runoff ponds in the vegetated zone and gradually infiltrates into the
underlying sand bed, filling the void spaces of the sand. The underdrain gradually dewaters the sand bed
and discharges the runoff to a nearby channel, swale, or storm sewer. Like PPD, this BMP allows WQCV
to be provided on a site that has little open area available for stormwater detention.
5.2 General Application
5.2.1 Locating. A PLD can be located in just about any of the open areas of a site. It is ideally suited for
small installations such as:
• Parking lot islands
• Street medians
• Roadside swale features
• Site entrance or buffer features
This BMP may also be implemented at a larger scale, serving as an infiltration basin for an entire site if
desired provided the water quality capture volume and average depth requirements contained in this
section are met.
Vegetation may consist of irrigated bluegrass or natural grasses with shrub and tree plantings if desired.
5.2.2 Example Application. The following photos illustrate an installation of PLD in Prince Georges
County, Maryland.
9-1-99 S-27
Urban Drainage and Flood Control District
RUNOFF
DRAINAGE CRITERIA MANUAL (V. 1)
CA = Runoff coefficient for Natural Resources Conservation Service (NRCS) Type A soils }
CB = Runoff coefficient for NRCS Type B soils
Coo = Runoff coefficient for NRCS Type C and D soils
KA = Correction factor for Type A soils defined in Table RO-4
KcD = Correction factor for Type C and D soils defined in Table RO-4
TABLE RO-4
Correction Factors KA and KcD for Use With Equations RO-6 and RO-7
Storm Return Period
NRCS Soil Type
2-Year
5-Year
10-Year
25-Year
50-Year
100-Year
C and D
0
-0.10i + 0.11
-0.18i + 0.21
-0.28i + 0.33
-0.33i + 0.40
-0.39i + 0.46
A
0
-0.08i + 0.09
-0.14i + 0.17
-0.19i + 0.24
-0.22i + 0.28
-0.25i + 0.32
The values for various catchment imperviousnesses and storm return periods are presented graphically in
Figures RO-6 through RO-8, and are tabulated in Table RO-5. These coefficients were developed for the
Denver region to work in conjunction with the time of concentration recommendations in Section 2.4. Use %
of these coefficients and this procedure outside of the semi -arid climate found in the Denver region may
not be valid.
See Examples 7.1 and 7.2 that illustrate the Rational method. The use of the Rational method in storm
sewer design is illustrated in Example 6.13 of the STREETS/INLETS/STORM SEWERS chapter.
RO-10 06/2001
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1)
RUNOFF
TABLE RO-3
Recommended Percentage Imperviousness Values
Land Use or
Surface Characteristics
Percentage
Im erviousness
Business:
Commercial areas
95
Neighborhood areas
85
Residential:
Single-family
Multi -unit detached
60
Multi -unit attached
75
Half -acre lot or larger
Apartments
80
Industrial:
Light areas
80
Heavy areas
90
Parks, cemeteries
5
Playgrounds
10
Schools
50
Railroad yard areas
15
Undeveloped Areas:
Historic flow analysis
2
Greenbelts, agricultural
2
Off -site flow analysis
when land use not defined
45
Streets:
Paved
100
Gravel(packed)
40 _
Drive and walks
90 -
Roofs
90
Lawns, sandy soil
0
Lawns, clayey soil
0
See Figures RO-3 through RO-5 for percentage imperviousness.
Based in part on the data collected by the District since 1969, an empirical relationship between C and
the percentage imperviousness for various storm return periods was developed. Thus, values for C can
be determined using the following equations (Urbonas, Guo and Tucker 1990).
CA = KA + (1.31i' —1.44i z + 1.135i — 0.12) for CA >— 0, otherwise CA = 0 (RO-6)
Cco = KcD+ (0.858i' — 0.786i z + 0.774i + 0.04) (RO-7)
CB = (Ca + CcD )l2
in which:
1
i = % imperviousness/100 expressed as a decimal (see Table RO-3)
06/2001
RO-9
Urban Drainage and Flood Control District
RUNOFF
DRAINAGE CRITERIA MANUAL (V. 1)
sidewalks or compacted unvegetated soils. In urban hydrology, the percentage of pervious and
impervious land is important. As urbanization occurs, the percentage of impervious area increases and
the rainfall -runoff relation changes significantly. The total amount of runoff volume normally increases,
the time to the runoff peak rate decreases, and the peak runoff rates increase as the area urbanizes.
Photograph RO-2
Urbanization (impervious area) increases runoff volumes, peak discharges, frequency of
runoff, and receiving stream degradation.
When analyzing a watershed for design purposes, the probable future percent of impervious area must
be estimated. A complete tabulation of recommended values of the total percent of imperviousness is
provided in Table RO-3 and Figures RO-3 through RO-5, the latter developed by the District after the
evolution of residential growth patterns since 1990.
2.7 Runoff Coefficient
The runoff coefficient, C, represents the integrated effects of infiltration, evaporation, retention, and
interception, all of which affect the volume of runoff. The determination of C requires judgment and
understanding on the part of the engineer.
RO-8 06/2001
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1)
in which:
RUNOFF
t, = maximum time of concentration at the first design point in an urban watershed (minutes)
L = waterway length (ft)
Equation RO-5 was developed using the rainfall -runoff data collected in the Denver region and, in
essence, represents regional "calibration" of the Rational Method.
The first design point is the point where runoff first enters the storm, sewer system. An example of
definition of first design point is provided in Figure RO-2.
Normally, Equation RO-5 will result in a lesser time of concentration at the first design point and will
govern in an urbanized watershed. For subsequent design points, the time of concentration is calculated
by accumulating the travel times in downstream drainageway reaches.
2.4.4 Minimum Time of Concentration. Should the calculations result in a t, of less than 10 minutes, it
is recommended that a minimum value of 10 minutes be used for non -urban watersheds. The minimum t.
recommended for urbanized areas should not be less than 5 minutes and if calculations indicate a lesser
value, use 5 minutes instead.
/ 2.4.5 Common Errors in Calculatinq Time of Concentration. A common mistake in urbanized areas
is to assume travel velocities that are too slow. Another common error is to not check the runoff peak
.resulting from only part of the catchment. Sometimes a lower portion of the catchment or a highly
impervious area produces a larger peak than that computed for the whole catchment. This error is most
often encountered when the catchment is long or the upper portion contains grassy parkland and the
lower portion is developed urban land.
2.5 Intensity
The rainfall intensity, I, is the average rainfall rate in inches per hour for the period of maximum rainfall of
a given recurrence frequency having a duration equal to the time of concentration.
After the design storm's recurrence frequency has been selected, a graph should be made showing
rainfall intensity versus time. The procedure for obtaining the local data and drawing such a graph is
explained and illustrated in Section 4 of the RAINFALL chapter of this Manual. The intensity for a design
point is taken from the graph or through the use of Equation RA-3 using the calculated t,.
2.6 Watershed Imperviousness
All parts of a watershed can be considered either pervious or impervious. The pervious part is that area
where water can readily infiltrate into the ground. The impervious part is the area that does not readily
allow water to infiltrate into the ground, such as areas that are paved or covered with buildings and
06/2001 RO 7
Urban Drainage and Flood Control District
RUNOFF
DRAINAGE CRITERIA MANUAL (V. 1)
L = length of overland flow (500 ft maximum for non -urban land uses, 300 ft maximum for urban
land uses)
S = average basin slope Oft)
Equation RO-3 is adequate for distances up to 500 feet. Note that, in some urban watersheds, the
overland flow time may be very small because flows quickly channelize.
2.4.2 Overland Travel Time. For catchments with overland and channelized flow, the time of
concentration needs to be considered in combination with the overland travel time, t,, which is calculated
using the hydraulic properties of the swale, ditch, or channel. For preliminary work, the overland travel
time, t,, can be estimated with the help of Figure RO-1 or the following equation (Guo 1999):
V= C,,S,wos
in which:
V= velocity (ft/sec)
C = conveyance coefficient (from Table RO-2)
S„, = watercourse slope (fUft)
TABLE RO-2
Conveyance Coefficient, C,
(RO-4)
Type of Land Surface
Conveyance Coefficient, C .. .
Heavy meadow
2.5
Tillage/field
5
Short pasture and lawns
7
Nearly bare ground
10
Grassed waterway
15
Paved areas and shallow paved swales
20
The time of concentration, t,, is then the sum of the initial flow time, t,, and the travel time, t„ as per
Equation RO-2.
2.4.3 First Design Point Time of Concentration in Urban Catchments. Using this procedure, the time
of concentration at the first design point (i.e., initial flow time, t;) in an urbanized catchment should not
exceed the time of concentration calculated using Equation RO-5.
t`=1L +10
(RO-5)
-• .
06/2001
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1)
RUNOFF
2.4 Time of Concentration
One of the basic assumptions underlying the Rational Method is that runoff is a function of the average
rainfall rate during the time required for water to flow from the most remote part of the drainage area
under consideration to the design point. However, in practice, the time of concentration can be an
empirical value that results in reasonable and acceptable peak flow calculations. The time of
concentration relationships recommended in this Manual are based in part on the rainfall -runoff data
collected in the Denver metropolitan area and are designed to work with the runoff coefficients also
recommended in this Manual. As a result, these recommendations need to be used with a great deal of
caution whenever working in areas that may differ significantly from the climate or topography found in
the Denver region.
For urban areas, the time of concentration, t,, consists of an initial time or overland flow time, t;, plus the
travel time, t„ in the storm sewer, paved gutter, roadside drainage ditch, or drainage channel. For non -
urban areas, the time of concentration consists of an overland flow time, t;, plus the time of travel in a
defined form, such as a Swale, channel, or drainageway. The travel portion, t„ of the time of
concentration can be estimated from the hydraulic properties of the storm sewer, gutter, swale, ditch, or
drainageway. Initial time, on the other hand, will vary with surface slope, depression storage, surface
cover, antecedent rainfall, and infiltration capacity of the soil, as well as distance of surface flow. The
time of concentration is represented by Equation RO-2 for both urban and non -urban areas:
t� =tj +t'
in which:
t, = time of concentration (minutes)
t, = initial or overland flow time (minutes)
t, = travel time in the ditch, channel, gutter, storm sewer, etc. (minutes)
(RO-2)
2.4.1 Initial Flow Time. The initial or overland flow time, t;, may be calculated using equation RO-3:
0.395(1.1— CS
ti — so.33
in which:
t; = initial or overland flow time (minutes)
C5 = runoff coefficient for 5-year frequency (from Table RO-5)
(RO-3)
O6/2001 RO-5
Urban Drainage and Flood Control District
RUNOFF DRAINAGE CRITERIA MANUAL (V. 1)
4. Find the rainfall intensity, I, for the design storm using the calculated t, and the rainfall intensity- ( /
duration -frequency curve. (See Section 4.0 of the RAINFALL chapter.)
5. Determine the runoff coefficient, C.
6. Calculate the peak flow rate from the watershed using Equation RO-1.
2.2 Assumptions
The basic assumptions that are often made when the Rational Method is applied are:
1. The computed maximum rate of runoff to the design point is a function of the average rainfall rate
during the time of concentration to that point.
2. The depth of rainfall used is one that occurs from the start of the storm to the time of
concentration, and the design rainfall depth -during that time period is converted to the average
rainfall intensity for that period.
3. The maximum runoff rate occurs when the entire area is contributing flow. However, this
assumption has to be modified when a more intensely developed portion of the catchment with a
shorter time of concentration produces a higher rate of maximum runoff than the entire catchment
with a longer time of concentration.
2.3 Limitations
The Rational Method is an adequate method for approximating the peak rate and total volume of runoff
from a design rainstorm in a given catchment. The greatest drawback to the Rational Method is that it
normally provides only one point on the runoff hydrograph. When the areas become complex and where
sub -catchments come together, the Rational Method will tend to overestimate the actual flow, which
results in oversizing of drainage facilities. The Rational Method provides no direct information needed to
route hydrographs through the drainage facilities. One reason the Rational Method is limited to small
areas is that good design practice requires the routing of hydrographs for larger catchments to achieve an
economic design.
Another disadvantage of the Rational Method is that with typical design procedures one normally
assumes that all of the design flow is collected at the design point and that there is no water running
overland to the next design point. However, this is not the fault of the Rational Method but of the design
procedure. The Rational Method must be modified, or another type of analysis must be used, when
analyzing an existing system that is under -designed or when analyzing the effects of a major storm on a
system designed for the minor storm.
RO-4 0612001
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1)
111P[019a
2.0 RATIONAL METHOD
For urban catchments that are not complex and are generally 160 acres or less in size, it is acceptable
that the design storm runoff be analyzed by the Rational Method. This method was introduced in 1889
and is still being used in most engineering offices in the United States. Even though this method has
frequently come under academic criticism for its simplicity, no other practical drainage design method has
evolved to such a level of general acceptance by the practicing engineer. The Rational Method properly
understood and applied can produce satisfactory results for urban storm sewer and small on -site
detention design.
2.1 Rational Formula
The Rational Method is based on the Rational Formula:
Q=CJ4
in which:
Q = the maximum rate of runoff (cis)
C = a runoff coefficient that is the ratio between the runoff volume from an area and the average
rate of rainfall depth over a given duration for that area
I = average intensity of rainfall in inches per hour for a duration equal to the time of concentration,
tc
A = area (acres)
Actually, Q has units of inches per hour per acre (in/hr/ac); however, since this rate of in/hr/ac differs from
cubic feet per second (cfs) by less than one percent, the more common units of cfs are used. The time of
concentration is typically defined as the time required for water to flow from the most remote point of the
area to the point being investigated. The time of concentration should be based upon a flow length and
path that results in a time of concentration for only a portion of the area if that portion of the catchment
produces a higher rate of runoff.
The general procedure for Rational Method calculations for a single catchment is as follows:
1. Delineate the catchment boundary. Measure its area.
2. Define the flow path from the upper -most portion of the catchment to the design point. This flow
path should be divided into reaches of similar flow type (e.g., overland flow, shallow swale flow,
gutter flow, etc.). The length and slope of each reach should be measured.
3. Determine the time of concentration, t, for the catchment.
06/2001 RO-3
Urban Drainage and Flood Control District
SECTION 5. STORM SEWERS
The tens storm sewer shall be defined as an underground system designed to transport storm water runoff to
major drainageways. This includes inlets, conduits, manholes, and all appurtenances.
A storm sewer system shall be deemed necessary whenever street capacities to carry design storm runoff are
exceeded. This includes both the initial stone and major stone runoff.
The placement of stone inlets shall be determined by a thorough analysis of the drainage area and streets
involved. These inlets shall be located where sump (low=spot) conditions exist or where street runoff -carrying
capacities are exceeded as in the previous paragraph.
Capacities of storm sewers shall be computed using Manning's equation unless designed for pressure flow and
the hydraulic gradient shall be calculated for each storm sewer system.
Storm sewers with pressure flows shall be designed to withstand the forces of such pressure in accordance with
the appropriate standards.
5.1 Frequency Of Design Runoff
52
When conditions warrant the installation of a storm sewer system, and the street runoff -carrying
capacity does not govem the design, the stone sewer shall be designed for the storm frequencies for
the specific land uses fisted in Table 5-1.
Table 5-1
STORM DRAINAGE SYSTEM DESIGN STORM FREQUENCY
tanduse
Residential:
(RE, RL, RLP, RP, ML, RM, RMP, RLM, MM, RH)
Commercial or Business Area:
BG, BL, BP, HB, C, IL, IP. IG) .................. _.._... _..
Public Buildings Area ........._.........._........ . .................
Airports ............... ....... .............................................
.
hutialDesign Storm Retum
Period(FreWency)
Rational Method For Siang Storm Sewer System
The method in this section is from the Urban Storm Drainage Criteria Manual.
2 years
10 years
10 years
5 years
The followind step-by-step procedure should be used in conjunction with Figure 5-1. This procedure is
for the average situation and variations will often be necessary to fit actual fieid conditions.
Column 1 — Determine design point location and fist. This design point should correspond to the
sub -basin illustrated on the preliminary layout map.
Column 2 — List basins meting runoff to this point which have not previously been analyzed.
Column 3 — Enter length of flow path between previous design point and design point under consid-
eration.
Column 4 — Determine the inlet time for the particular design point For the first design point on a
system the inlet time will be equal to the time of concentration. For subsequent design
points, inlet time should also be tabulated to determine if it may be of greater magnitude
than the accumulated time of concentration from upstream basins. If the inlet time ex-
ceeds the time of concentration from the upstream basin, and the area tributary to the
inlet is of sufficient magnitude, the inlet time should be substituted for time of concentra-
tion and used for this and subsequent basins. See the runoff part of this criteria for
methods of determining inlet time.
MAY 19134 5.1 DESIGN CRrTERIA
APPENDIX D
TABLES AND FIGURES
u
ROCKY MOUNTAIN ARCHERY
Emergency Overflow Spillway Sizing
LOCATION: ROCKY MOUNTAIN ARCHERY
PROJECT NO: 316-01
COMPUTATIONS BY: TDS
SUBMITTED BY: North Star Design, Inc.
DATE: 7/6/2009
Equation for flow over weir _
top of betrn
Q = cLH A + spill elevation
where C = weir coefficient = 3.1
H = overflow height
L = length of the weir 0 100 yr WSEL
Spillways will be designed with a flow depth, H = 0.05 ft <- Maximum flow depth will be 0.60" dee;
Size the spillway assuming that the pond outlet is completely clogged.
North Detention & Water Qualitv Pond
Q (100) =
3.30
cfs
Spill elev =
68.65
ft
Min top of bens elev.=
68.70
ft
Act. Top of bens elev.=
68.65
Weir length required:
L =
100.0
ft
Use L =
100.0
ft
v = 0.48 ft/s
100 yr WSEL = 68.65 ft
<- Entire lenth of the east boundry to act as the spillway
<- Maximum flow velosity, established vegetation to provide erosion prot
Riprap is not required for bank protection
Detention - Pond 1
Northstar Design, Inc
700 Automation Drive, Unit I
Windsor CO, 80550
(970) 686-6939
LOCATION:
ITEM:
COMPUTATIONS BY
SUBMITTED BY:
DATE:
WATER QUALITY POND OUTLET SIZING - NORTH POND
ROCKY MOUNTAIN ARCHERY
Pond I
TDS
North Star Design, Inc
7/6/2009
From Urban Storm Drainage Criteria Manual, June 2001
(Referenced figures are attached in Appendix D)
Use 12 -hour brim -full volume drain time for extended detention BASIN
Water Quality Capture Volume = WQCV = a * ( 0.91 * 1^3 - 1.19 * 1^2 + 0.78 * 1 )
I = Imperviousness
Required storage = WQCV / 12 * tributary drainage area
Hour Brim Full =1
6
12
24
40
a=1
0.7
0.8
0.9
1.0
MAJOR
BASIN
Trib.
area
(ac)
%, Imperv.
Req. Storage
(in. of runoff)
from Fig. SQ-2
WQCV
(ac-ft)
DwQ
(ft)
req. vol
WQCV *1.2
(ac-ft)
Pond 1
0.58
71.32
0.225
0.011
0.013
(egwrea storage = a ` ( 0.91 - 1"3 - 1.19 * I^2 + 0.78 * 1 )
Detention - Pond 1 WQCV
Northstar Design, Inc
700 Automation Drive, Unit I
Windsor CO, 80550
(970)686-6939
Proposed Water Quality - Stage/Storage
LOCATION:
ROCKY MOUNTAIN ARCHERY
PROJECT NO:
Pond 1
COMPUTATIONS BY:
TDS
SUBMITTED BY:
North Star Design
DATE:
7/6/2009
Pond 1
V = 1/3 d (A + B + sgrt(A*B))
where V = volume between contours, ft'
d = depth between contours, ft
A = surface area of contour
Required Water Quality =
Provided Water Quality =
0.013 acre-feet
0.013 acre-feet
Stage
(ft)
Surface
Area
(ft)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4967.00
0
4968.00
376
0.003
0.003
4968.50
830
0.007
0.010
4988.65
850
0.003
0.013
<-- WO Elevation
Detention - Pond 1 Stage -Storage 1
APPENDIX C
HYDRAULIC CALCULATIONS
C
North Star Design, Inc.
Windsor Co, 80550
970 686-6939
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
LOCATION: ROCKY MOUNTAIN ARCHERY July 6, 2009
DESIGN STORM: 100-YEAR DEVELOPED
COMPUTATIONS BY: TDS
SUBMITTED BY: North Star Design, Inc.
Q = CiA
DIRECT RUNOFF
REMARKS
Area
Des.
Design A
Point (ac)
C 100
tc 5
(min)
i
(in/hr)
Q
(cfs)
1
1 0.58
0.69
8.4
8.44
3.3
Page 1 of 1
North Star Design, Inc.
Windsor Co, 80550
970 686-6939
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
LOCATION: Rocky Mountain Archery
DESIGN STORM: 10-YEAR DEVELOPED July 6, 2009
COMPUTATIONS BY: TDS
SUBMITTED BY: North Star Design, Inc.
n_l;A
Area
Des.
DIRECT RUNOFF
REMARKS
Design
Point
A
(ac)
C10
tc 5
(min)
i
(in/hr)
Q
(cfs)
1
1
0.58
0.59
8.4
4.13
1.4
Page 1 of 1
North Star Design, Inc.
Windsor Co, 80550
970 686-6939
LOCATION: Rocky Mountain Archery
DESIGN STORM: All
COMPUTATIONS BI TDS
SUBMITTED BY: North Star Design, Inc.
TIME OF CONCENTRATION
TABLE 4.2
DATE: July 6, 2009
SUB -BASIN
DATA
INITIAL /OVERLAND
TIME tl
TRAVEL TIME I GUTTER OR CHANNEL FLOW
tt
tc CHECK
NON URBAN
tc CHECK FINAL
URBANIZED BASIN tc
REMARKS
BASIN
(1)
DESIGN
POINT
I Area
(ac)
(2)
Cco 5
(3)
Length
(ft)
(4)
Slope
(5)
0
(min)
1 (6)
Length
(ft)
(7)
Slope
(8)
Channel
Type
Conv
Cost
CV
Val.
(fps)
(9)
a
(min)
(10)
tc =
8 t it
(11)
Minimum
5
minutes
Total L
00
(12)
tc=(g180)t10
(min) (min)
(13) (14)
1
1
1
0.58
0.54
30
2.0%
4.4
340
0.5%
F
20.0
1.4
4.01
8.4
5.0
370
12.1 8.4
' Area not URBANIZED
tc
= t i + t i
0 5
V= C v* S w
Type of Land Surface
Heavy meadow
Type
CV
A
2.5
Tillagel8eld
B
5.0
0.395 * (I. I — CS) * �/ L
Short pasture and lawns
C
7.0
_
t
t = t + t
c r r
Nearly bare ground
D
10.0
r —
V
Grassed waterway
E
15.0
,S' 13
Paved areas and shallow paved swales
F
20.0
Page 1 of 1
North Star Design, Inc.
Windsor Co, 80550
970 686-6939
LOCATION:
ITEM:
COMPUTATIONS BY:
SUBMITTED BY:
Rocky Mountain Archery
COMPOSITE "C" CALCULATIONS
TDS
North Star Design, Inc.
Recommended % Impervious from Urban Drainage - Type C & D Soil
July 6, 2009
Type
Imperviousness
Roof
100%
Street/Conc
100%
lawn/LandScape
0%
AREA
DESIGNATION
TOTAL
AREA
(acres)
TOTAL
AREA
(sq.ft)
STREET/GONG
AREA'
(sq.ft)
ROOF
AREA"
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
COMPOSITE %
Impervious
Cc,2-YR
Cc,5-YR
Cc, 10-YR
CCD 100-YR
1
0.58
25.200
7,916
10,057
7,227
71.32%
0.50
0.54
0.59
0.69
Assumes 4000 sf roof area for each lot
CCD = KcD + (0.858i' - 0.786i2 + 0.744i - 0.04)
Page 1 of 1
II I
-------------------------------------------------------------------------------------------
PM
PF4POM AOPK4LT
PAFEUM "Fr
"MA m
BWMGmy
;--
----------- ;W�
DFIN
PROPOSM BtM.DM
FF-"7tO
PNOPOSED
EGGS aF
GRAVEL
Ir PERFgb�
PW 0 1 . =
m
-------------------
RG w MMMY
T--
II I
i
t
--------------------------------------------
E)aSTM BULDM
LEGEND
A DMP*NT PRGPERW BWNDARY
RIdIT-W-WAY Ci
B�N MI�A
5-YR RWW COEMIOENT
EASEMENT LINE
APPENDIX B
HYDROLOGIC COMPUTATIONS
10
N
SHEET 1 OF 1
DATE: 7/06/09 ROCKY MOUNTAIN ARCHERY North Star
SCALE: 1 " = 250' GOLDEN MEADOW BU81E88 design, inc.
700 Automation Drive, Unit I
DRAWN BY: TDS PARK, LOT 110 Windsor, Colorado 80550
Phone: 970-68"939
JOB NO.: 316-01 VK*M MAP Fax: 970-686-1188
S ] »I►113 M".
VICINITY MAP
7. REFERENCES
City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March
1999.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated June 2001, and Volume 3 dated September
2001.
3
Collins. A potential exists for tracking of mud onto existing streets that could then wash
into existing storm sewers. Erosion control (BMP's) has been used to mitigate this
potential for sediment transport offsite. These measures include the use of silt fence,
wattles and a construction entrance.
5.2. Specific Details
To limit the amount of sediment leaving the site several erosion control measures shall be
implemented during construction. At the location where stormwater is being discharged
into the existing drainage swale a wattle will be used to capture any sediment and to
reduce the potential for rill and gullies from forming and the perimeter of the site shall
have silt fence installed to capture any sediment from being transported offsite to
neighboring properties. A construction entrance shall be installed at the connection to .
Innovation Drive to control the mud being tracked onto the existing public streets. Any
mud being tracked on public streets is unlawful and shall be cleared on a daily basis.
6. CONCLUSIONS
6.1. Compliance with Standards
All computations completed within this report are in compliance with the City of Fort
Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage
Design Criteria Manual.
6.2. Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans,
have been designed to convey the required stormwater flows to the proposed porous
landscape detention (PLD) pond where it is filtered and then conveyed to the existing
• drainage swale. The 100 year storm event will be conveyed safely through this
development and without causing negative impacts to adjacent properties.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit will be required.
5
rate of 3.3 cfs. this translates into a calculated flow depth over the bank to be 0.60" with a
corresponding velocity of 0.48 ft/sec. As proposed this area will be landscaped with lawn
grasses and the established vegetation will have sufficient shear strength to resist erosion
potential and therefore buried riprap is not being proposed.
The PLD has been sized in accordance with the Urban Storm Drainage Criteria Manual
developed by the Urban Drainage and Flood Control District.
4.2. Specific Flow Routing
A summary of the drainage pattern within the basin is provided in the following
paragraphs. See Appendix B for additional details.
Basin 1 consists of the entire lot. This lot includes the proposed building along with
associated parking and landscape areas. Stormwater runoff sheet flows to a concrete pan
that is located near the north property line which conveys runoff to the southeastern
portion of the lot to the porous landscape detention (PLD) pond. Stormwater is allowed
in infiltrate into the sandy layer where filtration is provided prior to stormwater being
conveyed to the existing drainage swale. The PLD provides water quality and due to this
development being within the approved design "C" value, no additional detention is
being proposed. Detention for this lot is provided in the existing detention pond for the
Golden Meadows Business Park. The majority of the sediment entering the PLD will be
filtered out in the sandy layer and shall not be transported downstream to the existing
drainage conveyance system.
4.3. Drainage Summary
All onsite drainage facilities located outside of City of Fort Collins right-of-way will be
maintained by the property owner. Drainage facilities located within the City of Fort
Collins right-of-way and capturing runoff from within the right of way will be maintained
by the City of Fort Collins.
5. EROSION CONTROL
5.1. General Concept
This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort
4
3.2. Development Criteria Reference and Constraints
Runoff from this site has been routed to conform to the requirements of the City of Fort
Collins Stormwater Department. All runoff from this development is being routed
through the porous landscape detention (PLD) area to maintain a high level of water
quality being released from this lot into the existing drainage swale. Any sediment
generated by this development will be captured in the PLD prior to stormwater being
conveyed offsite.
3.3. Hydrologic Criteria
Runoff computations are prepared for the 10 year minor storm and for the 100 year major
storm frequency utilizing the Rational Method. During the 10 year minor and 100 year
major storm events runoff is conveyed to the east to the PLD and any overtopping runoff
will be conveyed to the existing storm swale. See calculations in Appendix C.
There are existing inlets located in a sump in Innovation Drive that intercepts runoff from
the right of way. These existing inlets and storm pipe will not be altered with this project.
Innovation Drive street runoff is conveyed in existing storm pipe to the south to an
existing storm swale. No existing storm sewer exist onsite.
The proposed storm conveyance system for this lot is designed to be an aboveground
system and will convey the 100 year storm event to the PLD with no ponding. This
conveyance design will provide a safe conveyance route for a 100 year storm event
without flooding onsite buildings or negatively affecting adjacent properties.
4. DRAINAGE FACILITY DESIGN
4.1. General Concept
During a storm event runoff will be conveyed to the east to the porous landscape
detention (PLD) pond, runoff will infiltrate into the ground where it is filtered prior to
being intercepted by a perforated pipe and conveyed to the existing drainage Swale in
historic flow paths. All stormwater above the capacity of the PLD will be conveyed east
over the pond banks to the existing drainage swale in historic flow routes. With the
proposed design the overflow spillway will be along the entire eastern property line. It
has been calculated that during a 100 year storm event this lot will generate a peak runoff
Per the overall Golden Meadows Business Park approved construction plans this site is
allowed to develop to a maximum "C" value of 0.70. It has been calculated that after the
improvements are constructed this lot will have a "C" value of 0.69 which is below the
approved threshold, therefore onsite detention is not being proposed.
Stormwater runoff from the developed lot will not affect neighbor properties and all
runoff within the property boundary will be conveyed in historic drainage routes.
Historic drainage paths for this development are maintained to the greatest extent
possible.
2. DRAINAGE BASIN AND SUB -BASIN
2.1. Major Basin Description
The proposed development lies within the Fox Meadows Drainage Basin as defined by
the City of Fort Collins. The City of Fort Collins requires that any new developments
shall provide water quality. This development is routing all onsite runoff to a proposed
porous landscape detention pond where it provides water quality and is then conveyed to
the existing drainage swale where runoff is transported to the existing detention pond.
This development has been designed to convey the 100 year storm event through this
development without negatively impacting this property or neighboring properties.
2.2. Sub -basin Description
Due to the entire runoff from this lot draining to a single point, this development was able
to utilize a single basin, refer to section 4.2 for the basin description. All stormwater from
this development will ultimately be discharged into the Poudre River.
3. DRAINAGE DESIGN CRITERIA
3.1. Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
Design Criteria Manual" specifications. Where applicable, the criteria established in the
"Urban Storm Drainage Criteria Manual" (UDFCD), 2001 has been used.
F1
1. GENERAL LOCATION AND DESCRIPTION
1.1. Location
Rocky Mountain Archery is located in south Fort Collins. This project is Lot 10 in the
Golden Meadows Business Park being located within the southeast one -quarter of
Section 31, Township 7 North, Range 68 West of the Sixth Principal Meridian in the
County of Larimer, State of Colorado. See the location map in Appendix A.
The project is bounded to the north and south by commercial lots, to the east by an
existing power substation owned by the City of Fort Collins, and to the West by the
existing Innovation Drive. This development is an infill development.
1.2. Description of Properly
The project consists of approximately 0.58 acre of land. Existing vegetation consists
mainly of native grasses and large Russian Olive trees that are going to be either removed
or trimmed to create a more aesthetically pleasing landscape along the northern property
line. The land currently slopes to the northeast at approximately 1.50% slope. The
proposed improvements will consist of one commercial building with associated parking
and landscape area. The use of the commercial building will be for retail sales of archery
equipment and supplies and shall have an indoor archery shooting range. Access to this
development is gained from Innovation Drive. Innovation Drive intersects Harmony
Road approximately 250 feet south of this development.
This development is located within the Fox Meadows Drainage basin. It is proposed with
this development to provide water quality using a porous landscape detention (PLD).
Runoff that enters the PLD will infiltrate into the ground and filtered through a sandy
material to provided water quality and then conveyed to a perforated pipe and routed to
the east to the existing drainage swale. Any additional runoff above the capacity of the
PLD will be conveyed over the banks and will flow to the existing drainage swale along
the east property line. Filtered runoff and any overflow runoff will be conveyed to the
existing drainage swale where it is routed to the existing detention pond as constructed
with the overall Golden Meadows Business Park. The ultimate receiving water for runoff
from this basin is the Cache La Poudre River, hereafter referred to as the Poudre River.
Stormwater is routed to the Poudre River in historic flow paths.
TABLE OF CONTENTS
TABLE OF CONTENTS............................................................................................................... iii
GENERAL LOCATION AND DESCRIPTION
1.1 Location...................................................................................................................1
1.2 Description of Property ............................................................................................I
2. DRAINAGE BASINS AND SUB -BASINS
2.1 Major Basin Description..........................................................................................2
2.2 Sub -Basin Description.............................................................................................2
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations..............................................................................................................2
3.2 Development Criteria Reference and Constraints....................................................3
3.3 Hydrologic Criteria..................................................................................................3
4. DRAINAGE FACILITY DESIGN
4.1 General Concept.......................................................................................................3
4.2 Specific Flow Routing.............................................................................................4
4.3 Drainage Summary ...................................................................................................4
5. EROSION CONTROL
5.1 General Concept......................................................................................................4
5.2 Specific Details........................................................................................................5
6. CONCLUSIONS
6.1 Compliance with Standards....................................................................................5
6.2 Drainage Concept.....................................................................................................5
7. REFERENCES....................................................................................................................6
APPENDICES
A
Vicinity Map
B
Hydrologic Computations
C
Hydraulic Calculations
D
Erosion Control Calculations
E
Tables and Figures
F
Excerpts from previous reports
iii
North Star
I*ftordesign, inc.
July 6, 2009
Wes Lamarque
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Final Drainage and Erosion Control Report for Rocky Mountain Archery
Dear Wes,
I am pleased to submit for your review and approval, this Final Drainage & Erosion Control
Report for Rocky Mountain Archery. I certify that this report for the drainage design for Rocky
Mountain Archery was prepared in accordance with the criteria in the City of Fort Collins Storm
Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions. .
Prepared by:
Troy Spraker, P.E.
Project Manager
700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone 0 970-686-1 188 Fax
FINAL DRAINAGE AND EROSION
CONTROL REPORT
ROCKY MOUNTAIN ARCHERY
Prepared for:
Kodiak Construction and Design
37126 Soaring Eagle Circle
Windsor, Co 80550
Prepared by:
North Star Design
700 Automation Drive, Unit I
Windsor, Colorado 80550
(970) 686-6939
July 6, 2009
Job Number 316-01