HomeMy WebLinkAboutResolution 006-2006 RESOLUTION NO. 06-06
A RESOLUTION AMENDING THE STORM SEWER STANDARDS
OF THE CITY OF BROOKINGS
WHEREAS,the City of Brookings, SD has adopted Resolution Number 13-04 adopting
STORM SEWER STANDARDS, CITY OF BROOKING5, DATED MARCH 9, 2004,
and;
WHEREAS,the Storm Sewer Standards shall be amended as follows:
Section 1.6 Runoff Coefficient(C):
The runoff coefficient(C)represents the integrated effects of infiltration,
evaporation, retention, flow routing, and interception, a11 of which affect the time
distribution and peak rate of runoff.
The appropriate soil types can be determined by referring to the NRCS soil maps for
Brookings.
The percent imperviousness is a parameter that must be determined when calculating the
appropriate runoff coefficient. Impervious areas are places that do not readily allow water
to infiltrate into the ground, such as areas that are paved or covered with buildings,
sidewalks, roads or compacted unvegetated soils. Recommended values for
imperviousness are provided in Table 4 and Figures 1 through 3 below. As with the
values for runoff coefficients, recommended impervious values were derived from Urban
Drainage and Flood Control District's Hydrology Research Program.
Table 1. Runoff Coefficient Values for NRCS Type A Soils
Percentage
Im erviousness Desi n Storm Return Period
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year
0% 0.00 0.00 0.05 0.12 0.16 0.20
5% 0.00 0.02 0.10 0.16 0.20 0.24
10% 0.00 0.06 0.14 0.20 0.24 0.28
15% 0.02 0.10 0.17 0.23 0.27 0.3Q
20% 0.06 0.13 0.20 0.26 0.30 0.33
25% 0.09 0.16 0.23 0.29 0.32 0.35
30% 0.13 0.19 0.25 0.31 0.34 0.37
35% 0.16 0.22 0.28 0.33 0.36 0.39
40% 0.19 0.25 0.30 0.35 0.38 0.41
45% 0.22 0.27 0.33 0.37 0.40 0.43
50% 0.25 0.30 0.35 0.40 0.42 0.45
55% 0.29 0.33 0.38 0.42 0.45 0.47
60% 0.33 0.37 0.41 0.45 0.47 0.50
65% 0.37 0.41 0.45 0.49 0.51 0.53
70% 0.42 0.45 0.49 0.53 0.54 0.56
75% 0.47 0.50 0.54 0.57 0.59 0.61
80% 0.54 0.56 0.60 0.63 0.64 0.66
85% 0.61 0.63 0.66 0.69 0.70 0.72
90% 0.69 0.71 0.73 0.76 0.77 0.79
95% 0.78 0.80 0.82 0.84 0.85 0.86
100% 0.89 0.90 0.92 0.94 0.95 0.96
2
Table 2. Runoff Coefficient Values for NRCS Type B Soils
Percentage
Im erviousness Desi n Storm Return Period
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year
0% 0.02 0.08 0.15 0.25 0.30 0.35
5% 0.04 0.10 0.19 0.28 0.33 0.38
10% 0.06 0.14 0.22 0.31 0.36 0.40
15% 0.08 0.17 0.25 0.33 0.38 0.42
20% 0.12 0.20 0.27 0.35 0.40 0.44
25% 0.15 0.22 0.30 0.37 0.41 0.46
30% 0.18 0.25 0.32 0.39 0.43 0.47
35% 0.20 0.27 0.34 0.41 0.44 0.48
40% 0.23 0.30 0.36 0.42 0.46 0.50
45% 0.26 0.32 0.38 0.44 0.48 0.51
50% 0.29 0.35 0.40 0.46 0.49 0.52
55% 0.33 0.38 0.43 0.48 0.51 0.54
60% 0.37 0.41 0.46 0.51 0.54 0.56
65% 0.41 0.45 0.49 0.54 0.57 0.59
70% 0.45 0.49 0.53 0.58 0.60 0.62
75% 0.51 0.54 0.58 0.62 0.64 0.66
80% 0.57 0.59 0.63 0.66 0.68 0.70
85% 0.63 0.66 0.69 0.72 0.73 0.75
90% 0.71 0.73 0.75 0.78 0.80 0.81
95% 0.79 0.81 0.83 0.85 0.87 0.88
100% 0.89 0.90 0.92 0.94 0.95 0.96
Table 3. Runoff Coefficient Values for NRCS Type C and D Soils
Percentage
Im erviousness Desi n Storm Return Period
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year
0% 0.04 0.15 0.25 0.37 0.44 0.50
5% 0.08 0.18 0.28 0.39 0.46 0.52
10% 0.11 0.21 0.30 0.41 0.47 0.53
15% 0.14 0.24 0.32 0.43 0.49 0.54
20% 0.17 0.26 0.34 0.44 0.50 0.55
25% 0.20 0.28 0.36 0.46 0.51 0.56
30% 0.22 0.30 0.38 0.47 0.52 0.57
35% 0.25 0.33 0.40 0.48 0.53 0.57
40% 0.28 0.35 0.42 0.50 0.54 0.58
45°/a 0.31 0.37 0.44 0.51 0.55 0.59
50% 0.34 0.40 0.46 0.53 0.57 0.60
55% 0.37 0.43 0.48 0.55 0.58 0.62
60% 0.41 0.46 0.51 0.57 0.60 0.63
65% 0.45 0.49 0.54 0.59 0.62 0.65
70% 0.49 0.53 0.57 0.62 0.65 0.68
75% 0.54 0.58 0.62 0.66 0.68 0.71
80% 0.60 0.63 0.66 0.70 0.72 0.74
85% 0.66 0.68 0.71 0.75 0.77 0.79
90% 0.73 0.75 0.77 0.80 0.82 0.83
95% 0.80 0.82 0.84 0.87 0.88 0.89
100% 0.89 0.90 0.92 0.94 0.95 0.96
3
Table 4. Recommended Percentage Imperviousness Values
Land Use or Per�centage
Surfaee Characteristics lmpervi+ousness
Bu�iness:
Cammerci�l areas 95
Neighbc�rh�od areas 85
Residential:
Single-famiiy *
Multi-unit�deta�ch�d) 60
tv�ulti-unit (attached} 75
Half-�cre lot or(arger "'
Apartments 80
#ndustrial:
Light areas 80
Heavy areas 9U
Psrks, cem�teries 5
Playgra�r�ds 10
Schools 50
Railroad yard areas 15
Undevelopeci Areas_
Historic�aw analysis 2
Greenbelts, agricu�turai 2
C}ff-site f�w ana�ysis 45
(when land use not defined)
Streets:
Pa�ved 100
Gra�vel (p�cked) 40
Qriwe and walks 90
Ftoafs 90
Lawns, sandy soil a
Lawns, clayey soil U
*See Figures 1 through 3 for percentage imperviousness
4
Figure 1. Watershed Imperviousness, Single-Family Residential Ranch Style Houses
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Figure 2.Watershed Imperviousness, Single-Family Residential Split-Level Houses
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Figure 3. Watershed Imperviousness, Single-Family Residential Two-Story Houses
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NOW,THEREFORE,BE IT RESOLVED BY THE CITY OF BROOKINGS,SD that
the amendment to Resolution Number 13-04 adopting STORM SEWER STANDARDS,
CITY OF BROOKINGS, DATED MARCH 9, 2004, is hereby adopted for the City of
Brookings, with said amendment superseding the previous Section 1.6 of Resolution
Number 13-04 and shall be on file in the office of the City Clerk and City Engineer and are
available for public inspection by any interested person.
Passed this 24�'day of January 2006.
ITY + BROOKINGS
sterman, Mayor
��.�r`'�F��,�
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ornes,City Cler
7
�Ecological Resource Consultants, Inc.
Streams�Wetlands�Water Resources
35715 US Hwy. 40, Suite D204 �Evergreen, CO 80439� 303.679.4820
Memorandum
Date: January 17, 2006
To: Jackie Lanning, P.E., City Engineer
cc:
From: Troy Thompson, P.E.
Re: City of Brookings Runoff Coefficients
Ecological Resource Consultants, Inc. (ERC), at the request of the City of
Brookings (City) is in the process of reviewing and revising current City storm
water standards. The Brookings City Council adopted the current Storm Sewer
Standards on March 9, 2004. One portion of the current City storm sewer
standards that we believe is of particular interest at this time are the values
currently used for runoff coefficients.
Runoff coefficients are an empirical means of estimating the amount of runoff that
will occur given a specific storm intensity and drainage area. Runoff coefficients
are determine based on land use, ground surface characteristics, soil types and
storm return period.
Review of values in the current City storm water standards indicates that these
runoff coefficients do not account for the imperviousness of ground cover, soil type
or storm intensity are generally lower than industry and regional standards. As a
result we believe use of the currently approved runoff coefficients will
underestimate storm runoff and tend to result in increased flooding potential.
ERC recommends that the City Council adopts revised, higher runoff coefficients
for storm water standards. Recommended runoff coefficients presented below are
based on ground cover imperviousness, soil type and storm return period. These
values were derived from Urban Drainage and Flood Control District's Hydrology
Research Program. Sioux Falls and other regional municipalities use this source
for their runoff coefficients; however values recommended for Brookings are based
on research published in 2000 where values used in Sioux Falls are based on
1979 publications.