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157 S Industrial Park Dr-20170905iu Civil 16439 Briar Street Omaha, NE 68136-4154 LI Solutions, uc 402-895-5633 Robert Bouvia Drainage Study r 1, Q lid Lot 8 Eriksen Subdivision Blair, NE op PROJECT UNDERSTANDING Robert Bouvia is planning to build a 40' x 64' building with a crushed rock driveway to Grant Street. The lot size is 1.99 acres, of which 0.50 acres is usable for construction. The remainder of the lot is covered in wetlands. The City of Blair, NE requires that storm water runoff from the 100 year storm event on a developed condition must not exceed the historic condition. The drainage analysis for the existing site conditions was completed using the Win TR -55 Small Watershed Hydrology program developed by the Natural Resources Conservation Service (MRCS). Output data includes storm water runoff for the 5 -yr, 10 -yr, 25 -yr, 50 -yr and 100 -yr storm events. EXISTING SITE CONDITIONS From the Natural Resources Conservation Service, it was determined that the soils in this area are classified as Luton and Albatron Silty Clay. The Hydrologic Soil Group for this soil is C/D. Drainage from the site is generally from the east to the west. Storm runoff from the usable acres (0.50) will be used to design the required storage. Total area = 0.78 acres Area = 0.78 acres Brush Area = 0.72 acres Paved Street = 0.06 acres Q 100 = 4.63 cfs www.civsolutions.com zzzzzzzza �5 (�� 5 00000000 s 000�`° � o � 00 J 01 Un o cn a o CDrte-. I I w1. GQ ~CsJ1 ¢o CD p0 II II p d CD `� CD U0 � (TQ O z r"'' O CS oy � J 00 � O O � o° ~n w CD CD n °sW o. cn O z ° O O ' ~ O d CCD CD m CD C7x �] bmo . o cn WCD o p Z cncn to O ca°D ¢ C UQCD CD ~ p :z - CD CD p CD CD C� CD tn .fl O ro < w in un A' N O E En n ¢ p. d PRO ) r , CD < o 0 CD a��o°� o n �O pCLo, N �� p, Z y1�y�rn f� cn A 0 p CD rn N D C Q19 mo -� in cn z CD C o N cr ° CD CD CD N o z CD Co ATTACHMENT NO. 1 - PROPOSED SITE LAYOUT SCALE: 1"=20' ROW UNE DF GRAM STREET PLAN LEGEND c P.C. CONCRETE APPROACH (PER CITY OF BLAIR REQUIREMENTS) CRUSHED ROCK OR GRAVEL DRIVE Z o o :1 w in Z WQ� cl) 1 m M W w (n Go O 15, n _N0 LL n ddllg CN —anti—anw— SANITARY SEWER fj O I HALF SIZED DRAWING h 1 - ,AN SAN SAN SAN SAN SAN -7SAN SAN — EXISTING SITE AINAGE O TOTAL ACRES= 0.7 T - U04 \V PAVEME BRUSH/ RAfs = 0.72 -.4.63 cfs PROPOSED SITE DRAINAGE TOTAL ACRES = 0.78 ENT/BUILDING = 0.11 W=0.62 GRAVEL = 0.05 Q100 = 4.87 cfs DRAINAGE BOUNDARY kwo 0 SAN SA SAN SAN M■ R w I�- Q N rc I co w � 4653120 A IJ r Z 4603160 46M200 4603240 4603280 960 6'18"W CA 1 N S 4503000 4503090 460 080 4653120 4603160 4603200 4603240 P� w O' a �O c CD Z r/ 7 W a � MIN O Q 960 6 7'W 4603290 d CD A V1 N � r �. A 11N Z 4602960 96° 6 18" W O G1 z O 3 C — 41 Z O O y M p a 6j o 7 ti co N 3 n� rt O 3g c G Y 50 a 2S i 03 rrt z a N: o x n d r ti J '00 (D Co CT g f O C C O, K 61 C ig a CD w � 4653120 A IJ r Z 4603160 46M200 4603240 4603280 960 6'18"W CA 1 N S 4503000 4503090 460 080 4653120 4603160 4603200 4603240 P� w O' a �O c CD Z r/ 7 W a � MIN O Q 960 6 7'W 4603290 d CD A V1 N � r �. Soil Map—Washington County, Nebraska MAP LEGEND MAP INFORMATION Area of Interest (AOI) Spoil Area The soil surveys that comprise your AOI were mapped at 0 Area of Interest (AOI) Stony Spot 1:12,000. Soils 1Z Very Stony spot Warning: Soil Map may not be valid at this scale. F7 Soil Map Unit Polygons s+n Wet Spot Enlargement of maps beyond the scale of mapping can cause ! Soil Map Unit Lines misunderstanding of the detail of mapping and accuracy of soil ,� Other line placement. The maps do not show the small areas of p soil Map unit Points Special Line Features contrasting soils that could have been shown at a more detailed Special Point Features .� scale. � Blowout Water Features Streams and Canals Please rely on the bar scale on each map sheet for map Borrow Pit measurements. Transportation Clay Spot �-f t Rails Source of Map: Natural Resources Conservation Service r Closed Depression Web Soil Survey URL: N Interstate Highways Coordinate System: Web Mercator (EPSG:3857) Gravel Pit My US Routes Maps from the Web Soil Survey are based on the Web Mercator • Gravelly Spot _ Major Roads projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the ® Landfill Local Roads Albers equal-area conic projection, should be used if more Lava Flow accurate calculations of distance or area are required. . Background Marsh or swamp E�L Aerial Photography This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. ' Mine or Quarry Soil Survey Area: Washington County, Nebraska co) Miscellaneous Water Survey Area Data: Version 15, Sep 14, 2016 0 Perennial Water Soil map units are labeled (as space allows) for map scales IV Rock Outcrop 1:50,000 or larger. .Jl.- Saline Spot Date(s) aerial images were photographed: Feb 1, 2014—Nov 25, 2016 Sandy Spot The orthophoto or other base map on which the soil lines were .g� Severely Eroded spot compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor Sinkhole shifting of map unit boundaries may be evident. Slide or Slip oa Sodic Spot USDA Natural Resources Web Soil Survey 9/5/2017 Conservation Service National Cooperative Soil Survey Page 2 of 3 Soil Map—Washington County, Nebraska Map Unit Legend Washington County, Nebraska (NE177) Map Unit Symbol Map Unit Name Acres in AOI Percent of AO1 7710 Albaton silty clay, occasionally flooded 2.5 34.3% 7711 Albaton silty clay, frequently flooded 4.6 64.1% 7791 Luton silty clay, rarely flooded 0.1 1.6% Totals for Area of Interest 7.1 100.0% USDA Natural Resources Web Soil Survey 9/5/2017 Conservation Service National Cooperative Soil Survey Page 3 of 3 Map Unit Description: Albaton silty clay, occasionally flooded ---Washington County, Nebraska Washington County, Nebraska 7710—Albaton silty clay, occasionally flooded Map Unit Setting National map unit symbol. f8hr Elevation: 800 to 1,500 feet Mean annual precipitation: 28 to 30 inches Mean annual air temperature: 50 to 54 degrees F Frost -free period: 150 to 170 days Farmland classification: Not prime farmland Map Unit Composition Albaton, occasionally flooded, and similar soils: 87 percent Minor components: 13 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Albaton, Occasionally Flooded Setting Landform: Flood plains Down-slope shape: Linear Across -slope shape: Linear Parent material: Clayey alluvium Typical profile Ap - 0 to 7 inches: silty clay Cg9 - 7 to 47 inches: clay Cg2 - 47 to 65 inches: silty clay loam 2Cg3 - 65 to 80 inches: very fine sandy loam Properties and qualities Slope: 0 to 2 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Poorly drained Runoff class: High Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: About 0 to 18 inches Frequency of flooding: Occasional Frequency of ponding: None Calcium carbonate, maximum in profile: 30 percent Available water storage in profile: Moderate (about 7.0 inches) Interpretive groups Land capability classification (irrigated): 3w Land capability classification (nonirrigated): 3w Hydrologic Soil Group: C/D Ecological site: Clayey Overflow - Veg. zone 4 (R107XY069NE) Hydric soil rating: Yes USDA Natural Resources Web Soil Survey 9/5/2017 AiiiiiO Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Albaton silty clay, occasionally flooded ---Washington County, Nebraska Minor Components Onawa, occasionally flooded Percent of map unit: 13 percent Landform: Flood plains Down-slope shape: Linear Across -slope shape: Linear Ecological site: Clayey Overflow - Veg Hydric soil rating: No Data Source Information Soil Survey Area: Washington County, Nebraska Survey Area Data: Version 15, Sep 14, 2016 zone 4 (R107XY069NE) USDA Natural Resources Web Soil Survey 9/5/2017 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Albaton silty clay, frequently flooded ---Washington County, Nebraska Washington County, Nebraska 7711—Albaton silty clay, frequently flooded Map Unit Setting National map unit symbol. f8hs Elevation: 800 to 1,500 feet Mean annual precipitation: 28 to 30 inches Mean annual air temperature: 50 to 54 degrees F Frost -free period., 150 to 170 days Farmland classification: Not prime farmland Map Unit Composition Albaton, depressional, frequently flooded, and similar soils: 70 percent Minor components: 30 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Albaton, Depressional, Frequently Flooded Setting Landform: Oxbows on flood plains Down-slope shape: Concave, linear Across -slope shape: Linear Parent material: Clayey alluvium Typical profile Ap - 0 to 7 inches: silty clay Cg - 7 to 60 inches: clay Properties and qualities Slope: 0 to 1 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Very poorly drained Runoff class: Negligible Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: About 0 to 12 inches Frequency of flooding: Frequent Frequency of ponding: Frequent Calcium carbonate, maximum in profile: 30 percent Available water storage in profile: Moderate (about 6.1 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 5w Hydrologic Soil Group: C/D Ecological site: Clayey Overflow - Veg. zone 4 (R107XY069NE) Hydric soil rating: Yes u_SDA Natural Resources Web Soil Survey 9/5/2017 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Albaton silty clay, frequently flooded ---Washington County, Nebraska Minor Components Haynie, occasionally flooded Percent of map unit: 15 percent Landform: Flood plains Down-slope shape: Linear Across -slope shape: Linear Ecological site: Silty Lowland - Veg Hydric soil rating: No zone 4 (R107XY070NE) Onawet, depressional, frequently flooded Percent of map unit: 15 percent Landform: Oxbow lakes on flood plains Down-slope shape: Linear Across -slope shape: Linear Ecological site: Clayey Overflow - Veg. zone 4 (R107XY069NE) Hydric soil rating: Yes Data Source Information Soil Survey Area: Washington County, Nebraska Survey Area Data: Version 15, Sep 14, 2016 USDA Natural Resources Web Soil Survey 9/5/2017 a" Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Luton silty clay, rarely flooded ---Washington County, Nebraska Washington County, Nebraska 7791—Luton silty clay, rarely flooded Map Unit Setting National map unit symbol: f8ij Elevation: 1,000 to 1,500 feet Mean annual precipitation: 28 to 30 inches Mean annual air temperature: 50 to 54 degrees F Frost -free period: 150 to 170 days Farmland classification: Not prime farmland Map Unit Composition Luton, rarely flooded, and similar soils: 75 percent Minor components: 25 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Luton, Rarely Flooded Setting Landform: Backswamps on flood plains Down-slope shape: Concave, linear Across -slope shape: Concave, linear Parent material: Clayey alluvium Typical profile A - 0 to 12 inches: silty clay Bkg - 12 to 24 inches: silty clay Bkssyg - 24 to 33 inches: silty clay Bssyg - 33 to 43 inches: silty clay Bkyg - 43 to 50 inches: silty clay B'kg - 50 to 60 inches: silty clay Properties and qualities Slope: 0 to 2 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Poorly drained Runoff class: High Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: About 0 to 18 inches Frequency of flooding: Rare Frequency of ponding: None Calcium carbonate, maximum in profile: 15 percent Gypsum, maximum in profile: 5 percent Available waterstorage in profile: Moderate (about 6.6 inches) Interpretive groups Land capability classification (irrigated): 3w Land capability classification (nonirrigated): 3w Hydrologic Soil Group: C/D USDA Natural Resources Web Soil Survey 9/5/2017 Aiiiiiiiiiiii Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Luton silty clay, rarely flooded ---Washington County, Nebraska Ecological site: Clayey Overflow - Veg. zone 4 (R107XY069NE) Hydric soil rating: Yes Minor Components Tieville, rarely flooded Percent of map unit: 15 percent Landform: Backswamps on flood plains Down-slope shape: Concave, linear Across -slope shape: Concave, linear Ecological site: Clayey Overflow - Veg, zone 4 (R107XY069NE) Hydric soil rating: Yes Forney, rarely flooded Percent of map unit. 10 percent Landform: Backswamps, flood plains Down-slope shape: Concave, linear Across -slope shape: Concave, linear Ecological site: Clayey Overflow - Veg. zone 4 (R107XY069NE) Hydric soil rating: Yes Data Source Information Soil Survey Area: Washington County, Nebraska Survey Area Data: Version 15, Sep 14, 2016 USDA Natural Resources Web Soil Survey 9/5/2017 NO Conservation Service National Cooperative Soil Survey Page 2 of 2 Attachment No. 4 Drainage Analysis - Existing Site Conditions (7 pages) WinTR-55 Current Data Description --- Identification Data User: Dan Norman Date: 9/5/2017 Project: Robert Bouvia Bldg Units: English SubTitle: Lot 8, Eriksen Subdivision - Existing Drainage Areal Units: Acres State: Nebraska County: Washington Filename: F:\Civil Solutions\Robert Bouvia - Blair Property\Existing Site Drainage.w55 Sub -Area Data Name Description Reach Area(ac) RCN Tc -------------------------------- A1 Outlet 0.78 76 0.1 Total area: .78 (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2 -Yr 5 -Yr 10 -Yr 25 -Yr 50 -Yr 100 -Yr 1 -Yr (in) (in) (in) (in) (in) (in) (in) ------------------------------------------------------------------------------- 3.0 3.87 4.6 5.25 5.95 6.55 2.42 Storm Data Source: Washington County, NE (NRCS) Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:57 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Storm Data Rainfall Depth by Rainfall Return Period 2 -Yr 5 -Yr 10 -Yr 25 -Yr 50 -Yr 100 -Yr 1 -Yr (in) (in) (in) (in) (in) (in) (in) --------------------- - 3.0 3.87 4.6 5.25 5.95 6.55 2.42 Storm Data Source: Washington County, NE (NRCS) Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Watershed Peak Table Sub -Area Peak Flow by Rainfall Return Period or Reach 10 -Yr 25 -Yr 50 -Yr 100 -Yr Identifier (cfs) (cfs) (cfs) (cfs) -------------------------------------------------------------- SUBAREAS Al 2.66 3.30 4.01 4.63 REACHES OUTLET 2.66 3.30 4.01 4.63 WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Hydrograph Peak/Peak Time Table Sub -Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 10 -Yr 25 -Yr 50 -Yr 100 -Yr Identifier (cfs) (cfs) (cfs) (cfs) (hr) (hr) (hr) (hr) ---------------------------------------------------------------------- SUBAREAS Al 2.66 3.30 4.01 4.63 11.93 11.94. 11.93 11.93 REACHES OUTLET 2.66 3.30 4.01 4.63 WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Sub -Area Summary Table Sub -Area Drainage Time of Curve Receiving Sub -Area Identifier Area Concentration Number Reach Description (ac) (hr) ---------------------------------------------------------------------------- Al .78 0.100 76 Outlet Total Area: .78 (ac) WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Sub -Area Time of Concentration Details Sub -Area Flow Mannings's End Wetted Travel Identifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr) -------------------------------------------------------------------------------- Al SHEET 13 0.0200 0.011 0.004 SHALLOW 21 . 0.0950 0.050 0..001 SHALLOW 191 0.0209 0.050 0.023 Time of Concentration 0.1 WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Existing Drainage Washington County, Nebraska Sub -Area Land Use and Curve Number Details Sub -Area Hydrologic Sub -Area Identifier Land Use Soil Area Group (ac) ------------------------------------------------------------------------- Al Paved parking lots, roofs, driveways C .06 Pasture, grassland or range (good) C .72 Total Area / Weighted Curve Number .78 Curve Number 98 74 76 WinTR-55, Version 1.00.10 Page 1 9/5/2017 11:14:58 PM Attachment No. 5 Drainage Analysis - Proposed Site Conditions (7 pages) WinTR-55 Current Data Description Identification Data User: Dan Norman Date: 9/11/2017 Project: Robert Bouvia Bldg Units: English SubTitle: Lot 8, Eriksen Subdivision - Proposed Drainage Areal Units: Acres State: Nebraska County: Washington Filename: F:\Civil Solutions\Robert Bouvia - Blair Property\Existing Site Drainage.w55 --- Sub -Area Data --- Name Description Reach Area(ac) RCN Tc ---------------------- ----- A1 Outlet 0.78 78 0.1 Total area: .78 (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2 -Yr 5 -Yr 10 -Yr 25 -Yr 50 -Yr 100 -Yr 1 -Yr (in) (in) (in) (in) (in) (in) (in) ----------------- ----- 3.0 3.87 4.6 5.25 5.95 6.55 2.42 Storm Data Source: Washington County, NE (NRCS) Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Storm Data Rainfall Depth by Rainfall Return Period 2 -Yr 5 -Yr 10 -Yr 25 -Yr 50 -Yr 100 -Yr 1 -Yr (in) (in) (in) (in) (in) (in) (in) ------------------------------------------------------------------------------- 3.0 3.87 4.6 5.25 5.95 6.55 2.42 Storm Data Source: Rainfall Distribution Type: Dimensionless Unit Hydrograph Washington County, NE (NRCS) Type II <standard> WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Watershed Peak Table Sub -Area Peak Flow by Rainfall Return Period or Reach 10 -Yr 25 -Yr 50 -Yr 100 -Yr Identifier (cfs) (cfs) (cfs) (cfs) ------------------------------------------------------------------------- SUBAREAS Al 2.86 3.52 4.24 4.87 REACHES OUTLET 2.86 3.52 4.24 4.87 WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Hydrograph Peak/Peak Time Table Sub -Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 10 -Yr 25 -Yr 50 -Yr 100 -Yr Identifier (cfs) (cfs) (cfs) (cfs) ------------------------------------------------------------------------------ (hr) (hr) (hr) (hr) SUBAREAS Al 2.86 3.52 4.24 4.87 11.94 11.94 11.93 11.93 REACHES OUTLET 2.86 3.52 4.24 4.87 WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Sub -Area Summary Table Sub -Area Drainage Time of Curve Receiving Sub -Area Identifier Area Concentration Number Reach Description (ac) (hr) --------------------------------------------------------------------- Al .78 0.100 78 Outlet Total Area: .78 (ac) WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Sub -Area Time of Concentration Details Sub -Area Flow Mannings's Identifier/ Length Slope n (ft) (ft/ft) ----------------------------------------- Al SHEET 13 0.0200 0.011 SHALLOW 21 0.0950 0.050 SHALLOW 191 0.0209 0.050 End Wetted Travel Area Perimeter Velocity Time (sq ft) (ft) (ft/sec) (hr) 0.004 0.001 0.023 Time of Concentration 0.1 WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM Dan Norman Robert Bouvia Bldg Lot 8, Eriksen Subdivision - Proposed Drainage Washington County, Nebraska Sub -Area Land Use and Curve Number Details Sub -Area Hydrologic Identifier Land Use Soil Group -------------------------------------------------------------- Al Open space; grass cover > 75% (good) C Paved parking lots, roofs, driveways C Gravel (w/ right-of-way) C Total Area / Weighted Curve Number Sub -Area Area (ac) .62 .12 .04 .78 Curve Number 74 98 89 78 WinTR-55, Version 1.00.10 Page 1 9/11/2017 11:37:51 AM F,,igur- 2-1 *PlutEorr sof mnoff wation. 0 tp ?.- 5 3.96 u 42 3 Q Pi 1 D G, ATTACHMENT NO 6 - EXISTING SITE DIRECT RUNOFF, 100 YR STORM 1 4 6.55 � � 10 11 12 Rainfall lP), inches a 7 E. cri r u 0 4.046 0 C r.. p - I ATTACHMENT NO 7 - PROPOSED SITE DIRECT RUNOFF, 100 YR STORM 6 6.55 7 11' 12 Roinfall (P), inches ➢=i s e r�-'! f,�,r , iie::�r�� �ieienkicaai 9�a �n m suing ror rainfall and II1' ATTACHMENT NO. 8 DETENTION BASIN SZE .6. qo = 3.86 cfs, qi;= 4.06 cfs ---- _ qo/qi = 3.86/4.06 = 0.95 VsNr = 0.124 Vr = 53.33Q(A) Vr = 53.33(4.06-3.86)(0.0012) = 0.013 ac -ft. — --- - -Vs = 0.124(0.013)=-0.0016 ac -ft. - - -- - = 70 cubic feet NOTES: Q = DIFFERENCE BETWEEN EXISTING C AND PROPOSED. _ LES --- � �} � A--AREA-IN-SQUARE-MI' 'D CD STORAGE VOLUME REQUIRED = 70 C.F. -- — -- I 2 -- EXTRAPOLATED 0.124 .1 1 .4 .5 6 .i Peak inf1o,.v discharge � G fr- " (_' 1'0 -11 -TR -55, :ter'ond F[L,.,f-unv 1W)