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Home My WebLink AboutStormwater Mgmt Plan STORMWATER MANAGEMENT PLAN RIDGEMONT AVENUE LOT SPLIT FOR JOHN MAHONEY CONSTRUCTION, INC. July 2, 1990 Prepared by VALLEY ENGINEERING CO., INC. 16670 Franklin Trail SE - suite l20C Prior Lake, MN 55372 Date: STORMWATER MANAGEMENT PLAN RIDGEMONT AVENUE LOT SPLIT FOR JOHN MAHONEY CONSTRUCTION, INC. I hereby certify that my direct supervision under the Laws of the tJ~ rl 2- .199U I JULY 2, 1990 this report was prepared by me or under and that I am a duly Registered Engineer stat~ of 'JJ;esotai,) / ~.h ~V Jll-a/lrV'-"'"f Reg. No. 11052 IfY SUMMARY AND CONCLUSIONS: John Mahoney Construction Inc. proposes to build two single-family homes on Ridgemont Avenue in Hannan 2nd Addition. Because the proposal requires a lot- split the stormwater runoff is subject to Prior Lake's Subdivision Standards. Accordingly the proposed housing development must not increase the rate of runoff from the present condition. On-site ponding is needed for this condition to be met. Calculation of the stormwater nmoff is in accordance with the "TR-55" Method. The difference in runoff before and after development is 0.57 inches for the 100 year event. It should be noted that much of the wooded area on the property must be cleared in order to construct the on-site ponds. The 100 year peak rate of runoff would increase from 1 cfs to 2 cfs without ponding. Two retention ponds are proposed as shown in the Grading and Drainage Plan. These ponds are designed to retain the runoff from a 6 inch 100 year storm. The storage volume required is 0.57 inches X 0.87 acres m 1800 cubic feet. The storage available ,in,-Itlie '.two . ponds is 1815 cubic feet. with ponding the 100 year peak runoff from the site will be 1 cfs, the same as the present condition rate. TR-55 CURVE NUMBER COMPUTATION VERSION 1.11 Project: County Subtitle: Subarea : ------------------------------------------------------------------------------- LOT SPLIT HANNAN 2ND ADD'N. SCOTT State: MN JOHN MAHONEY CONSTRUCTION PROPOSAL EXIST User: Checked: sdh Date: Date: 06-26-90 COVER DESCRIPTION A Hydrologic Soil Group BCD Acres (eN) ------------------------------------------------------------------------------- FULLY DEVELOPED URBAN AREAS (Veg Estab.) Open space (Lawns,parks etc.) Good condition; grass cover> 75% 0.04(61) OTHER AGRICULTURAL LANDS Woods good 0.83(55) Total Area (by Hydrologic Soil Group) .87 ------------------------------------------------------------------------------- SUBAREA: EXIST TOTAL DRAINAGE AREA: .87 Acres WEIGHTED CURVE NUMBER:55 ------------------------------------------------------------------------------- TR-55 CURVE NUMBER COMPUTATION VERSION 1.11 Project : County Subtitle: Subarea : LOT SPLIT HANNAN 2ND ADD'N. SCOTT State: MN JOHN MAHONEY CONSTRUCTION PROPOSAL DEVEL User: Checked: sdh Date: 06-26-90 Date: ------------------------------------------------------------------------------- COVER DESCRIPTION A Hydrologic Soil Group BCD Acres (CN) ------------------------------------------------------------------------------- FULLY DEVELOPED URBAN AREAS (Veg Estab.) Open space (Lawns.parks etc.) Good condition; grass cover> 75% 0.42(61) Impervious Areas Paved parking lots. roofs. driveways 0.16(98) OTHER AGRICULTURAL LANDS Woods good 0.29(55) Total Area (by Hydrologic Soil Group) .87 ==.:== ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- SUBAREA: DEVEL TOTAL DRAINAGE AREA: .87 Acres WEIGHTED CURVE NUMBER:66 TR-55 Tc and Tt THRU SUBAREA COMPUTATION Project: LOT SPLIT HANNAN 2ND ADD'N. County SCOTT State: MN Subtitle: JOHN MAHONEY CONSTRUCTION PROPOSAL User: sdh Checked: ______________________________ Subarea *1 - EXIST Flow Type 2 year Length Slope Surface n rain (ft) (ft/ft) code VERSION 1.11 Date: 06-26-90 Date: ----------------------------- Area (sq/ft) Wp (ft) Velocity (ft/sec) Time (hr) Sheet 2.8 160 ------------------------------------------------------------------------------- .15 I 0.433 Time of Concentration = 0.43* ______________________________ Subarea *2 - DEVEL Flow Type 2 year Length Slope Surface n rain (ft) (ft/ft) code ===== ----------------------------- Area (sq/ft) Wp (ft) Velocity (ft/sec) Time (hr) Sheet 2.8 250 ------------------------------------------------------------------------------- --- Sheet Flow Surface A Smooth Surface B Fallow (No Res.) C Cultivated < 20 % Res. D Cultivated> 20 % Res. E Grass-Range, Short .0593 F 0.343 Time of Concentration = 0.34* Codes --- F Grass, Dense G Grass, Burmuda H Woods, light I Woods. Dense * _ Generated for use by TABULAR method Shallow Concentrated Surface Codes P Paved U Unpaved ===== TR-55 TABULAR DISCHARGE METHOD VERSION 1.11 Project: LOT SPLIT HANNAN 2ND ADD'N. County SCOTT State: MN Subtitle: JOHN MAHONEY CONSTRUCTION PROPOSAL User: sdh Checked: Date: 06-26-90 Date: Total watershed area: 0.002 sq mi Rainfall type: II Frequency: 100 years __________________________ Subareas -------------------------- Area(sq mi) Rainfall(in) Curve number Runoff(in) Tc (hrs) (Used) TimeToOutlet Ia/P Time (hr) Total Flow 11.0 0 11.3 0 11.6 0 11.9 0 12.0 1 12.1 1 12.2 2 12.3 3P 12.4 3 12.5 2 12.6 1 12.7 1 12.8 0 13.0 0 13.2 0 13.4 0 13.6 0 13.8 0 14.0 0 14.3 0 14.6 0 15.0 0 15.5 0 16.0 0 16.5 0 17.0 0 17.5 0 18.0 0 19.0 0 20.0 0 22.0 0 26.0 0 P - Peak Flow EXIST 0.00 6.0 55* 1. 52 0.43* 0.40 0.00 0.27 DEVEL 0.00* 6.0 66* 2.44 0.34* 0.30 0.00 0.17 ------------- Subarea Contribution to Total Flow (cfs) ------------ EXIST DEVEL 0 0 0 0 0 0 0 0 0 1 0 1 0 2P lP 2 1 2 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 * - value(s) provided from TR-55 system routines TR-55 CURVE NUMBER COMPUTATION VERSION 1.11 Project: County Subtitle: Subarea : LOT SPLIT HANNAN SCOTT UPPER POND UPPER 2ND ADDITION State: MN User: Checked: sdh Date: 06-28-90 Date: ------------------------~------------------------------------------------------- COVER DESCRIPTION A Hydrologic Soil Group BCD Acres (eN) ------------------------------------------------------------------------------- FULLY DEVELOPED URBAN AREAS (Veg Estab.) Open space (Lawns.parks etc.) Good condition: grass cover) 75% .20(61) Impervious Areas Paved parking lots. roofs. driveways .07(98) OTHER AGRICULTURAL LANDS Woods good .05(55) Total Area (by Hydrologic Soil Group) .32 ------------------------------------------------------------------------------- SUBAREA: UPPER TOTAL DRAINAGE AREA: .32 Acres WEIGHTED CURVE NUMBER:68* ------------------------------------------------------------------------------- * _ Generated for use by GRAPHIC method TR-55 Tc and Tt THRU SUBAREA COMPUTATION VERSION 1.11 Project : LOT SPLIT HANNAN 2ND ADDITION County SCOTT State: MN Subtitle: UPPER POND User: sdh Checked: Date: 06-28-90 Date: Flow Type ------------------------------------------------------------------------------- n Area (sq/ft) Wp (ft) Velocity (ft/sec) Time (hr) 2 year rain Length (ft) ------------------------------------------------------------------------------- Sheet Sheet 2.8 50 10 --- Sheet Flow Surface A Smooth Surface B Fallow (No Res.) C Cultivated < 20 % Res. D Cultivated> 20 % Res. E Grass-Range. Short Slope (ft/ft) Surface code .15 .40 I F Codes --- F Grass. Dense G Grass. Burmuda H Woods. Light I Woods. Dense * _ Generated for use by GRAPHIC method 0.171 0.012 Time of Concentration = 0.18* ==-== Shallow Concentrated Surface Codes P Paved U Unpaved TR-55 GRAPHICAL DISCHARGE METHOD Project : LOT SPLIT HANNAN 2ND ADDITION County SCOTT State: MN Subtitle: UPPER POND Data: Drainage Area Runoff Curve Number Time of Concentration: Rainfall Type Pond and Swamp Area .32 * Acres 68 * 0.18 * Hours II NONE aa=======_=================================== I Storm Number I 1 I 2 I 3 I 1----------------------1------1------1------1 I Frequency (yrs) I 2 I 10 100 I I I I I I 24-Hr Rainfall (in) I 2.8 I 4.2 6 I I I I I I lalP Ratio I 0.34 I 0.22 0.16 I I I I I I Runoff (in) I 0.53 I 1.33 2.62 I I I I I I Unit Peak Discharge 11.078 11.203 1.256 I I (cfs/acre/in) I I 1 I I I I I Pond and Swamp Factorl 1.00 I 1.00 1.00 I I 0.0% Ponds Used 1 I I 1----------------------1------1------ ------1 I Peak Discharge (cfs) I 0 I 1 1 I ============================================= * - Value(s) provided from TR-55 system routines User: sdh Checked: VERSION 1.11 Date: 06-28-90 Date: TR-55 STORAGE VOLUME FOR DETENTION BASINS VERSION 1.11 Project: lOT SPLIT HANNAN 2ND ADDITION County SCOTT State: MN subtitle: UPPER POND User: sdh Checked: Date: 06-28-90 Date: Drainage Area: .32 Rainfall-Type: II Runoff: 2.6 inches Peak Inflow: 1.053299 Detention Basin Storage Peak Outflow: 1 cfs Acres Rainfall Frequency: 100 years cfs Volume: .019 acre-feet TR-55 CURVE NUMBER COMPUTATION VERSION 1.11 Project: County Subtitle: Subarea : LOT SPLIT SCOTT UPPER AND UPPER HANNAN 2ND ADDIN State: MN LOWER POND AREAS COMBINED User: Checked: sdh Date: 06-28-90 Date: ------------------------------------------------------------------------------- COVER DESCRIPTION A Hydrologic Soil Group BCD Acres (CN) ------------------------------------------------------------------------------- FULLV DEVELOPED URBAN AREAS (Veg Estab.) Open space (Lawns,parks etc.) Good condition; grass cover> 75% .20(61) Impervious Areas Paved parking lots, roofs, driveways .07(98) OTHER AGRICULTURAL LANDS Woods good .05(55) Total Area (by Hydrologic Soil Group) .32 ==== ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- SUBAREA: UPPER TOTAL DRAINAGE AREA: .32 Acres WEIGHTED CURVE NUMBER:68 TR-55 CURVE NUMBER COMPUTATION VERSION 1.11 Project : County Subtitle: Subarea : LOT SPLIT SCOTT UPPER AND LOWER HANNAN 2ND ADDIN State: MN LOWER POND AREAS COMBINED User: Checked: sdh Date: 06-28-90 Date: -------------------------------------------------------------------------------~ COVER DESCRIPTION A Hydrologic Soil Group BCD Acres (CN) ------------------------------------------------------------------------------- FULLY DEVELOPED URBAN AREAS (Vag Estab.) Open space (Lawns,parks etc.) Good condition; grass cover> 75% .12(61) Impervious Areas Paved parking lots, roofs, driveways .07(96) Total Area (by Hydrologic Soil Group) .19 __e;: ------------------------------------------------------------------------------- SUBAREA: LOWER TOTAL DRAINAGE AREA: .19 Acres WEIGHTED CURVE NUMBER:75 ------------------------------------------------------------------------------- TR-55 Tc and Tt THRU SUBAREA COMPUTATION VERSION 1.11 Project: LOT SPLIT HANNAN 2ND ADD'N County SCOTT State: MN Subtitle: UPPER AND LOWER POND AREAS COMBINED Flow Type 2 year rain Length (ft) ______________________________ Subarea *1 - UPPER Slope Surface n (ft/ft) code User: Checked: sdh Date: 06-28-90 Date: ----------------------------- Area (sq/ft) Wp (ft) Velocity (ft/sec) Time (hr) ------------------------------------------------------------------------------- Sheet Sheet 2.8 50 10 .15 .40 I F ______________________________ Subarea *2 - LOWER Flow Type 2 year Length Slope Surface n rain (ft) (ft/ft) code 0.171 0.012 Time of Concantratlon = 0.18* as:=== ----------------------------- Area (sq/ft) Wp (ft) Velocity (ft/sec) Time (hr) Sheet Sheet 2.8 50 10 ------------------------------------------------------------------------------- --- Sheet Flow Surface A Smooth Surface B Fallow (No Res.) C Cultivated < 20 % Res. o Cultivated> 20 % Res. E Grass-Range. Short .15 .40 I F Codes --- F Grass. Dense G Grass. Burmuda H Woods. Light I Woods. Dense * _ Generated for use by TABULAR method 0.171 0.012 Time of Concentration - 0.18* =--== Shallow Concentrated Surface Codes P Paved U Unpaved TR-55 TABULAR DISCHARGE METHOD VERSION 1.11 Project: LOT SPLIT HANNAN 2ND ADD'N User: sdh County SCOTT State: MN Checked: Subtitle: UPPER AND LOWER POND AREAS COMBINED Date: 06-28-90 Date: Total watershed area: 0.001 sq mi Rainfall type: II Frequency: 100 years -------------------------- Subareas -------------------------- UPPER LOWER Area(sq mi) 0.00'" 0.00 Rainfall(in) 6.0 6.0 Curve number 68'" 75'" Runoff(in) 2.62 3.28 Tc (hrs) 0.18'" 0.18'" (Used) 0.20 0.20 TimeToOutlet 0.00 0.00 Ia/P 0.16 0.11 Time Total ------------- (hr) Flow UPPER LOWER 11.0 0 0 0 11.3 0 0 0 11. 6 0 0 0 11.9 0 0 0 12.0 0 0 0 12.1 2P lP 1P 12.2 2 1 1 12.3 1 1 0 Subarea Contribution to Total Flow (cfs) ------------ 12.4 0 0 0 12.5 0 0 0 12.6 0 0 0 12.7 0 0 0 12.8 0 0 0 13.0 0 0 0 13.2 0 0 0 13.4 0 0 0 13.6 0 0 0 13.8 0 0 0 14.0 0 0 0 14.3 0 0 0 14.6 0 0 0 15.0 0 0 0 15.5 0 0 0 16.0 0 0 0 16.5 0 0 0 17.0 0 0 0 17.5 0 0 0 18.0 0 0 0 19.0 0 0 0 20.0 0 0 0 22.0 0 0 0 26.0 0 0 0 P - Peak Flow '" - value(s) provided from TR-55 system routines TR-55 STORAGE VOLUME FOR DETENTION BASINS Project: LOT SPLIT HANNAN 2ND ADD'N County SCOTT State: MN Subtitle: UPPER AND LOWER POND AREAS COMBINED User: sdh Checked: VERSION 1.11 Date: 06-28-90 Date: Drainage Area: .51 Acres Rainfall Frequency: 100 years Rainfall-Type: II 24-Hour Rainfall: 6 inches Runoff Curve Number: 71 Peak Inflow: 2 cfs Detention Basin Storage Volume: 1.17 inches Runoff Volume: 2.9 inches Peak Outflow: 1 cfs 970 - ,~ ' LL. ~ - ~ <) - ~ :> IU -.I '4.a (jPPtR... POND 9"8.7 - - -- 101 ,N)l t.ll 9b8~ o 9b1 n: 962.- - 9"0 ~ .. ~ ~9'3~ ~ \U ~ LOWt~ -PO N)) VOLtJ.ME. 1 () o () eN STA..6E.. vs. STO,,^C:Jt,. JOHN MA.HONt'r ~l.<Cn().v LDr S'?L,r I~ IIA.NNf4.N 2. llP Ii..... "'b b I tJ . ~I ~I I B () N FEe,..- etAB. c- STORMWATER RET'ENTlON POliO 100 YR. H.W.L. = 968.7 STORAGE = 230 cu. ft. DISCHARGE = I c.f.s. STORMWATER RETENTION PO"D 100 YR. H.W. L. = 963.0 STORAGE = 1585 cu. ft. DISCHARGE = , C .f. s. 66 · f, " " 1<'.:~:1 --- ------------------ --------"'" , " ----- HANNEN 2ND BIT D~'~~__ ~g~4_ -------~--- ----- ~ \ I 97..'7 \ ... .. lJ.J ::> 2 lJ.J :::> <t f I U o o IX) f; .~ J I [, 't'- " ..+- I . l_______ <p 987.24 i I- ::~3318'- 2 'NIL 95/.49 g o - :E lJ.J ~ a - a: I I I III .. '" ./ - - -- .--:: -- - ---- ~ ;:::::::-- - - 956 - ~ -95"~ ---31350--- ~ \/ S'/y line of lot I, Bile. If HANNEN 2ND AD~/ON ~ ",. " 966.26 1C 966. ZZ I I I I \ \ \., OVI3Z