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Appendix B• APPENDIX B Storm Water System Modeling Information • Hydrologic Information for the City of Shorewood The City of Shorewood contains only one flooding source with detailed data. The flood elevation of Lake Minnetonka is shown on the FEMA Flood Insurance Rate Maps (FIRM) at elevation 931. This is inconsistent with the MCWD elevation of 931.5. The City's modeling effort did not include this water body because it extends beyond City boundaries. The 100 -year flood elevations presented in the following tables can not be compared to the FIRM because there are no elevations specified on the FIRM. • • 0 0 0 APPENDIX B Storm Water System Modeling Information L� e is HYDROLOGIC INFORMATION FOR THE CITY OF SHOREWOOD • SUBWATERSHED NAME Indicates area shown on the Subwatershed Delineation Map. The letter generally indicates a group of subwatersheds that connect to a common outlet or lake. The abbreviations used in the following tables and the watershed to which they correspond are: GB Subwatershed tributary to Gideon Bay LMAR Subwatershed tributary to Lake Mary C Subwatershed tributary to Central area SC Subwatershed tributary to South - Central area LMIN Subwatershed tributary to Lake Minnewashta NC Subwatershed tributary to North - Central area WC Subwatershed tributary to West - Central area LV Subwatershed tributary to Lake Virginia W Subwatershed tributary to West area PC Subwatershed tributary to Purgatory Creek CB Subwatershed tributary to Carson Bay LW Subwatershed tributary to Lake William SAB Subwatershed tributary to St. Albans Bay CL Subwatershed tributary to Christmas Lake GL Subwatershed tributary to Galpin Lake I Subwatershed tributary to Lake Minnetonka SUBWATERSHED DRAINAGE AREA The area that drains directly to a particular pond or major drainageway. The subwatershed boundaries are typically determined using available contour mapping. The boundaries should be, considered approximate due to the limited availability or accuracy of the contour mapping and the possibility of alteration by new construction or storm sewer projects. TIME OF CONCENTRATION (Tc) The longest travel time for a particle of water to reach a discharge point in a watershed. CURVE NUMBER (CN) The runoff curve number accounts for many major factors in hydrologic modeling. The major factors that determine the curve number are the hydrologic soil group, the type of cover present in the watershed, land use in the watershed, and antecedent moisture conditions. Other factors affecting the curve number are whether impervious surface areas outlet directly to the drainage system or whether the flow spreads over pervious areas before entering the drainage system. Highly developed urban areas with a greater percentage of impervious surface area are characterized with higher curve numbers. Rural area with land uses of rural residential and agricultural typically will have lower curve numbers. Curve numbers have a typical range of 40 to 98. • Page 1 W: \1074.06 \HydmSummary.APP.wpd PEAK RUN -OFF RATE This is the rate water is shed from a particular drainage area. It is equivalent to the inflow rate of a storm water treatment basin. RUNOFF VOLUME This is the volume of water that is shed from a particular drainage area. The volume of water for a particular watershed is dependent on the subwatershed CN and storm event precipitation. I� 1 ►►J The normal water level of the pond is the lowest controlling elevation. It is usually taken as the invert of the outlet structure or the pump control elevation and is the elevation that the pond will drain down to after a rainfall event. The NWL does not reflect the lowest elevation that may be attained naturally by infiltration, evaporation or transpiration. POND HWL The highest water level achieved in a pond as predicted by the hydrologic/hydraulic model for a 100 -year event. The model assumes that the pond elevation is equal to the NWL at the beginning of the storm event. The HWL is affected by the accuracy of the data such as drainage area, storage capacity, outlet description and condition, and runoff factors. All of these factors should be reviewed when HWL is considered critical. RECOMMENDED 100 YEAR HWL The highest water level predicted for a pond based on the 100 -year event hydrologic/ • hydraulic model data results. This elevation is recommended for ponding areas and is not representative of actual conditions without full implementation of the model parameters. PEAK OUTFLOW FROM POND The maximum discharge rate from a pond through the outlet. This normally occurs when the pond is at the HWL and it assumes the full efficiency of the outlet structure. The peak outflow rate for subwatersheds without ponding areas is based on the flowing full capacity of the discharge pipe from that subwatershed. POND OUTLET The diameter of pipe or type of structure which provides an outlet from a subwatershed or storm water storage basin. REQUIRED STORAGE The volume of water required to be retained in order to reduce the peak runoff rate to the peak outflow from the pond. This volume of water is stored in a storm water retention basin between the NWL and the HWL. AVAILABLE STORAGE The storm water storage which is currently available within a subwatershed in the form of natural wetlands and depressions. These storage values are estimates taken from topography mapping provided by the City, U.S. Geological Survey Quad Maps, or available plans for proposed ponds. Page 2 w:uU74.081HyaroSummsry.APP.wpa APPROXIMATE OVERFLOW ELEVATION The elevation at which the pond would overland overflow if the storage capacity is exceeded. This approximate elevation was determined from contour mapping. EXISTING LOW BUILDING ELEVATION This elevation was determined from the "House- Print" on the contour mapping and does not indicate low -floor or basement elevations. These elevations should be considered approximate due to possible inaccuracies in the mapping and buildings that have been constructed after the mapping was completed. 1 -YEAR EVENT A rainfall event that has a 100% chance of occurrence in a given year. The information in this table was obtained from a hydrologic/hydraulic model that utilized the Soil Conservation Service TR -20 Hydrograph Routing procedure. The 1 -year event assumed a 2.4 inch, Type II distribution, 24 -hour duration rainfall event. 100 -YEAR EVENT A rainfall event that has a 1 % chance of occurrence in a given year. The information in this table was obtained from a hydrologic/hydraulic model that utilized the Soil Conservation Service TR20 Hydrograph Routing Procedure. The 100 -year event assumed a 5.0 inch, Type II distribution, 24 -hour duration rainfall event. • • Page 3 W: \1074.08\HydmSummary.APP.wpd g '7, TIS HOREVO( D M W , IM, ESOURGE 4 5t �MANAG ,.m ,MPRE ]ENSIVE5 VATE:R "ago 7-77; -WIM TORMWATT-iER1 0 -"M DEV�"-R at " i lw BULT& gq@ g�r g rtz pw� " 1 m -Y KP PEAK PEAK AVAILABLE APPROXIMATE EXISTING LOW SUB- RUNOFF RUNOFF POND POND OUTFLOW REQUIRED STORAGE OVERFLOW BUILDING WATERSHED AREA Tc RATE VOLUME NWL HWL FROM POND POND OUTLET STORAGE (ac-ft) ELEVATION ELEVATION NUMBER (ac) (min) CN (cfs) (ac-ft) (elev.) (elev.) (cfs) (c) (ac-ft) (b) (a) (a) COMMENTS �02 o' ANY I -t 4 �4 PC 2 10.3 20 74 4.9 0.5 922.1 922.8 1.2 12" RCP - (E) 0.2 11.8 930.8 932 Anal "INT, R 2 M.- PC4 19.3 21 76 10.9 1.0 904 904.4 3.4 5'Weir - (P) 0.3 0.8 905 912 5 PC 6 183 25 78 115.0 11.0 894.8 895.5 2.0 15" RCP - (E) 16.8 250 904 904 F"M -21 5 K, N a-MV4, 0r K Alp PC8 11.8 15 76 8.3 0.6 893.7 894 0.2 12" RCP (E) 0.5 12.8 898.3 901 ZZ-- An" 1", 1 �,lli.,�,.�� PC 10 65.9 21 74 31.1 3.0 910.8 911.6 13.7 36" RGP (E) 0.7 55 920.8 922 3 77"'F o"a a 1"I'llell"'25 `30 PC 12 3 15 87 4.5 0.3 963.9 964.8 2.5 15'weir (P) 0.1 0.7 968.3 971 R HIT 1 of CBI 7.5 15 73 4.0 0.3 1000.5 1000.7 0.1 15' Weir - (E) 0.3 16 1007 N/A R Fil".,�^`,`.(' CB3 15.2 15 80 14.6 1.0 978 978.6 0.8 18" RCP (E) 0.6 6.7 984.8 987 F-1, fl 4-:40 K1 Nw, 1-1 =R CB5 13.3 25 75 6.5 0.7 975.9 976.3 0.9 21" RCP (E) 0.3 9 987.8 984 -1 11 1 11 11 � I'll, ' "--, - y �--cf" M � 2" 0 CB 7 26.3 28 71 7.8 1.0 967.8 968.4 1.2 15" RCP (P) 0.4 23 984.5 982 PSI 12% toWm"u MMA@04 NOWZ% 0 WN am"Zommm 0 V ft CB9 14.3 19 71 5.0 0.5 970 970.6 1.0 21 CMP (E) 0.2 1.1 974 9.73.5 7 "a p, CB11 1.5 10 68 0.5 0.0 979.8 980A 0.4 12" RCP (E) 0.1 0.5 991 982 411 A IN M PON u 0 i 91190 CB13 3.4 15 81 3.5 0.3 953.1 954 1.9 18" RCP (P) 0.5 2.1 963.5 956 7- vlua������ w CB15 4.9 16 70 1.8 0.2 943.9 944.1 0.2 12" RCP (E) 0.1 5.8 952.9 953 go, 41., ',q- I , , ;w" EM i r aliml ww� 01 - ' lo x � allft"A §1 " "I NOW= A- 2 4, � i wl_ I g & CB 17 4.57 20 71 1.6 0.2 984.8 985.1 0.5 12" RCP (P) 0.0 0.8 987 990 29 Ma Alp 0- MR L LW2 71.7 34 76 30.9 3.8 931.5 931.8 0.2 15" CMP (P) 5.2 88 936 939 'R M No I'M MOMM"s All a la SAB 2 16.9 28 73 6.3 0.7 986.5 986.7 0.2 9" RCP (E) 0.6 4 992 988 al W 4�-w �% WN ^0 WIN SAB 4 21.3 19 79 16.4 1.4 944 945.9 13.2 36" CMP (P) 0.2 942 956 M-11 1,011044-60M Mll 45M 40-01MO WAV goo 9 ma F M T�Wosbk , CLlA 47 30 74 18.5 2.2 947 947.3 0.5 12" RCP (P) 1.8 12.4 949 952 -10 CL2 50 16 74 28.2 2.3 933 933.2 0.1 18" RCP (P) 2.2 44 937.2 938 � 11 - -, , , , - l , '- 7 '7 5- 70 M-10 R .0, ME,, 'M u q"Ap Mw CL4 8.2 15 69 2.7 0.3 930.4 931.3 2.2 42" CMP E) 1.0 18 937.9 N/A M- WE�� lo F-s I CL 6 1 23.7 20 1 77 1 14.7 1 1.3 1 946 946.6 1 1.8 24" RCP - (E) 1 1.0 1 3.7 1 948 948 1 11:35 AM w:\1074.08\excel\hydrotabl-99 8/16/99 10:42 AM w: \1074.08 \excel\hyd rotab 1 -99 8/20/99 Note: The Outlet designation (E) is an existing outlet, (P) is a proposed outlet. PC = subwatershed tributary to Purgatory Creek CB = subwatershed tributary to Carson Bay LW = subwatershed tributary to Lake William SAB = subwatershed tributary to St. Albans Bay CL = subwatershed tributary to Christmas Lake SUBWATERSHED LABELS GL = subwatershed tributary to Galpin Lake GB = subwatershed tributary to Gideon Bay LMAR = subwatersed tributary to Lake Mary C = subwatershed tributary to Central area SC = subwatershed tributary to South - Central area LMIN = subwatershed tributary to Lake Minnewashta NC = subwatershed tributary to North - Central area WC = subwatershed tributary to West - Central area LV = subwatershed tributary to Lake Virginia W = subwatershed tributary to West area 1= subwatershed tributary to Lake Minnetonka 10:42 AM w: \1074.081excel \hydrotab 1 -99 8/20/99 a) Elevations obtained from the Cities digital topographic V contour mapping. b) Available storage values calculated to the lowest elevation of either the overflow elevation or the low building elevation. C) It is recommended the existing outlet elevations be surveyed. 1:44 PM w:11074.08\excellhydrotaBl -99 8/27/99 w:11074.08 \excel \hydrotab1 -99 1:44 PM 8/27199 1:44 PM w:\1074.08 \excel \hydrotabl -99 8127199 1:44 PM w: 1 4.08 \excel \hyd rota b 1 -99 8127/99 1:44 PM w: \1074.08 \excel \hydrotabl -99 8/27/99 a) The critical event is the 100 year -10 day snowmelt. b) Elevations obtained from the Cities digital topographic V contour mapping. c) Available storage values calculated to the lowest elevation of either the overflow elevation or the low building elevation. d) It is recommended the existing outlet elevations be surveyed. Note: The Outlet designation (E) is an existing outlet, (P) is a proposed outlet. SUBWATERSHED LABELS PC = subwatershed tributary to Purgatory Creek CB = subwatershed tributary to Carson Bay LW = subwatershed tributary to Lake William SAB = subwatershed tributary to St. Albans Bay subwatershed tributary to Christmas Lake GL = subwatershed tributary to Galpin Lake GB = subwatershed tributary to Gideon Bay LMAR = subwatersed tributary to Lake Mary C = subwatershed tributary to Central area SC = subwatershed tributary to South - Central area wAl074.08 \excel \hydrotabl -99 ndition. (1999) It is recommeded that sediment accumulation on the downstream e the culverts be removed. e wetland currently overland overflows west to LV 2. It is recommended that a sury the low building and overflow elevation be conducted. The proposed outlet alignme ration requires easment verification. Based on the topographic mapping, one ucture could be at risk of impact if the current overflow elevation is not decreased. Outlet for this basin. It is proposed that an outlet be installed to define and establish ar N'NL for this basin. LMIN = subwatershed tributary to Lake Minnewashta NC = subwatershed tributary to North - Central area WC = subwatershed tributary to West - Central area LV = subwatershed tributary to Lake Virginia W = subwatershed tributary to West area 1= subwatershed tributary to Lake Minnetonka 1:44 PM 8127199