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Published byAnabel Wilkinson Modified over 6 years ago
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Guidance on Homework 5 5.1. Report Tc and R for each watershed
Input Information - Existing Conditions Subbasin Number Area (ac) L (ft) Lca (ft) Slope (ft/mi) Development % Conveyance (%) Impervious (%) SCS CN 1 1280 7000 4000 20 30 80 78 2 1485 9000 5050 10 28 18 3 1517 8750 4975 75 100 52 85 4 2752 10000 6340 60 90 Computed Information - Existing Conditions Area (mi2) L (mi) Lca (mi) C TC+R C' TC R 1.33 0.76 6.183 2.62 2.004 0.31 2.32 TOTAL 2.0 Notes Acres per square mile ft/mi 3. C computed using 4295[%DEV]^ [%CONV]^-0.967 4. TC+R computed using C(L/sqrt(slope))^0.706 5. C' computed using 2.46-([%DEV]/100)*( ). All slopes are <=20 in this case. This interpolates between 2.46 for 0 %DEV and 0.94 for 100% Dev
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5.2 Basin Model
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5.3 Frequency Storms Area reduction Concept
Partial and annual duration See HEC HMS Manual P 207
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Intensity-Duration-Frequency
IDF design curves All major cities Based on NWS data Various return periods & durations Used for drainage design of pipes & roads Used for floodplain designs - watersheds From Bedient
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Design Rainfalls Design Storm from HCFCD and NWS
Based on Statistical Analysis of Data 5, 10, 25, 50, 100 Year Events Various Durations of 6 to 24 hours Six Hour Rainfall From Bedient
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From NOAA Atlas 2 http://www. nws. noaa
CEE 3430 – Spring 2011
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From NOAA Atlas 2 http://www. nws. noaa
CEE 3430 – Spring 2011
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Realization of Frequency Storm in HEC-HMS
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5.4 Detention Pond
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5.6 Evaluating and Comparing multiple runs
10 year Storm 100 year storm Existing Det Pond Dev Dev+Det Pond Peak Flow (cfs) Time of Peak (from start in hours:min)
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