Guam Stormwater Spreadsheet Training: TR-55 Peak Runoff Calculation
This draft document prepared by Tyler Miller provides training on stormwater management using the TR-55 method for peak runoff calculation. It covers topics such as runoff curve numbers, determining hydrologic soil groups, land cover assessment, time of concentration calculation, and shallow flow analysis. The document includes visual aids and step-by-step instructions for implementing these techniques in stormwater management projects.
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Presentation Transcript
GUAM STORMWATER SPREADSHEET TRAINING TR 55 Peak Runoff Calculation Graphical Method Spreadsheet 11 October 2024 (DRAFT 1) Prepared by: Tyler Miller
OVERVIEW WORK FLOW Runoff Curve Number Soils Tab NRCS Web Soil Survey TR 55 Peak Runoff Calculation CNMI Manual Vol 1, Figure 2.6 Runoff Volume CNMI Manual Vol1, Figure 2.1 & 2.6 Rainfall Data from Lander, 2004 Time of Concentration and Travel Time Infiltration Basin (in progress) Detention Basin (in progress) Swales (in progress) Bioretention (in progress) Sand Filer (in progress) 2
OVERVIEW EXCEL SHEET Cyan Cells are User Input Yellow Cells are Calculated Output 3
RUNOFF CURVE NUMBER DETERMINING HSG Determine Cover Type for the Project Area by ACRE Cover Type maps can be found at the NRCS Soil Survey Change View Extent to Guam Define your project area utilizing the AOI tool Select the Soil Map Tab to see the differing soil types Determine which hydrologic soil group (HSG) each soil is delineated as in the Soils tab. 4
RUNOFF CURVE NUMBER DETERMINING LAND COVER Determine Land Cover from Satellite Imagery for Project Area and input acreage based on the HSG group. Do this for both Pre and Post Development Finalize the values by clicking the RCN_FINISH Button Final Product will be Runoff Curve Number, CN 5
TIME OF CONCENTRATION AND TRAVEL TIME SHEET AND SHALLOW FLOW If time of concentration is known enter at the bottom of the sheet If No, Determine the LENGTH, SLOPE, SURFACE type for SHEET and SHALLOW LENGTH and SLOPE can be determined from topographic data. NOTE SHEET FLOW SHOULD BE LIMITIED TO A LENGTH OF 300 FT SURFACE is determined from Table Sheet Flow Surface Codes input the LETTER and Shallow Concentrated Surface Codes (NRCS) input the code number (i.e. 1-8) 6
TIME OF CONCENTRATION AND TRAVEL TIME SHEET AND SHALLOW FLOW LENGTH and SLOPE can be determined from topographic data. For Open Channel types MANNINGS, AREA, AND WETTED PERIMTER (WP) will need to be determined Finalize the values by clicking the FINISHED Button Final Product will be Time of Concentration, Tc 7
TR 55 Drainage Area, A, Acres and Runoff Curve Number, CN is computed from the RCN Sheet Location Adjustment Factor can be determined utilizing the CNMI Manual Vol 1, Figure 2.6 Time of Concentration, Tc, (Hrs) is computed on the TofC sheet Determine Rainfall Duration, typically 24-hr 8
RUNOFF VOLUMES REGION DETERMINATION Geological Region and Water Quality Region is determined from Figure 2.1 in CNMI Manual Vol 1. Resource Designation is calculated by these inputs. Weighted CN Value is computed on the RCN sheet Storm Adjustment Factor was selected on the TR55 sheet as Location Adjustment Factor 9
