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detention-report-checklistCHECKLIST FOR STORMWATER DETENTION BASIN REPORT District P-No: 1. Project summary (narrative). 2. Graphical description of the stormwater network model. 3. Table of contents. 4. Master summary, including summary table of pre-and post-construction development runoff rates. 5. Design storms summary. 6. Time of concentration calculations (broken into sheet, shallow concentrated and open channel components). 7. Curve number calculations. 8. Pond/pipe volume calculations (elevation vs. storage table). 9. Outlet structure input data, including a composite outlet summary table, elevation vs. discharge curve, and verification that the outflow pipe is not governing ponded water surface elevations. (Note: if the computer model cannot be configured to do this verification, then this analysis should be performed using an inlet control nomograph, the 100-year 24-hour peak inflow, and proposed outlet pipe diameter.) 10. Pond routing summary (inflow and outflow) for each storm. 11. Inflow vs. time curves for all frequencies. 12. Outflow vs. time curves for all frequencies. 13. 15-yr 20-min (separate sewers) or 20-yr 20-min (combined sewers) hydraulic gradeline computations for pipes entering and leaving the basin. Hydraulic calculations showing 100-year flow is conveyed to basin; calculations at ditch sections; sills of structures set above 100-yr low- flow block elevation. 14. Structural calculations for the outlet control structures (if required). 15. Drawings illustrating the detention basin, providing at minimum the grading plan and basin cross sections defining the size, shape and depth of the detention basin. At a minimum, three sections, one at each end and one in the middle of the basin will be required. 16. Drawings illustrating the outlet structure and downstream reaches, including sewer profile from the outlet to next downstream structure (minimum). Drawings should identify which openings are “on” and “off” as part of assessing “working” and “low-flow block” conditions. 17. Drainage area maps for existing and proposed conditions, showing curve numbers of discrete areas, all time of concentration flowpath components (labeled), watershed boundaries and area (acres), and watershed identification labels (labeled as identified in stormwater network model). 18. Copy of the NRCS soils map with hydrologic group defined for site. 19. Disc (CD) with working model files.