# Computing Stormwater Runoff Rates and Volumes

## Quiz Questions

 1. The actual physical processes that convert rainfall to runoff are both complex and highly variable. As such, these processes cannot be replicated mathematically with exact certainty. True False 2. Since storms have been shown to be mathematically random events, their recurrence can also be specified as an annual probability. The equation for converting between recurrence interval and annual probability is________________________ . Annual probability (in percent) = 100 * recurrence interval (in years) Annual probability (in percent) = 100/recurrence interval (in years) Annual probability (in percent) = recurrence interval (in years)/100 None of the above 3. In most circumstances, impervious areas can be considered unconnected under the following conditions? All runoff from the unconnected impervious area must be sheet flow. Upon entering the downstream pervious area, all runoff must remain as sheet flow. All discharges onto the downstream pervious surfaces must be stable and nonerosive. All of the above 4. Computation of a peak runoff rate or hydrograph will require an estimate of a drainage area’s time of concentration (Tc). In performing Tc calculations, designers should consider the following factors? Maximum sheet flow length Maximum sheet flow roughness coefficient Tc routes All of the above 5. It is virtually inevitable that a land development or redevelopment site will have a mixture of pervious and directly connected impervious surfaces, particularly under post-development conditions. True False 6. The ______________ uses an empirical linear equation to compute the peak runoff rate from a selected period of uniform rainfall intensity. Originally developed more than 100 years ago, it continues to be useful in estimating runoff from simple, relatively small drainage areas such as parking lots. Rational Method Irrational Method Relative Method Modified Rational Method 7. Can the hydrologic characteristics of the soils in the watershed and the type of surface that covers the soils affect both runoff volume and peak discharge? Yes No 8. If the peak run off rate = 4.9 cubic feet/sec and storm duration is 2 hours. What is the total runoff volume is equal to ____________? 3728 cubic feet 35280 cubic feet 3928 cubic feet 45280 cubic feet 9. What is CN refers to in NRCS Methodology? Curb Number Climate Number Curve Number Co-efficient Number 10. Rational Method is a Methodology that uses NRCS Equation? True False