Question

Given the unit hydrograph data, determine the total runoff hydrograph that would result from the given hyetograph, assuming that the baseflow is equal to 20 cfs. (23 points). USE Unit hydrograph Time UH (min) (cfs/in) 0 0 15 15 30 33 45 50 60 70 75 65 90 50 105 35 120 25 135 17 150 10 165 5 180 0 Excess rainfall hyetograph Time Interval R (in) 0-30 0.35 60-90 1.66 120-150 0.40

Answer 1

The total runoff hydrograph is determined by performing a hydrograph convolution, which involves time-shifting and adding the flow rates from the unit hydrograph multiplied by the effective rainfall intervals, and then adding the constant baseflow. The answer provides an overview of this process.

Step-by-step explanation:

The student's question relates to the creation of a runoff hydrograph from a given unit hydrograph data and an excess rainfall hyetograph for a hypothetical scenario where the baseflow is set at 20 cubic feet per second (cfs). A hydrograph is a graph that shows the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The unit hydrograph represents the response of a watershed to one inch of excess rainfall occurring uniformly over that watershed for a certain period of time.

The steps to calculate the total runoff hydrograph are as follows:

1. Determine the amount of runoff contributed by each time interval from the hyetograph by multiplying the excess rainfall during that interval by the unit hydrograph values.
2. Perform a hydrograph convolution. This involves time-shifting and summing the contributions from each time interval. Since we have multiple rainfall events, perform the process for each increment of effective rainfall.
3. Add baseflow to the ordinates resulting from step 2. In this case, add 20 cfs to account for the baseflow.
4. Plot the hydrograph by marking the resulting flows against the time. This will provide a visual representation of the total runoff hydrograph for the given event.

The data provided in the question is not sufficient for providing a detailed calculation. However, the methodology described is the general approach to be taken in solving such a problem. An example of such a calculation, given more detailed data, would involve constructing a table that aligns the runoff volume increments derived from the hyetograph with the timing of the unit hydrograph, and then performing a column-wise summation.