53:119 Hydrology
Unit Hydrograph Practice

The following exercise should give you some additional practice at applying the unit hydrograph concepts of (1) linearity and (2) superposition. I've kept the numbers simple so that you can focus on the procedures.

The 2-hour unit hydrograph for a watershed is:

Time (hours)	0	1	2	3	4	5	6	7
UH (cfs)	0	2	7	8	5	3	1	0

Preliminaries

1. Compute the volume of direct runoff (V_d) for the unit hydrograph (in cfs-hrs).
   
   
2. What is the rainfall excess hyetograph (1 hour time step) associated with this 2-hour unit hydrograph event?
   
   
3. Compute the S-hydrograph for the watershed. What is the value of the S-hydrograph at time t = 10 hours?
   
   

   Prediction (for each problem, you must select the appropriate t_r-UH needed to predict the DRH for the given storm)

4. Predict the direct runoff hydrograph for the following storm:

   Time (hours)	0-2	2-4
   Pe (in)	1	2

   Verify that the volume of direct runoff is correct.
   
   

5. Predict the direct runoff hydrograph for the following storm:

   Time (hours)	0-4	4-8
   Pe (in)	1	2

   Verify that the volume of direct runoff is correct.
   
   

6. Predict the direct runoff hydrograph for the following storm:

   Time (hours)	0-1	1-2	2-3
   Pe (in)	1	2	1

   Verify that the volume of direct runoff is correct.
   
   

7. Predict the direct runoff hydrograph for the following storm:

   Time (hours)	0-3	3-6	6-9
   Pe (in)	1	2	1

   Verify that the volume of direct runoff is correct.
   
   
   Some things to think about
   
   

8. Compute the 4-hour unit hydrograph using the two methods. Note the results must be the same. Verify that the volume of direct runoff is correct for a unit hydrograph.
   
   
   The solutions are available.