Question

Below is a unit hydrograph for 1 h of effective precipitation of 1 mm.

Time (h)	Ordinates (m3/s)
0	0
1	0.1
2	0.5
3	0.8
4	1.2
5	0.9
6	0.7
7	0.4
8	0.2
9	0

1. Apply the unit hydrograph to create a predicted stormflow hydrograph for a precipitation event in which 5 mm of rain falls in the first hour and 18 mm of rain falls in the second hour.

Time (h)	UHG ordinates (m3/s)	Stormflow h1 (m3/s)	Stormflow h2 (m3/s)	Total stormflow	Baseflow (m3/s)	Total flow (m3/s)
0					0.2
1					0.2
2					0.2
3					0.2
4					0.2
5					0.2
6					0.2
7					0.2
8					0.2
9					0.2
10					0.2
11					0.2

2. Apply the unit hydrograph to create a predicted stormflow hydrograph for a precipitation event in which 1 mm of rain falls over two hours.

a. create s-curve

Time (h)	Ordinates (m3/s)	Plus 1 h	Plus 2 h	Plus 3 h	Plus 4 h	Plus 5 h	Plus 6 h	Plus 7 h	Plus 8 h	Plus 9 h	Sum (S-curve ordinates)
0
1
2
3
4
5
6
7
8
9
10

b. lag s-curve by desired duration, subtract ordinates, divide by number of hours to bring back to one unit

Time (h)	S-curve ordinates	S-curve + 2 h	Difference	2-h UHG ordinates (m3/s)
0
1
2
3
4
5
6
7
8
9
10

3. Apply the 2-h unit hydrograph for a precipitation event in which 30 mm of rain falls over 2 hours

Time (h)	2h-UHG ordinates (m3/s)	Stormflow (m3/s)	Baseflow (m3/s)	Total flow (m3/s)
0			0.2
1			0.2
2			0.2
3			0.2
4			0.2
5			0.2
6			0.2
7			0.2
8			0.2
9			0.2
10			0.2

Answer 1