Problem 12-1

A 85-km² catchment has a 4-h concentration time, with isochrones at 1-h intervals resulting in the following time-area histogram:

Time (h)	0-1	1-2	2-3	3-4
Area (km2)	17	21	31	16

Use the time-area method to calculate the outflow hydrograph from the following storm pattern:

Time (h)	0-1	1-2	2-3	3-4	4-5	5-6
Total rainfall (cm/h)	1	2	5	4	3	1

The runoff curve number is CN = 81. Use a spreadsheet. Verify with ONLINE ROUTING 06. Note that the latter only takes effective rainfall.

Problem 12-2

Use the Clark method to derive a 2-h unit hydrograph for a catchment with the following time-area diagram:

Time (h)	0-1	1-2	2-3	3-4	4-5	5-6
Area (km2)	20	40	60	40	24	16

Use Δt = 1 h and K = 3 h. Use a spreadsheet and verify with ONLINE ROUTING 07.

Problem 12-3

Use Example 10-3 in the text (cascade of linear reservoirs) to test ONLINE ROUTING 08. Then route the effective rainfall hyetograph of Example 10-3 (with time interval Δt = 6 h) using: (a) K = 12 h and N = 4 and (b) K = 18 h and N = 5.

Problem 12-4

A 1-h unit hydrograph derived from measured data has the following ordinates:

Time (h)	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Inflow (m3/s)	0	7	22	48	60	90	74	47	28	17	10	6	4	3	2

Assuming a time of concentration t_c = 6 h, calculate the linear reservoir storage constant K in the Clark method.