Investigation of rainfall – run off for long duration of rain

Objective

To investigate the rainfall-runoff relation of a long duration rain storm on dry catchment.

Apparatus:

1. Basic Hydrology Apparatus
2. Stopwatch

Constants:

1. Rainfall intensity=20L/min.
2. Time interval=30sec.

Graph

Plot a hydrograph between time (x-axis) and discharge (y-axis).

Procedure

1. Set the slope of hydrology apparatus as zero.
2. Make sure that the catchment is dry.
3. Turn off all the outlet valves (all four) except the one at the point of concentration (outlet valve).
4. Now set the flow at 20L/m.
5. Turn on the rain valve and allow the rain over the catchment area for as long as the discharge at the outlet (in L/s) gets constant.
6. Note the discharge in L/s for every 30s intervals.
7. Note the time for max discharge that shall be the time of concentration T_c.

Observation

Precautions

1. There should be no losses at the outlet; to ensure that keep all the four discharge valves closed.
2. Set the discharge at the assigned value not considering the back-pressure
3. Note some additional readings too, so that falling limb can be plotted