Armfield S12-MKII, Инструкция по эксплуатации

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Exercise A
33
Figure A3
During the early stages of the rainstorm, so long as no recent rain has fallen, the
ground will be able to absorb the water falling on it and add it to the ground water
already present. When all the voids are filled, the excess must flow over the surface
and enter the stream directly as surface flow. It is this surface flow first reaching the
point of concentration that produces a sharp rise in the hydrograph and this
hydrograph discontinuity can be used to separate the ground water contribution from
the direct run-off, as indicated in Figure A3. The hydrograph shown in Figure A3 is
typical for storms of duration shorter than the time of concentration of the catchment.
Procedure
Stream flow from a single storm
Before this experiment is carried out, the sand tank should be set to a slope of about
1%. Smooth the sand in the tank to give a smooth surface parallel to the top edge of
the tank, then use the sand scoop to create a channel of rectangular cross section
centrally down the length of the tank between the river inlet and the deep outlet at the
foot. The channel should be approximately 4 cm wide by 2 cm deep.
Connect the flexible piping from the overhead spray nozzles to the quick release
connector on the 3 l/min flow meter.
a. Stream Flow for a Long Duration Storm (See Figure A4)
Turn on the spray nozzles to simulate rainfall and select a rainfall flow rate of
between 1 and 3 l/min. Allow rain to fall long enough to give a steady run-off
value. Turn off the flow and record the recession limb of the hydrograph. Use
a stopwatch started (zero time) at commencement of rainfall, and read weir
discharge as frequently as necessary to show the hydrograph form.
The experiment may be repeated for different rainfall flow rates, smaller
catchment areas (by closing some of the valves to the rainfall nozzles) and for
small differences in slope.
b. Stream Flow from a Short Duration Storm (See Figure A5)
(Less (60% - 80%) than time of concentration)