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Account for the pattern shown on the storm hydrograph. 8 marks Connection between rainfall and mean daily flow. Connection between rainfall and mean daily.

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Presentation on theme: "Account for the pattern shown on the storm hydrograph. 8 marks Connection between rainfall and mean daily flow. Connection between rainfall and mean daily."— Presentation transcript:

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2 Account for the pattern shown on the storm hydrograph. 8 marks Connection between rainfall and mean daily flow. Connection between rainfall and mean daily flow. Short lag time of 1 day. Short lag time of 1 day. Peak rainfall of 34.5mm and a peak discharge of 31.6 cumecs. Peak rainfall of 34.5mm and a peak discharge of 31.6 cumecs. Likely to have impermeable rocks or soils e.g. clay which limits infiltration and increases surface runoff, speeding up the time it takes for water to reach the river channel. Likely to have impermeable rocks or soils e.g. clay which limits infiltration and increases surface runoff, speeding up the time it takes for water to reach the river channel. Since January the vegetation cover is likely to be minimal, as leaves have fallen off trees and crops will not be planted yet. This reduces interception rates and increases surface runoff. Since January the vegetation cover is likely to be minimal, as leaves have fallen off trees and crops will not be planted yet. This reduces interception rates and increases surface runoff. High drainage density, more streams will get water into river channel more quickly. High drainage density, more streams will get water into river channel more quickly. Basin shape likely to be fat and wide as water will be channelled into river more quickly and lag time reduced. Basin shape likely to be fat and wide as water will be channelled into river more quickly and lag time reduced. Steep slopes, increase surface runoff. Steep slopes, increase surface runoff.

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4 Question Points could include; Points could include; Low steady discharge (4 cumecs) until first fall of rain which shows up 5- 10hrs as a gradual increase in discharge some four hours later. Low steady discharge (4 cumecs) until first fall of rain which shows up 5- 10hrs as a gradual increase in discharge some four hours later. Continued heavier rainfall contributes to steeping of rising limb hydrograph which reaches a peak of 75 cumecs Continued heavier rainfall contributes to steeping of rising limb hydrograph which reaches a peak of 75 cumecs The river continues to flow at a high level for several hours more before falling steeply (falling limb) The river continues to flow at a high level for several hours more before falling steeply (falling limb) The later period of reduced rainfall during the evening night of 18 th dec. explains the secondary peak in discharge of 40 cumecs in the early hours of 19 th. The later period of reduced rainfall during the evening night of 18 th dec. explains the secondary peak in discharge of 40 cumecs in the early hours of 19 th. It stopped raining around midnight on the 18/19 th. This is reflected in the gradual lowering of water levels which eventually even off and almost return to the level which they were at before the rain started. It stopped raining around midnight on the 18/19 th. This is reflected in the gradual lowering of water levels which eventually even off and almost return to the level which they were at before the rain started. Explanation might include reference to lag time, the time taken for the rain water to infiltrate the soil and reach the river. Explanation might include reference to lag time, the time taken for the rain water to infiltrate the soil and reach the river.


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