Hydrographs

Question 1

What is a hydrograph?

Answer 1

Shows a rivers discharge charges in response to a precipitation event. Vertical axis is the precipitation (mm) and discharge (cumecs) , the horizontal axis is hours or days. The bar is rainfall and the line is discharge.

Question 2

What is a flashy response hydrograph?

Answer 2

Associated with ‘flash floods’ and have a steep rising limbs because rainfall has occurred in conditions that have a lot of surface run off and a short lag time but high peak discharge.

Question 3

What conditions would result in a flashy hydrograph?

Answer 3

Prolonged rainfall (soil is saturated) or a long drought (baked soil)
Clay soil (no water can penetrate)
Steep valley (water can run down), flat (no drainage)
Small river with tributaries that link to main river and swell discharge
Little vegetation to intercept precipitation 
May be a large urban area with impenetrable areas or rural with poor farming practices

Question 4

What conditions would result in a slow response hydrograph?

Answer 4

Identical rainfall will result in less steep rising limb , peak discharge is low and lag time longer, flood risk low