1. Storm Hydrographs
By: Sofia Gastelu

2. What is it
A storm hydrograph is a way of showing how the discharge of a river can change over time in response to a rainfall event

3. What is it It is meausred in cumecs
Lag time represents the difference between peak rainfall and peak discharge
The rising limb represents the rapid increase resulting from rainfall
The peak discharge occurs when the river reaches its highest level
The falling limb is when the discharge decreases and the level falls
Base flow is the normal flow of the river

4. Factors affecting a river’s discharge
Land use
Surfaces in urban areas are impermeable, water runs into drains, gathers speed and joins rainwater from other drains then spilling into the river
In rural areas ploughing up and down hillsides creates channels which allow rainwater to reach rivers faster increasing discharge
Rock and soil type
Permeable rock and soils absorb water easier so surface run-off is rare
Impermeable rock and soils are closely packed, rainwater can’t infiltrate so water reaches the river quickly

5. Rainfall
The type + amount of rainfall affects the river’s discharge
Heavy continual rain means more water flowing into the river and antecedent rainfall is rain that has already happened. The ground is saturated so further rain will then flow as surface run-off.
Relief
Rainwater in steep slopes is likely to run straight over the surface before it can infiltrate
In gentle slopes, infiltration is more likely to happen
Weather conditions
Hot dry weather will bake the soil so when it rains the water can’t soak in, so it will run off the surface straight into the river
High temperatures increase evaporation rates from water surfaces reducing discharge
Long periods of extreme cold weather lead to frozen ground so the water can’t soak in