Higher Geography Hydrosphere Hydrographs Today I will Date

Higher Geography Hydrosphere Hydrographs Today I will: [Date] - Be able to construct and understand flood hydrographs

Higher Geography Hydrosphere What is a hydrograph? A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river. The rate of flow is typically expressed in cubic meters (m 3). They are used to show rivers respond to a flood. Hydrographs are used to help predict flooding events therefore influence implementation of flood prevention measures.

Higher Geography Hydrosphere

Higher Geography Hydrosphere

Higher Geography Hydrosphere

Basin lag time Peak flow Rising Through flow 4 1 3 2 0 b mm lim Discharge (m 3/s) on Overland flow ssi ce 2 Re limb 3 Base flow 12 24 36 48 30 72 Hours from start of rain storm

Discharge (m 3/s) 3 The discharge of the river is measured in cumecs - this stands for cubic metres per second 2 1 0 12 24 36 48 30 Hours from start of rain storm 72

Rainfall expressed in mm Discharge (m 3/s) 3 2 mm 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm

Discharge in m 3/s, as a line graph Discharge (m 3/s) 3 2 mm 4 1 3 2 0 12 24 36 48 Hours from start of rain storm 30 72

Rising Discharge (m 3/s) limb 3 The rising limb is when the normal (base) flow of the river starts to rise when run-off, ground and soil water reaches the river. 2 mm 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm

Peak flow Rising Discharge (m 3/s) limb 3 2 Peak flow is when the Maximum discharge in the river, the time when the river reaches its highest flow mm 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm

Peak flow Rising b im Discharge (m 3/s) The recession limb shows that water is still reaching the river but in decreasing amounts nl o ssi 2 ce Re limb 3 mm 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm

Basin lag time Peak flow Rising b im nl Discharge (m 3/s) o ssi ce 2 Re limb 3 mm 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm The basin lag time is the time it takes for the water to find its way to the river

Basin lag time Peak flow Rising b im nl Discharge (m 3/s) o ssi ce 2 Re limb 3 mm 4 1 3 2 0 Base flow 12 24 36 48 30 72 Hours from start of rain storm Base Flow is the normal discharge of the river

Basin lag time Overland flow Peak flow Through flow Rising Discharge (m 3/s) mm Through flow 4 3 2 0 b im nl Overland flow o ssi ce 2 Re limb 3 1 + Base flow 12 24 36 48 30 72 Hours from start of rain storm = Storm Flow

Higher Geography Hydrosphere Read the information on page 230 and 231 of the NWW Textbook. Copy the table below into your jotter and fill in the information gathered. Reasons for Differences in Flood Hydrographs LONG LAG TIME SHORT LAG TIME

Higher Geography Hydrosphere Can you label 1 to 8 accurately? 7. 1. 6. 5. 4. 2. 3. 8. River discharge (cumecs) Rainfall (mm) Peak rainfall Falling limb Rising limb Lag time Peak discharge Time