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Concept
Hydrograph
Summary
A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).
Hydrographs often relate change of precipitation to change of discharge over time. It can also refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network. Graphs are commonly used in the design of sewerage, more specifically, the design of surface water sewerage systems and combined sewers.
Discharge the rate of flow (volume per unit time) passing a specific location in a river, or other channel. The discharge is measured at a specific point in a river and is typically time variant.
Approach Segment the river flow before the storm (antecedent flow).
Rising limb The rising limb of the hydrograph, also known as concentration curve, reflects a prolonged increase in discharge from a catchment area, typically in response to a rainfall event.
Peak dischargethe highest point on the hydrograph when the rate of discharge is greatest.
Recession (or falling) limb The recession limb extends from the peak flow rate onward. The end of stormflow ( quickflow or direct runoff) and the return to groundwater-derived flow (base flow) is often taken as the point of inflection of the recession limb. The recession limb represents the withdrawal of water from the storage built up in the basin during the earlier phases of the hydrograph.
Lag-1 autocorrelation method to compare streamflow data to itself by shifting or "lagging" initial discharge dataset 1 time unit. A Lag-10 would mean the initial data is shifted 10 days, then is compared to an unshifted version of the data. Not to be confused with lag time.
Lag time the time interval from the maximum rainfall to the peak discharge.
Time to peak time interval from the start of rainfall to the peak discharge.
Time of concentration Time of concentration is the time from the end of the precipitation period to the end of the quick–response runoff in the hydrograph.
Official source
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