There are two meanings for hydrographs both coming from "hydro-" meaning water, and "-graph" meaning chart. A hydrograph plots the discharge of a
riveras a function of time. This activity can be in response to episodal event such as a flood.
The discharge is measured at a certain point in a river and is typically time variant.
*Rising limb - The part of the hydrograph up to the point of peak discharge.
*Falling limb - The part of the hydrograph after the peak discharge.
*Peak discharge - The highest point on the hydrograph when there is the greatest amount of water in the river.
*Lag time - Period of time between peak rainfall and peak discharge.
Types of hydrograph can include:
urface water hydrograph
surface waterhydrology, a hydrograph is a time record of the discharge of a stream, riveror watershed outlet. Rainfallis typically the main input to a watershed and the streamflowis often considered the output of the watershed; a hydrograph is a representation of how a watershed responds to rainfall. They are used in hydrologyand water resourcesplanning.
A watershed's response to
rainfalldepends on a variety of factors which affect the shape of a hydrograph:
topographyand geology(i.e. bedrockpermeability)
*The area of a basin receiving rainfall
agriculture, urban development, forestryoperations)
rainfalland precipitation intensity and type
Vegetationtype and cover
*River conditions (e.g. dams)
*Initial conditions (e.g. the degree of saturation of the soil and aquifers)
Soilpermeability and thickness
A hydrograph is often compared to a
hyetographof the watershed.
A unit hydrograph is used to more easily represent the effect rainfall has on a particular basin. It is a hypothetical unit response of the watershed to a unit input of rainfall. This allows easy calculation of the response to any arbitrary input, by simply performing a
convolutionbetween the rain input and the unit hydrograph output.
An instantaneous unit hydrograph is a further refinement of the concept; for an IUH, the input rainfall is assumed to all take place at a discrete point in time (obviously, this isn't the case for actual rainstorms). Making this assumption can greatly simplify the analysis involved in constructing a unit hydrograph, and it is necessary for the creation of a geomorphologic instantaneous unit hydrograph.
The creation of a GIUH is possible given nothing more than topologic data for a particular drainage basin. In fact, only the number of streams of a given order, the mean length of streams of a given order, and the mean land area draining directly to streams of a given order are absolutely required (and can be estimated rather than explicitly calculated if necessary). It is therefore possible to calculate a GIUH for a basin without any data about stream height or flow, which may not always be available.
Factors affecting the hydrograph
-Soil Saturation is dependant on previous rainfall, or otherwise known as Antecedant rainfall. -The surroundings; Rural or Urban (Could be less impermeable surface, or the surface type could vary) -Vegetation type (Deforestation and amount of interception) -Steepness of surrounding land, or 'relief' land -Drainage density (Number of tributaries) -Geology (Rock Type; Impermeable=flashier hydrographs. Or Permeable) -Season dependant; Very dry weather creates a crust on the river bed. Wet winters create increase in dishcarge. -Soil Type (Clay, sand etc.) Clay would create a flashy hydrograph, but there could be a continium between the two.
ubsurface hydrology hydrograph
In subsurface hydrology (
hydrogeology), a hydrograph is a record of the water level (the observed hydraulic headin wells screened across an aquifer).
Typically, a hydrograph is recorded for monitoring of heads in aquifers during non-test conditions (e.g., to observe the seasonal fluctuations in an aquifer). When an
aquifer testis being performed, the resulting observations are typically called drawdown, since they are subtracted from pre-test levels and often only the change in water level is dealt with.
Runoff model (reservoir)
* The U.S. Geological Survey (USGS) offers [http://waterdata.usgs.gov/nwis/rt real-time streamflow data] for thousands of streams in the United States.
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