Who invented unit hydrograph?

Last Update: April 20, 2022

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Asked by: Shea Morissette Jr.
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In the 1930s, L.K. Sherman (Sherman 1932, 1940) advanced the theory of the unit hydrograph, or unit graph. The unit hydrograph procedure assumes that discharge at any time is proportional to the volume of runoff and that time factors affecting hydrograph shape are constant.

Who proposed the unit hydrograph theory?

The theory of unit-hydrograph was developed by Le-Roy K. Sherman in the year 1932. A unit hydrograph is a direct runoff hydrograph resulting from one unit (one inch or one cm) of constant intensity uniform rainfall occurring over the entire watershed.

What is unit hydrograph theory?

The role of unit hydrograph theory in the flood prediction process is to provide an estimate of streamflow that results from a given amount precipitation. A unit hydrograph shows the temporal change in flow, or discharge, per excess unit of precipitation runoff.

How is unit hydrograph derived?

By definition, Unit Hydrograph is a direct runoff hydrograph resulting from the unit depth of effective rainfall. So, the ordinates of required UH can simply be obtained by dividing the ordinates of Direct Runoff Hydrograph by the equivalent depth of total direct runoff as shown below.

What is a unit hydrograph used for?

Unit hydrographs are used to estimate flood hydrographs by multiplying each ordinate of unit hydrograph by the volume of runoff. The unit hydrograph theory is based on the principle of proportionality, such that discharge varies directly with runoff depth.

Unit Hydrograph Introduction - Definition

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What is unit hydrograph and its limitations?

Limitations of Unit Hydrograph Theory: (i) In theory, the principle of unit hydrograph is applicable to a drainage basin of any size. In practice, however, uniformly distributed effective rainfall rarely occurs on large areas. ... The limiting size of the drainage basin is considered to be 5000 km2.

How is unit hydrograph applied?

A unit hydrograph is a hydrograph resulting from one inch or one mm of rainfall falling uniformly over the total watershed area. ... A direct runoff hydrograph can be obtained by using the discrete form of convolution integral as shown below.

What are the two assumptions of unit hydrograph theory?

The unit hydrograph is a linear response function of the watershed. It assumes that the time base of the hydrograph remains constant regardless of the amount of runoff resulting from different storms with the same duration.

What does hydrograph mean?

In its simplest form, a hydrograph is a graphical representation of runoff rate against time (Figure 1). It shows the time distribution of runoff at the point of measurement or computation, reflecting the complex characteristics of the watershed by a single curve.

What is unit hydrograph helpful in Mcq?

What is unit hydrograph helpful in? Explanation: Unit hydrograph is helpful in estimating runoff from a basin for a storm of given duration. It is also helpful in predicting the expected flood flow from a catchment if rainfall intensity in the catchment is known.

What is an annual hydrograph?

An annual hydrograph method is proposed to determine EIA. This involves using existing gauged creek systems and rainfall records from rainfall gauging networks. This enables the use of available data to determine a watershed's response to rainfall throughout the year, and thereby compute a year-round EIA.

How do you plot a hydrograph?

  1. How to Create Hydrographs in Excel. (This is for Microsoft Office Excel 2007) ...
  2. Download RAW Data. • Enter Start Date and End Date if it is different from default dates of 3 days (highlighted. ...
  3. An Excel window will pop up with the RAW data: ...
  4. Highlight the data you would like to graph: ...
  5. Go to Insert→Line Graph.

What is mass curve?

A mass diagram is the plot of accumulated inflow (i.e. supply) or outflow (i.e. demand) versus time. The mass curve of supply (i.e. supply line) is, therefore, first drawn and is superimposed by the demand curve. ... Calculate and plot the cumulative demand against time, and thus plot the mass curve of demand.

What causes different Hydrographs?

Let's take a look at these different flood hydrograph dynamics.
  • Shape. A circular shaped drainage basin leads to rapid drainage whereas a long drainage basin will take time for the water to reach the river.
  • Topography & relief. ...
  • Heavy Storms. ...
  • Lengthy rainfall. ...
  • Snowfall. ...
  • Vegetation. ...
  • Rock type.

What factors affect the shape of a hydrograph?

Factors affecting the shape of a hydrograph
  • Antecedent rainfall. Heavy rain falling on a soil which is saturated from a previous period of wet weather. ...
  • Impermeable rock types. such as granite & clay - tend to have higher drainage densities. ...
  • Size of drainage basin. ...
  • Vegetation. ...
  • Urbanisation.

What is rainfall Hyetograph?

A hyetograph is a graphical representation of the distribution of rainfall intensity over time. ... The maximum intensity may not be reached as uniformly as shown in the SCS hyetographs.

What are the assumptions of unit hydrograph?


The rainfall is uniformly distribute within the specified duration. The rainfall is uniformly distribut in the whole of the catchment area. The base or time duration of the hydrograph of direct run-off due to an effective rainfall of unit duration is constant.

What are the limitations of hydrograph?

Limitations :10  The unit hydrograph theory cannot be applied to catchment areas greater than 5000 km sq.  The unit hydrograph theory cannot be applied to very small catchments with area less than 2 km sq.  This theory cannot be applied when the major portion of the storm is in the form of snow.

What are the components of hydrograph?

Following are the components of the hydrograph:
  • Rising Limb: It shows the increase in discharge from the catchment area in response to the rainfall.
  • Falling limb or Recession Limb: ...
  • Peak Discharge: ...
  • Lag Time: ...
  • Unit Hydrograph: ...
  • Storm Hydrograph: ...
  • Snyder's Synthetic Unit Hydrograph: ...
  • Annual Hydrograph:

What is purpose of mass curve?

A plotting of the cumulative values of a variable as a function of time. This is applied especially to mass curves of rainfall in storm studies, to departures of various weather elements from normal, and to streamflow data for reservoir studies.

Why flow curve is used?

One application is in the field of fluid mechanics, where a flow curve shows the relationship between the dynamic viscosity and the shear rate of a fluid. Flow curves may also be applied to pumps, in which case they illustrate the relationship between the volumetric flow rate of the pump and the pump head.

What is the use of double mass curve?

The double mass curve is used to check the consistency of many kinds of Jiydrologic data by comparing data for a single station with that of a pattern composed of the data from several other stations in the area. The double-mass curve can be used to adjust inconsistent precipitation data.

What is Hyetograph and hydrograph?

As nouns the difference between hyetograph and hydrograph

is that hyetograph is a graphical representation of rainfall over time while hydrograph is a graph of flow past a point in a river versus time.

What causes a flashy hydrograph?

Flashy hydrographs have a steep rising limb and a small lag time. This indicates the river discharge increases rapidly over a short period of time, indicating rainwater reaches the river very quickly. This means the river is more likely to flood. ... This increases lag time.