What is base time in hydrograph?

Abstract: For design projects in water resources, a hydrograph is commonly used to determine the required flood volumes. The time base of a hydrograph is a crucial parameter in such studies, and its speedy and accurate determination is essential for both economic and hydrologic reasons.

What is 1hr unit hydrograph?

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. The concept of unit hydrograph is based on linear systems theory and follow the principles of superposition and proportionality.

What is time to peak in hydrograph?

Time to peak: time interval from the start of rainfall to the peak discharge.

What is runoff hydrograph?

A runoff hydrograph represents the cumulative runoff resulted from surface and sub-surface (base flow) runoff. The surface runoff or direct runoff hydrograph is obtained from the total storm hydrograph by separating the base flow.

What is base flow on a hydrograph?

What is baseflow? Baseflow is a portion of streamflow that is not directly generated from the excess rainfall during a storm event. In other words, this is the flow that would exist in the stream without the contribution of direct runoff from the rainfall.

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 does a 2 hour unit hydrograph mean?

To get a 2-hour UH, we want 1/2 inches/hour for two hours. So we have to divide the hydrograph ordinates by 2. We divided each hydrograph ordinate by two, resulting in a 2–hour Unit Hydrograph, i.e. One inch of direct runoff total from the 2 hour storm make a 1 hour UH.

What is the application of unit hydrograph?

The Unit Hydrograph (UH) technique is widely used for runoff estimation, especially for determining peak discharges. In this paper, a geomorphologically based UH has been applied. Its most remarkable characteristic is that it includes the watershed structure in its formulation.

What does hydrograph based on the day give?

The hydrograph on the basis of day gives an idea of the flood period during the month. The hydrograph on basis of month gives an idea about the dry period of the year. The unit hydrograph is a hydrograph with a volume of 1cm runoff resulting from a rainfall of specified duration and a real pattern. 6.

In which field is hydrograph applicable?

(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. Also on large areas effective rainfall is very rarely uniform at all locations, within its specified duration.

What is relation between rain and runoff?

the rainfall-runoff relationship for any rainstorm depends on the dynamic interaction between rain intensity, soil infiltration and surface storage. Runoff occurs whenever rain intensity exceeds the infiltration capacity of the soil, providing there are no physical obstructions to surface flow.

Which is the optimum duration for a hydrograph?

The unit time or unit hydrograph duration is the duration for occurrence of precipitation excess. The optimum unit time is less than 20 percent of the time interval between the beginning of runoff from a short duration, high-intensity storm and the peak discharge of the corresponding runoff. The storm duration is the actual duration of the

How is the rate of flow expressed in a hydrograph?

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).

What kind of graph is a stage hydrograph?

A hydrograph is a graph showing stage, discharge, velocity, or other properties of water flow with respect to time. When the stage is plotted against time, the graph is a stage hydrograph (which is the form of a stream gage record).

Which is the best description of a unit hydrograph?

Unit rainfall duration refers to the time period of rainfall producing runoff (rainfall excess). The unit hydrograph resulting from a six- hour excess rainfall duration is referred to as a six-hour unit hydrograph. The precipitation is assumed to occur uniformly over the entire watershed and has a uniform time distribution.