How do you calculate time of concentration?

When the drainage area consists of several different types of surfaces, time of concentration is calculated by adding the time for each type of flow along the flow path from the watershed divide to the watershed outlet. Time of concentration is generally applied only to surface runoff.

What is Kirpich formula?

Kirpich equation is an empirical equation used to determine the time of concentration in runoff hydrograph and it is given as: t = 0.0194 L 0.77 S − 0.385. Where, t = time of concentration in minutes. L = the maximum length of water travel in m.

What is time of concentration in rational method?

For a given watershed, the time of concentration is the time required for rainfall landing on the farthest point of the watershed to reach the watershed outlet. The time of concentration should be used as the duration of the design storm for calculating peak storm water runoff rate with the Rational Method equation.

What is time of concentration in rainfall?

Time of concentration is a concept used in hydrology to measure the response of a watershed to a rain event. It is defined as the time needed for water to flow from the most remote point in a watershed to the watershed outlet.

How do you calculate overland flow length?

The average length of overland flow was determined by dividing the watershed area by twice the total length of all waterways.

What is SCS method?

The SCS curve number method is a simiple, widely used and efficient method for determining the approxient amount of runoff from a rainfall even in a particular area. The curve number is based on the area’s hydrologic soil group, land use , treatment and hydrologic condition.

What is the minimum time of concentration?

5 minutes
Minimum Time of Concentration Use a minimum tc value of 5 minutes for urbanized areas and a minimum tc value of 10 minutes for areas that are not considered urban. Use minimum values even when calculations result in a lesser time of concentration.

What is inlet time?

Inlet Time: The time required for the rain in falling on the most remote point of the tributary area to flow across the ground surface along the natural drains or gutters up to inlet of sewer is called inlet time (Figure 6.1).

How does watershed shape affect time of concentration?

Shape. For equal sized watersheds, runoff decreases as overland flow length increases. This results from the increased time of concentration. Longer duration storms, needed to produce runoff from all points in watershed, have lower average intensities.

What is overland flow time?

Overland flow travel time is divided into sheet flow travel time and shallow concentrated flow travel time. The overland flow is occurring after completion of infiltration or saturation process, it is generally assumed to be turbulent even though it mostly representing laminar characteristics (Grismer, 2016).

What is time area method?

Time-area method is based on the concept of time-area histogram, i.e. a histogram of contributing catchment subareas (segmentations of the catchment). To develop a time-area histogram, the catchment’s time of concentration is divided into a number of time intervals based on the hydrology time step.