What is lag time in hydrograph?

What is lag time in hydrograph?

Abstract River basin lag time (LAG), defined as the elapsed time between the occurrence of the centroids of the effective rainfall intensity pattern and the storm runoff hydrograph, is an important factor in determining the time to peak and the peak value of the instantaneous unit hydrograph, IUH.

What is time of concentration formula?

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 do you mean by time of concentration in storm water drain?

Explanation. Time of Concentration is the time required by the entire drainage area to contribute to the runoff is called the time of concentration or time required by the most extreme point in the drainage to reach the point of interest.

What is the difference between lag time and time of concentration?

In hydrograph analysis, lag is the time interval be- tween the center of mass of the excess rainfall and the peak runoff rate (fig. 15–3). Time of concentration (Tc) is the time required for runoff to travel from the hydraulically most distant point in the watershed to the outlet.

Is lag time the same as time of concentration?

How is the time of concentration used?

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. It is a function of the topography, geology, and land use within the watershed.

What is time of concentration used for?

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 does time of concentration affect peak flow?

Urbanization usually decreases time of concentration, thereby increasing the peak discharge. However, time of concentration can be increased as a result of ponding behind small or inadequate drainage systems (including inlets and road culverts) or by reduction of land slope through grading.

What is lag time in hydrographs?

Lag is the time between the peak flow and the centroid of rainfall. Lag time defines the shape of your hydrograph when using unit hydrograph methods. The time of concentration is used generally with rational method type analysis. However, when you are routing hydrographs you need to describe the shape of the hydrograph and water mass.

What is the difference between time of concentration and lag time?

RE: time of concentration vs. lag time. Lag is the time between the peak flow and the centroid of rainfall. Lag time defines the shape of your hydrograph when using unit hydrograph methods. The time of concentration is used generally with rational method type analysis.

What is the lag time of a watershed?

It depends only on the geography of the watershed. Lag Time ( t l ): It is the time from center of mass of excess rainfall to the center of mass of direct runoff hydrograph. It represents the position of runoff hydrograph w.r.t. the rainfall causing the runoff. One estimate of lag time as given by NRCS is: t l = 0.6 × t c

What does time of concentration mean in hydrology?

Some definitions are repeated here for better understanding of the time of concentration concept. It is one of the most important concept in hydrology for accurately computing peak discharges and runoff hydrographs. HYDROGRAPH: Hydrograph is the graph of Flow vs. Time.