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What is lag time on a hydrograph?
Lag time – the time taken between peak rainfall and peak discharge. Rising limb – shows the increase in discharge on a hydrograph. Falling limb – shows the return of discharge to normal/base flow on a hydrograph.
What is lag in hydrology?
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 does lag time indicate?
The lag time is the time difference between the peak precipitation and and the peak discharge. A long lag time indicates that it’s taking a long time for precipitation to enter the river. Conversely, a short lag time indicates that the precipitation is entering the river fairly quickly.
What is lag time used for?
Lag time (tL) and time of concentration (Tc) are essential time parameters used in hydrological flood-flow design methods for estimating peak discharge and flood hydrograph shape. They form the basis of a number of hydrological models used among the scientists.
How do you calculate lag time?
For a given annular volume, the lag time (in minutes) can be calculated by dividing the annular volume (bbls) by the flow rate (bbl/min). When using a time value, it should be remembered that if the flow rate changes, so will the lag.
What controls the lag time on a hydrograph?
Vegetation intercepts precipitation and slows the movement of water into river channels. This increases lag time. The amount precipitation can have an affect on the storm hydrograph. Heavy storms result in more water entering the drainage basin which results in a higher discharge.
How can I get lag time?
Time = Distance / Speed The lag time here is 10 hours. So, the pattern you should note here is “the greater the distance, the longer the lag time.” The same method of calculation may be used for earthquake waves (P-waves and S-waves).
What is catchment lag?
VALUES FOR VARIOUS PARAMETERS OF RAINFALL AND RUNOFF WERE DERIVED FROM THE ANALYSIS OF RECORDS FOR FIVE SMALL CATCHMENT AREAS. LAG TIME IS DEFINED AS THE TIME BETWEEN THE CENTERS OF MASS OF EXCESS RAINFALL AND DIRECT RUNOFF.
What causes a long lag time?
Geologydischarge – if the rocks under the ground are impermeable and water cannot drain through the rock layer resulting in rapid overland flow and a shorter lag time. Permeable rocks encourage a slow transfer by groundwater flow, hence a longer lag time.
What is peak discharge?
Peak discharge is the maximum rate of flow for a given condition and is used in the design of conservation measures. Peak discharge is also referred to as peak rate of discharge or peak rate of runoff.
What is the lag time in a hydrograph?
Lag time in regards to a hydrograph, and in particular to a unit hydrograph, has a couple of different definitions, depending on what reference you use. Conceptually, it is a relation between the center of mass of the hydrograph and the center of mass of the hyetograph.
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.
When to use TC vs LAG in hydrology?
Generally used for natural basins with well defined routes for overland flow along bare earth or mowed grass roadside channels. It is similar to the Lag method but will give shorter times compared to the Lag method. Tc is broken into 3-components or segments as prescribed by TR55.
What is the lag time of a base flow?
Base flow – the normal discharge of the river. The lag time can be short or long depending on different factors. For example, if there is no vegetation in an area, the water runs off into the river quicker, therefore it would have a short lag time.