What is lag time 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 is the lag time in geology?
The time between initial inundation and onset of rapid sediment accumulation is “lag time.” This interval is critical in our understanding of shoaling-upward platform cycles. When rise in sea level places the bottom below the reach of storm waves, rapid sedimentation can occur.
What is a river’s lag time?
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. Base flow – the normal discharge of the river.
What is the lag time on a hydrograph quizlet?
The delay between peak rainfall and peak discharge. The increase in river discharge as rainwater flows into the river. The decrease in river discharge as the river returns to its normal level.
What factors affect lag time?
The lag time can be short or long depending on different factors:
- 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.
- Soil type – clay soils do not drain easily and become saturated very quickly.
How is lag time calculated?
Lag time is traveling time interval required for pumping cuttings from each particular depth to surface. With certain annular volume, the lag time, normally expressed in minutes, can be determined by dividing the annular volume (bbls) by the flow rate (bbl/min).
What will affect lag time?
Slope – steep slopes lead to rapid water transfer and shorter lag times. Gentle slopes slow down water transfer making the lag time longer. Vegetation – if there is no vegetation in an area, the water runs off into the river quicker, therefore it would have a short lag time.
What is a long lag time?
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 a hydrograph in geography?
A hydrograph shows two graphs – a bar chart showing rainfall, usually from a storm and a line graph showing discharge from before, during and after the rain storm shown in the bar graph. Basically, a hydrograph shows you the ways in which a river is affected by a storm.
When meander scars are filled with water they are?
The abandoned channel is called a meander scar and if these remnants fill with water, an oxbow lake will form.
What is lag time measured in?
This is known as discharge and is given the units metres cubed per second (Cumecs). This volume varies with time during the storm as the water takes time to arrive at the main river channel from the catchment where it falls. This is called basin lag or lag time.
How does urbanization affect the time lag between rainfall and run off?
Rapid urbanization has an adverse impact on the urban rainfall-runoff processes, which may result in the increase of urban flood risk. After urbanization, the time of overland flow concentration increased while the time of river concentration decreased; the peak time did not show much difference in this study.
What is 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. However, it is generally not computed in that fashion.
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 is the lag time on a unit storm hyetograph?
Because the duration of the unit hydrograph (the duration of the unit storm hyetograph) is generally small in comparison to the time to peak of the unit hydrograph, the difference between time to peak and lag time is often small enough to be ignored and lag time is treated as the time to peak.
What does a short lag time indicate in a river discharge?
Conversely, a short lag time indicates that the precipitation is entering the river fairly quickly. The rising limb is the steep part of the discharge line that has a positive gradient, indicating that the discharge is increasing. The falling limb is the opposite showing that the discharge is falling.