A peak rainfall and peak discharge are two different graphs. Lag time is the term for the difference between the peak rainfall from the peak discharge. There is a little chance of flooding if the value of the lag time is great. A lag time that is short will show that water had already reached the river channel at a fast rate. The rise in the discharge shown in a graph is called the rising limb, whereas the decrease in the discharge is called the falling limb.
Areas of large basins normally receive more precipitation than the small ones and the they have a larger runoff. A bigger size of runoff would mean that there is longer lag time as water has a longer distance to reach the river trunk. The shape of the basin that is elongated and larger produces a lower peak flow and longer lag time than a circular basin with the same size (Gillesania, 2006). The effects of the slopes are very important. The channel flow would fall faster down a steep slope therefore it produces a steeper rising limb and a shorter lag time. Considering the soil as an important factor, infiltration is greater on thick soil even if clay would act as impermeable layer. A longer lag time happens when there are more infiltration and more shallow rising limb
A fast overland flow is observed with a higher drainage density. ...Show more