Different factors affecting runoff

Storm characteristics:-

1)Type and nature of storms and season:-

Tropical cyclonic storms have torrential rainfall which is violent and lasts for few hours while rainfall in temperate cyclone is slow and continuous for many days with occasional heavy showers.Both types of rainfall will aid runoff after some time of it's commencement.

In india monsoon season has the maximum rainfall and hence maximum runoff while in mediterrenean climate runoff will be maximized during winter season when there is maximum rainfall in this region.However,rainfall in summer will cause less runoff than it would have been in winter.

2)Intensity:-

Low intensity rainfall storms over longer spells contributes to ground water storage and produce relatively less runoff and a high intensity storm or a smallere area covered by it increases runoff since the losses like infiltration and evaporation are less.

3)Antecedent precipitation and frequency:-

If there is a succession of storms the run off will increase due to initial wetness of the soil dueto antecedent rainfall.

4)Direction of storm movements:-

This is related to the distribution of rainfall.Maximum rainfall along the principle tract of the strom and as the storm moves towards the inland,the moisture content decreases.Example:-in lower Damodar area,precipitation is higher than it's upper part.

5)Areal extent:-

Precipitation directly falling on the streams will encourage no runoff.If the drainage basin is large and the precipitation falling far away from the streams will have less runoff due to interception storage,depression storage etc. while precipitation falling near/close by the drainage channel will have large amount of runoff.

6)Storm direction:-

Storm direction is determined by the pressure distribution........

Meteorological characteristics:-

1)Temperature:-

High temperature will support high evapo-transpiration than medium temperature .If the temperature is such that the precipitation is in the form of snow or ice then it may not lead to any runoff or may lead to delayed runoff.

2)Humidity:-If th humidity level is high over a drainage basin then less evapo transpiration is bound to take place,since,the air is saturated.Hence,if the precipitation occurs then runoff would be much higher compared to situation when humidity is low.

3)Wind velocity:-

Wind of moderate velocity with high insolation will cause more evapotranspiration and less runoff (as base flow,sub base flow).

4)Pressure variation:-

Regions with high pressure will encourage wind to blow out from the said region and vice versa,hence,there will be very little chance of precipitation to occur in a region of high pressure.

Basin characteristics:-

1)size:-Peak runoff (if measured or expressed as cumec/Km. sq.) decreases as the catchment area increases due to higher time of concentration.Greater the size of the basin greater are the chances of precipitation being stored intercepted and prevented to produce a sufficiently large amount of runoff,as expected.

2)Shape:-A fan shaped catchment area have more runoff depending on slope angle because water,(any fluid) moves from higher to lower region,due to quick draining of slope.But gentle or flat sloping land will give in to more interception by pools,tanks,reservoirs,swamps which is not possible on a steep slope.

3)Altitude:-Catchments situated at higher altitudes will receive more precipitation and yeild greater runoff.Upland catchments in humid regions have probability in hydrological path changes during storm events and in light rains and between storm events there is infiltration rather than runoff.

4)geology:-It the soil is porous in nature like gravel or sand with high percentage of coarse materials then infiltration will dominate over the runoff but clayey soils which will become plastic after getting wet after initial precipitation will encourage runoff over infiltration.

5)Land use /vegetation:-Soil compacted due to movement of animals and man,unsurfaced roadways will encourage runoff over infiltration.Ice has compacted land surface making it nearly impermeable (for example:-Pennsylvania in U.S.A.) and aiding runoff ,anthropological activities like parking cars in parking lots,buildings,paved roads have reduced the infiltration and encouraged runoff.Rocky catchments with less vegetation will produce more runoff than the catchments which are thickly vegetated.Landuse pattern arable/grass lands/forests or cultivated areas are greatly affected by surface runoff.

6)Orientation in relation to the amount of water received:-Depends on the slope facing ,landuse ,vegetation,rainfall,sunshine,slope etc.Heavy rain storms in upland catchments changes hydrological pathways favourable due to steep slopes,frequent outcropping rocks with negligible water retention and high runoff.

7)Type of drainage net:-The drainage pattern affects runoff particularly the magnitude of floods.Example:-dendritic concentration of runoff leads to maximise floods at a particular time,in trellis pattern the hydrograph is flat.

8)Proximity to ocean or to a mountain region:-If the catchment is situtaed near a mountain chain or near a sea or an ocean the the catchment depending on whetther it is situated on the windward or at the leeward side will have different hydrograph projections at different times of the year compared to those situated at continental locations far from the aforementioned to geographic features.

Storage characteristics:-

1)Depressions:-Depressions will prevent water to runoff as precipitation will get collected in depressions rather than going to stream channel.

2)Pools and lakes:-can store water and reduce runoff in the initial stage.Ground water level recharge,flood potential is reduced.

3)Stream:-If there are large number of streams then a large part of precipitation will directly fall on channels rather than joining them as runoff.

4)channels:Storage in channels will reduce flood magnitude.

5)Check dams(in gullies):-This will prevent the water from joining the channels.

6)Upstream reservoir or tanks:-Control of runoff by man made structures at the receiving point .example:-Damodar valley corporation.

7)Flood plains,swamps:-Wet points,reduces runoff and flood.

8)Ground water storage in porous deposits(aquifers):-Infiltration of surface water reduces runoff but increases ground water.Sometimes seepage of ground water from upper areas may increases runoff.