Storm Hydrograph

Factors Influencing the Storm Hydrograph 1 | Geology of catchment area | | Geology | Lag Time | Rising Limb | Peak Discharge | Recession Limb | | Permeable rocks | Long | Gentler | Low | Gentler | | Impermeable rocks | Short | Extremely steep | High | Steeper | | Permeable rocks possess more concentrated lines of weaknesses and preexisting joints that can be exploited by water. Water flow along these open cracks and pathways within the rock is encouraged, leading to increased infiltration. This will cause subsequent percolation and larger groundwater stores and baseflow, so that discharge contributed to the channel is significantly reduced. Discharge occurs via the emergence of throughflow and baseflow, hence the longer lag time owing to time taken for water to maneuver through soil particles. e.g. carboniferous limestoneConversely, impermeable rocks inhibit infiltration as water has very few openings to seep into. This means that most water would just occur as surface runoff(HOF) due to IC being easily exceeded. Thus the channel's response is often quick and adverse. e.g. Shale, well-consolidated sandstone | | 2 | Relief of the catchment area | | Relief | Lag Time | Rising Limb | Peak Discharge | Recession Limb | | Steep slopes | Short | Steeper | Higher | Steeper | | Gentle gradient | Long | Gentler | Lower | Gentler | | When the drainage basin has a steep area, rapid surface runoff is allowed to occur rapidly due to stronger force of gravity. Hence very little infiltration can occur. Also throughflow will be faster and HOF would thus occur quickly, indicating the fast response of the channel to precipitation.Gentle long slopes however allow sufficient time for infiltration to occur and substantial groundwater stores to form, hence reducing the water volume that contributes to discharge. Slower throughflow and discharge would also mean a longer lag time