Storm Hydrograph

Topics: Hydrology, Water, Drainage basin Pages: 6 (1747 words) Published: February 23, 2013
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 for the channel to arrive at peak discharge.| |

3| Basin Shape|
| Basin Shape| Lag Time| Rising Limb| Peak Discharge| Recession Limb| | Round | Shorter| Steeper| Higher| Steeper| | Elongated | Longer| Gentler| Lower| Gentler| | A round basin shape has, on average, broadly comparable distances of the edges of the basin to the gauging station as seen. (The distance that water has to travel from the various tributaries to the station at the main stream is generally similar.) Thus less time is taken for discharge of tributaries to accumulate and record a peak discharge level.However an elongated basin as shown will take longer time to record a peak discharge owing to the longer distance that water has to travel from the further tributaries. Even at peak discharge, due to different arrival times of stream discharge at the main stream, the highest discharge the river possesses would not be accurately recorded, thus peak discharge would be lower than expected.| |

4| Basin Size |
| Basin Size | Lag Time| Rising Limb| Peak Discharge| Recession Limb| | Large | Longer| Gentler| Higher| Steeper| | Small | Shorter| Steeper| Lower| Gentler| | A smaller basin size would mean rainfall accumulates more quickly and takes a shorter time to flow to reach the gauging station than in a larger basin where water takes longer to flow across lengthier distances. Extremely small basins may have almost immediate responses and shorter lag times.| |

5| Soil Characteristics|
| Soil Character.| Lag Time| Rising Limb| Peak Discharge| Recession Limb| | Saturated | Short| Steep| High| Steeper | | Dry | Long| Gentle| Usually lowHigh(during prolonged rainfall)| Gentler| | Saturated soil is related to high levels of antecedent moisture which means that the soil's IC is already almost reached. Thus minimal...
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