Discharge Relationships within Drainage Basins Flashcards
Annual Hydrographs components
Characteristics of a river regime are influenced mostly by climate.
Mediterranean Regions- high-pressure system
in summer, producing a summer drought.- peak can be explained by snowmelt or a summer moonsoon. In contrast, winters are associated
with low-pressure systems and the resulting rain they bring, hence higher
discharges.
Precipitation Type storm hydrographs
Rain will
be available to the system very quickly = high rising limb, high peakflow. whereas
snow will delay the impact on the system; but it may
then have a dramatic effect on the hydrograph as it
may be released quickly as meltwater resulting in flooding, high overland flow and high peakflows.
Flashy Hydrograph Response
Hydrographs with very steep limbs, especially rising limbs, a high peak discharge and a short lag time.
Annual Hydrograph
displays how water levels in a river change over time and how seasonal variations in the flow of a river occur in a year.
Vegetation influence on hydrograph
High Vegetation intercepts more rainfall (in summer especially) thus it reduces the amount of overland flow, increases lag time and reduces peak flow
Flat Hydrographs
Hydrographs with gently inclined limbs, a low peak discharge and a long lag time.
Antecendent SM influence on hydrographs
If the soil is saturated or nearly saturated due to previous rain increased rainfall will result in overland flow = high peak flow= Reduced lag time
Drainage Density influence on hydrograph
High density- urban basins with network of sewers and drains respond quickly
low drainage density-long time lag
Land use
Create impermeable surfaces- increase overland flow, increase peak flow, reduce lag time
Reduce vegetation cover- increase overland flow, increase peak flow, reduce lag time
More drainage channels built- water carried to rivers quickly- increased peak flows, reduced lag time
Precipitation intensity influencing storm hydrographs
High Intensive rainfall= overland flow=steep rising limb& high peak flow
Low intensive rainfall= percolation= Increased lag time and reduced peak flow
Porosity and permeability of rocks influence on hydrograph
Impermeable surfaces clay cause water to pass overland resulting in high peak flows and a flashy response.
Permeable surfaces such as chalk and gravel reduce peak flow and increase time lag.
Slopes influence on hydrograph
steep- overland flow, shorter time lag, high peak flow
Shape of Drainage basin influence on hydrograph
Circular basins- respond quickly
linear basins- response is drawn out
Storm Hydrograph
Show how river discharge responds after a rainfall event, depicting varriation across 1-7 days.
Components of Storm Hydrographs
Approach segment -the period of time before
water from the rainfall event gets into the river
channel.
Quickflow- water that reaches the river quickly as overland flow or throughflow causing a rapid rise in the discharge level of the river.
Rising Limb- the speed at which the flood water begins to rise
Peak Flow- maximum discharge of a river during a storm
Time lag- Time between height of storm and peak flow
Recessional limb- speed with which water levels in the river decline after the peak
Bankfull Discharge- when the discharge of the
river is at the top of the river banks - any further
added discharge will cause the river to flood the
surrounding land and flow over its floodplain.
