Storm hydrograph Flashcards
Base flow on storm hydrograph is…
the regular flow of a river, when there is no rainfall.
Smaller drainage basin:(compared to larger)
-shorter lag time
-higher peak
Water reaches the channel more rapidly as water has a shorter distance to travel.
More circular drainage basin:(compared to more elongated)
-shorter lag time
-higher peak discharge
It takes less time for the precipitation to reach the channel.
Circular drainage basin means…
that all points on the watershed are equidistant from the channel, so it takes less time for water to reach the channel.
Steeper basin:(Relief)
-shorter lag time
-higher peak
Water reaches the channel faster as it travels more quickly downhill.
Type of precipitation:
The lag time and peak are lower after a snowfall, as the water is stored on the ground surface.
If the snow melts…
the water will reach the channel quickly as infiltration is impeded if the ground is frozen.
Intense rainfall causes…
excess-overland flow.
Prolonged rainfall causes…
saturated overland flow.
Impermeable rock is…
saturated more quickly than porous rock. Saturated overland flow is common.
Vegetation intercepts a large…
proportion of rainfall. In forested drainage basin, the lag time and peak are lower.
In areas of sandy soil…
the lag time and peak are lower. Sandy soil has larger pores than clay soil. Infiltration is more rapid.
In urban areas, there is higher…
surface run-off as there are more impermeable surfaces and sewers take water rapidly to rivers.
In a deforested basin, there is less…
interception, evapotranspiration and surface-runoff.
Water quality decreases due to deforestation as…
more eroded topsoil enters the channel(may contain fertilisers)
Increased nitrate levels encourage…
aquatic plant growth, resulting in eutrophication(choking) of the river.
Cattle bred in a deforested area…
remove remaining vegetation and increase the surface runoff.
Deforestation increases the light…
intensity, wind speed. The area becomes drier and maybe desertified.
Irrigation can decrease…
the water table.
Large expanses of irrigated land may increase…
evapotranspiration rates, thus increasing precipitation and in some cases tornado frequencies.
Interception loss is…
part of rain retained by an aerial portion of vegetation(canopy)
As the agricultural crop density increases…
the interception loss as well, especially from cereal crops.
Coniferous(evergreen) trees intercept more…
than deciduous trees in the winter, but less in the summer.
Coniferous trees have relatively high…
surface area. Pine needles allow for water to accumulate.
After a certain amount of water on the leaf…
the leaf bends down and water drops.
Different trees have different…
interception loss. E.g. spruce has higher annual interception compared to the beech.
The 3 Ps
- porosity
- permeability
- perviousness
Porosity is…
a measure of the distance between rock particles. (the size of the pores).
Permeability is…
a measure of the ability to transmit water through porous rock.
Perviousness is…
something which allows water to pass through it due to cracks or defects in the rock.
Antecedent soil moisture is…
the pre-existing levels of moisture, before rainfall.
River regime is…
annual variation in the discharge of a river.
