Hydrology
Drainage system notes:
- Amount of interception dependent on leaf size, time of
year, deciduous vs coniferous.
- Soil moisture increases with addition of organic matter
(leaf drop).
- Overland flow can occur on ground baked hard by a
drought, on steep ground, on frozen ground, on tarmac,
in areas of impermeable rock (e.g. granite), and where
ppt intensity > infiltration capacity (Hortonian OLF).
- Infiltration capacity is influenced by duration of rainfall,
antecedent soil moisture, soil porosity, vegetation
cover, raindrop size, and slope angle.
- Percolation is the subsequent downwards movement of
water through the soil to the bedrock after infiltration.
- Groundwater flow is beneath water table.
- Baseflow is year-round, slow flow of water that explains
why major rivers don’t dry up during long hot summers.
- Beneath the water table all pore spaces are full
(saturation).
- Recharge involves rising of the water table after a dry
spell (refilling of water in pores).
- Springs occur on saturated ground and involve
exfiltration.
, How storm hydrographs are affected by drainage basin
size/shape:
- LARGE drainage basin = higher discharge, but longer lag
time.
- LONG and THIN drainage basin = delayed response.
- CIRCULAR drainage basin = more rapid response.
- STEEP RELIEF = FLASHY response and higher peak
discharge as no/limited time for rainwater to infiltrate,
so rapid SRO likely.
- HIGH RAINFALL INTENSITY = FLASHY response as
precipitation intensity is greater than infiltration
capacity, so not all rain can be infiltrated, leading to
Hortonian OLF.
- WET PREVIOUS CONDITIONS = FLASHY response as pore
spaces full and ground is saturated, so no infiltration and
all SRO.
- HIGHLY URBANISED catchment = FLASHY response as
tarmac etc. is impermeable (leading to SRO) and storm
drains transfer water rapidly to rivers (high drainage
density).
- PPT IN FORM OF SNOW = DELAYED, then SUDDEN
response (water held in storage as snow, then melting
causes sudden SRO). Can cause flooding.
Drainage system notes:
- Amount of interception dependent on leaf size, time of
year, deciduous vs coniferous.
- Soil moisture increases with addition of organic matter
(leaf drop).
- Overland flow can occur on ground baked hard by a
drought, on steep ground, on frozen ground, on tarmac,
in areas of impermeable rock (e.g. granite), and where
ppt intensity > infiltration capacity (Hortonian OLF).
- Infiltration capacity is influenced by duration of rainfall,
antecedent soil moisture, soil porosity, vegetation
cover, raindrop size, and slope angle.
- Percolation is the subsequent downwards movement of
water through the soil to the bedrock after infiltration.
- Groundwater flow is beneath water table.
- Baseflow is year-round, slow flow of water that explains
why major rivers don’t dry up during long hot summers.
- Beneath the water table all pore spaces are full
(saturation).
- Recharge involves rising of the water table after a dry
spell (refilling of water in pores).
- Springs occur on saturated ground and involve
exfiltration.
, How storm hydrographs are affected by drainage basin
size/shape:
- LARGE drainage basin = higher discharge, but longer lag
time.
- LONG and THIN drainage basin = delayed response.
- CIRCULAR drainage basin = more rapid response.
- STEEP RELIEF = FLASHY response and higher peak
discharge as no/limited time for rainwater to infiltrate,
so rapid SRO likely.
- HIGH RAINFALL INTENSITY = FLASHY response as
precipitation intensity is greater than infiltration
capacity, so not all rain can be infiltrated, leading to
Hortonian OLF.
- WET PREVIOUS CONDITIONS = FLASHY response as pore
spaces full and ground is saturated, so no infiltration and
all SRO.
- HIGHLY URBANISED catchment = FLASHY response as
tarmac etc. is impermeable (leading to SRO) and storm
drains transfer water rapidly to rivers (high drainage
density).
- PPT IN FORM OF SNOW = DELAYED, then SUDDEN
response (water held in storage as snow, then melting
causes sudden SRO). Can cause flooding.
