2 - catchment hydrology, the drainage basis as a system ✅ Flashcards
what is a drainage basin
drainage basin is an OPEN SYSTEM meaning it has inputs and outputs
what factors affect a drainage basin’s output (8)
- level of interception
- type, amount, duration, intensity of precipitation
- relief
- rock type
- soil type
- drainage density
- other use of the river
- land use
what are the runoff processes in hillslope hydrology
- horton overland flow
- subsurface stormflow
- return flow
- groundwater flow
what factors affect water movement in soils (infiltration)
FLOW INFLUENCES (flow head, viscosity, flow chemistry, soil chemistry, soil and water temp, air entrapment)
SOIL SURFACE CONDITIONS (land use, vegetation cover, roughness, cracking and crusting, surface sealing)
INFLUENCING FACTORS (mechanical processes, frost, residue/organic matter, compaction, antecedent soil water, chemical/biological/microbial activity)
SUBSURFACE CONDITIONS (soil (hydrologic group, texture, porosity, depth, shrink and swell, layering, spatial variability, structure) , root system, water table depth, subsurface drainage, water release relationship, hydraulic conductivity)
HYDROPHOBICITY (dryness, heat, plant chemicals, aromatic oils, other chemicals)
explain horton overland flow
- occurs when rainfall intensity exceeds infiltration capacity and then:
water fills surface depression, water spills over downslope as overland flows eventually to stream - once thought to be only mechanism of runoff generation
- became coded into hydrologic models still in use today
what is subsurface stormflow and what does it consist of
lateral flow through soil above conductivity contrast
consists of both slower matrix flow and faster macropore flow
explain saturation overland flow
direct rainfall onto saturated areas
return flow from saturated soils in topographic lows and along valley bottoms.
water table rises to intersect the surface.
rains for a sufficient duration that the subsurface becomes locally saturated from below.
what is the water balance of drainage basins
net difference between precipitation and evaporation yields streamflow or groundwater
what is the difference between losing and gaining stream
LOSING - in arid regions, streambeds dry, when storm flows fill channel, water infiltrates through bed recharging aquifer below
GAINING - in humid regions, streambeds wet and groundwater recharged by frequent rainfall. flows into stream maintaining baseflow
what are the flows that transfer precipitation in a drainage basin (6)
- throughfall and stemflow
- infiltration
- throughflow
- percolation
- groundwater flow
- overland flow
what are drainage basin outputs
- evaporation
- transpiration
- channel discharge (cumecs)
what is a drainage basin
watershed and catchment area
area of land drawing precipitation into particular river/river system
WATERSHED marks boundary between one drainage and another, characterised by topography
CATCHMENT AREA - area of land within drainage basin itself
what are different types of flows
CHANNEL FLOW - river flowing through river channel at speed dependent on efficiency
OVERLAND FLOW (surface runoff) - water travels across surface of ground when it cant infiltrate (when ground is baked, saturated, frozen) impermeable rocks are common
INTERFLOW - water can travel above water table through permeable rocks
BASEFLOW - if groundwater flow (travelling beneath water table) feeds into a river
factors affecting evaporation
- temperature (warmer = more evap.)
- water available (less water = less evap.)
- humidity (higher = slower evap)
- wind speed (more wind = more evap)
- colour of surface ALBEDO (lighter colours reflect heat away = less evap)
what characteristics of rainfall affect local hydrology
- total amount of precipitation (more = more infiltration+percolation, water table raised, saturated ground = more surface runoff but less rainfall = vegetation will intercept less rainfall and may die)
- intensity of rainfall (heavy = quickly saturated ground, increased runoff/channel flow, flooding)
- type (snow, rain etc) (infiltration easiest with rain, snow takes ages to melt, vegetation intercept rain quicker)
- geographic distribution (if falls directly into river channel will affect levels quicker)
- variability (how much the amount of rainfall varies over time, periods with less than normal = drying up river channel)
