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36 Cards in this Set
- Front
- Back
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what is the drainage basin? |
an area of land drained by a river and its tributaries. |
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what is the drainage basins boundary marked by? |
a ridge of high ground- water shead beyond which any precipitation will drain into the next adjacent basin |
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define the following: runoff , overland flow, subsurface flow, groundwater, hydrograph |
Runoff: amount of water flowing in a channel at the point of measurement. overland flow: water flow over the surface of Ground water: water in saturated layer of rock hydrograph: rise and fall in amount of runoff in response to a storm. |
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what are the two main types of runoff? |
Hortonian overland flow saturated overland flow. |
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what is Hortonian overland flow? |
a pond that forms on the surface because the rain fall arrives at the ground surface at a rate higher then it can be soaked up. once the depressions are filled then water will flow downhill. this causes an overland flow. |
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what are the required conditions for the Hortonian overland flow? |
high intensity rainfall, and low infiltration capacity surface. |
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what is saturated overland flow? |
response of streamflow to storms in humid area. much of the flow to streams were subsurface. surface flow occured after pro longed rainfalls as areas of hillslope become saturated as soil stores become full. Areasof saturation expand as rainfall continues = partial contributing areas. which contribute directly to overland flow. |
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where does saturated overland flow occur first? |
base of the slopes |
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how was it investicated? |
through flow pits as measurments of flow along the soil horizons |
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what are the characteristics of saturated flow? |
delayed response to rainfall, occurs in humid areas with dense vegetation and deep soils. |
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what factors contribute to run off? |
through flow by push through effect, rapid subsurface flow through pipes water percolates vertically to ground water groundwater is a major component of base flow. especially in permeable rock areas. |
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what factors influence run off? |
precipitation vegetation cover regolith lithology - permiability and water table height topography- slope gradient catchment area shape. |
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what is discharge? |
the amount of water flow |
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how is the channel slope kept stable in a gauging station |
installs gauging structure in the channel. |
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what is laminar flow? |
water particles move along paths- dont disrup the movement of neighbouring particles. most resistance- caused by intermolecular viscous forces resistance = alfa to velocity |
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what is turbulent flow? |
water moves in all directions and velocity fluctuates. most resistance is generated along the channel perimeter. related to channel slope particle size and concentration resistance is alfa square of velocity. |
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how do layers move in laminar flow? |
smoothly past each other. |
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how do layers move in turbulent flow? |
exchange between layers, eddies. |
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how can you distinguish between turbulent and laminar flow? |
Reynolds number measures all fluid flow including air |
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what two ways can flow be classified in? |
tranquil (streaming) rapid (shooting flow) |
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when is flow tranquil? |
when obstacles have a damming effect and disturbances are transmitted upstream. |
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when does rapid flow occur? |
motion is not affected by an obstacle. |
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what happens where flow changes from tranquil to rapid? |
water level falls evenly but the transition of rapid to tranquil is usually abrupt and marked by a turbulant surface roller/hydraulic jump |
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how are tranquil and rapid flow distinguished ? |
by fraud number when F<1 tranquil flow when f>1 it is rapid |
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what are bed forms relative to? |
fraude number. |
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what does channel morphology have a large effect on? |
velocity. |
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how are roughness and friction effects integrated? |
by mannings n roughness factor or chezys factor. |
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what are the components of roughness and friction? |
sinuosity of the channel nature of bed and banks- concrete or vegetation extent of obstacles the higher the roughness the greater the frictional effect reducing velocity. |
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when does fluid carry suspended particles? |
when it is flowing |
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what is the settling velocity? |
the minimum velocity a flow must have in order to transport rather than deposit sediments |
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what is the settling velocity given in? |
stokes law. |
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what is entrainment? |
the initial settling into motion of a grain in a fluid |
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explain how entrainment works?? |
particles on the channel bed are subjected to drag due to the increase in fluid pressure on the up stream side. if forces on the grain over come resistance to movement, then the grain rises from the bed. |
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how does channel morphology influence the distribution of erosion and deposition? |
because the size of the sediment moved it related to velocity, the velocity is related to the size of the channel and the gradient and inversely to roughness. |
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what do velocity and sediment size alter? |
the morphology |
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why do relations between process and form tend to occur (ie width and discharge) |
because the adjustment of form to input of water and sediment mean there is a constant relationship. |
