Water extraction for industrial or domestic use reduces the amount of discharge in the drainage basin. For example, weeks of heavy rain may have fallen in a drainage basin with sandy soils and gentle slopes following a particularly dry summer when the water table fell significantly.
In this case, the ground may not reach saturation capacity for many weeks and an intense storm will not produce torrents of overland flow and flooding. Similarly, drainage basins tend not to be characterised by only one type of soil and rock or the presence or absence of an urban area and so will experience differences in infiltration rates and drainage density throughout the area.
In central London, there is no doubt that human factors have the most significant influence over discharge, whereas in rural Wales it could be argued that physical factors play a more central role. Urban areas comprise a lot of green spaces parks, gardens, grass verges , making the drainage pattern of basins extremely complex. It is inevitably going to be a combination of physical and human factors which control how much discharge is in a drainage basin. This is a must-read article from the BBC, suggesting our image of the UK as a concrete jungle may not quite be reality!
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Share: Facebook Twitter Email Print page. Physical characteristics Basin size This influences the lag time — a large drainage basin will mean that water takes a long time to travel through tributaries or the ground to reach the channel.
Basin shape Circular drainage basins mean that all points on the watershed are equidistant from the channel and this will lead to a shorter lag time and higher peak discharge. Elevation and slope A steeply-sided river valley means that gravity assists water in its descent towards the river channel, whereas gently sloping valleys tends to produce longer lag times and lower peak discharges. Rock type This has a profound influence on the rate of drainage in a basin.
Permeable rock assists percolation: Porous rock sandstone, chalk allows water to percolate through the pore spaces Pervious rock limestone allows water to travel along joints and bedding planes within the rock Both types of rock are characterised by a lack of surface drainage and have high rates of infiltration.
Soil type Soil type controls the rate of infiltration, soil moisture storage and rate of throughflow. The ground will get waterlogged by the heavy rain.
A pool is usually found on a meander whereas the riffle is normally seen on the straighter areas of the channel, they tend to be situated very close to one another, forming in sequences.
The aim of this investigation is to carry out a field investigation at a pool and riffle and compare the characteristics at these two sites with the objective to state the differences. For example, farming techniques which use earth-moving machines can appear effective for crop production, but will eventually damage the topsoil which thereby decreases crop productivity McLaren, Erosion is a substantial contributor to deterioration of soil quality.
Flood and furrow irrigation use a high influx of water to immerse the crop area. This will result to the process of runoff. Runoff is the surface flow from the areas of high elevation to the lower elevation. Plaster stated that the process of runoff happens when the rainfall or snowmelt cannot be absorbed by the soil and runs into the streams or lake.
Runoff may come from rainfall and melted snow or ice. The runoff process is very important in the water cycle because it helps the water to travel at different parts and also may changes the phase from liquid to gas or solid.
Open Document. Essay Sample Check Writing Quality. Drainage Density and Stream Order in a Drainage Basin Drainage Density represents an approach to the quantitative analysis of drainage basin. It is the average length of channel per unit area of the drainage basin. It is calculated as shown below. Drainage density is a qualitative analysis of the areal properties of a river basin. Drainage density is useful as a measure of frequency and spacing of streams within the drainage basin.
It also helps to determine the texture of dissection of a drainage basin- the extent to which the landscape is cut into by river valleys and in turn influence slope development. Generally, there are 4 categories of drainage density and corresponding texture of dissection. This will inhibit channel development and thus the reduction of drainage density. Identification of the link in The below shows the contrast between storm hydrographs of an area before and after urbanizations.
A flashier storm hydrograph will make the area more prone to flooding. Chinese experts believe that local deforestation, uncontrolled building and lack of flood control have led to massive floods that threaten loves and homes of millions. It indicates the closeness of spacing of channels, providing a quantitative measure of the average length of stream channel for the basin. High drainage density is the result of weak or impermeable subsurface material, sparse vegetation and high relief.
High drainage density gives rise to a fine drainage texture, while low drainage density results in a coarse texture Strahler , Closer investigations of the processes responsible for drainage density variation have revealed that a number of factors viz. According to Nag , low drainage density is generally characteristic of areas of highly resistant or permeable subsoil material, dense vegetation and low relief.
Drainage density of a basin also affects its hydrologic response to rainfall events, and thus the shape of its stream's hydrograph during a rain storm. Langbein recognized the significance of D d as a factor determining the time of travel by water to the outlet of a basin. Basins with high drainage density often have a relatively rapid hydrologic response and a hydrograph with a steep recession or falling limb, while a low drainage density means a slow hydrologic response.
High drainage densities indicate a greater flood risk. Thus the measurement of drainage density provides the hydrologist or geomorphologist with a useful numerical measure of landscape dissection and runoff potential.
Drainage density varies inversely as the length of overland flow, and thus to the rate of infiltration. In other words, a river basin in which the floor consists of permeable rocks tends to have fewer streams per unit area than one floored with impermeable rocks. In hilly terrain, drainage is controlled by faults, fractures, thrusts and other lineaments within a basin.
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