Notes and Revision for Geography:
Links: https://sites.google.com/a/halliford.net/a-level-geography/home/exam-materials http://coolgeography.co.uk/A-level/AQA/AQA%20A%20level.htm http://web.aqa.org.uk/qual/gce/humanities/geography_materials.php
Topic 1: Rivers and Flood Management.
A drainage basin is an area drained by its rivers and tributaries. It is a natural system with varied inputs of precipitation and varied outputs of water, for example, inputs: rain, snow or ice, outputs: evaporation, transpiration, and evapotranspiration and river flow. When the inputs and the outputs balance out it is called the water balance. The summary of water balance: Precipitation= evaporation + transpiration + river flow + storage NOTE: water is stored in porous rocks, soils, peat and vegetation. During heavy rainfall or a monsoon the water or “precipitation” storage is high. However when there is little rain or a drought then the precipitation storage is depleted. River Discharge:
The river discharge is the volume of water that flows in a river channel (usually per second) A few examples of FACTORS affecting and influencing river discharge: Geology: permeable rocks like chalk would store most of the precipitation and then release it slowly. This reduces the discharge. However impermeable rocks have the opposite effects. Slopes: water tends to move slower through or across gentler slopes than it does on sheer or steeper slopes. If the slope is steep it is usually located upstream, also with steep slopes rapid water movement occurs which causes white water. With gentler slopes that are usually located downstream, water flows gently, hence the name. Soils: same effects as permeable rocks but once the soil storage becomes too high the water will not be absorbed. Impermeable soils like clay soils do not absorb water at all and in turn increase discharge. Drainage density: the length of a channel in kilometres squared. With high drainage density there is a decrease in the time taken for surface and subsurface water to be transferred to river channels. Vegetation/ interception: if there is masses of ground or above ground vegetation precipitation will, either way, be decreased. The vegetation above ground intercepts the precipitation falling from the sky. The few drops that make it through either gets absorbed by the trees or are intercepted again by ground level vegetation like bushes or large plants. Vegetative interception is a key factor AFFECTING the river discharge. Land use: manmade drainage can intercept the rainfall. If rain has to flow through a town to reach a river it is highly likely that some or most of it will fall down a drain. However the drain will likely reach the river eventually but over a great period of time. The process of water evaporation and the cycle of how it returns to the river it evaporated from is called the hydrological cycle
The storm hydrograph records the fluctuation in rainfall over a certain length of time.
Here is a labelled storm hydro graph. I will go through the labels and their meanings. Rising limb: “the increase in discharge in response to precipitation” the steeper the rising limb, the faster the water made it to the river. Precipitation: usually in millimetres, the amount of rain that fell over the time that has been recorded. The long profile:
The long profile is the length from the source to the mouth of a river. Most rivers are concave in long profile; this is known as a graded profile, with a relatively short (but steep) section near the source (usually upstream) and a longer section with gentle gradients near the mouth (usually downstream). In the long profile of a river many processes happen to help either form the river, landscape it or transporting and eroding sediment.
An example of a long profile in 2D...