Cross section of a river

being new to the river; they have undergone minimal attrition in comparison to rocks in the middle and lower-course. These rocks cause friction lowering the discharge in the upper-course. Another factor in the discharge of the river is whether the rock is impermeable or permeable. In Holford Combe, although the rock below the river (red sandstone) was impermeable, it was fractured allowing infiltration. This fracturing was due to the same tectonic plate movement that formed the Alps. Another feature found in the upper-course of rivers are waterfalls. These are formed when water passes over hard rock, eroding softer rock below. This forms a plunge pool where water and bedload swirl around, eroding the river backwards through abrasion and hydraulic action. Eventually this backwards erosion undercuts the harder rock and the harder rock collapses under gravity forming a waterfall.In the middle course the velocity of the river was higher because the large, angular rocks that had previously caused friction, had undergone attrition making them smaller, rounder and less-obstructive. This higher velocity allows the water to begin laterally eroding the sides of the river with hydraulic action, eventually forming meanders. These meanders become more and more bent until a point where it is quicker for the river to just cut through the neck of the meander cutting It off from the river. This forms an ox-bow lake which eventually, when it is full off vegetation becomes merely a meander scar. The relief here isn’t as steep and the valley is no longer v-shaped. This is because the lateral erosion taking place undercuts the sides of the valleys and collapses them until the valley is much flatter and wider than before. Other features of the middle-course of a river include levy’s, where the river floods and deposits its sediment on either side of the river, and terraces, small raised platforms on the floodplain which are actually the result/s of previous floodplains. Neither of these features, however, could be found in Holford Combe. In the lower-course of the river, the rocks were extremely small and round, and all of the bedload was either in the form of saltation or solution. This was due to the massive amount of attrition they had undergone. The valley shape in the lower-course of the river was flatter and wider due to further erosion of the banks of the river. Because of the increase In discharge at this stage in the river, lateral erosion had also increased making the river channel smoother and wider. One feature of the lower-course of a river is a delta. Deltas are an area of fertile land at the mouth of a river. They are formed when a high-energy river carrying lots of sediment hits the sea, loses all of its energy and suddenly drops all the sediment it was carrying, forming a small area of land.