Rivers

•Circular depression on the river bed carved out of solid rock. •Formed by a drilling action as pebbles are caught in eddy currents and whisked around within a small natural crack or hollow. •As time passes, the drilling action enlarges the hollow to form a pothole. •Commonly found below waterfalls or rapids, where hydraulic action is a significant process.

•Small series of waterfalls associated with very disturbed turbulent water. •Forms when rocks or varying resistances cut across a valley and erosive process create a series of steps.

•Found where there is a sudden increase in the slope of the slope of the channel or where the river flows over a series of gently dipping harder bands of rock •As the water becomes more turbulent its erosive power increases.

•Sudden step in a river’s long profile. •Often the result of a tougher, more resistant band of rock cutting across the valley. •Unable to erode the rock at the same rate as neighbouring rocks, a step is formed and a waterfall results. •Over time, the river cuts backwards into the resistant rock causing the waterfall to retreat backwards. Forming a narrow, steep sided gorge.

•A narrow valley between hills or mountains. Typically with steep rocky walls and a steam running through it. •Waterfalls are not uncommon.

•When a river subdivides into smaller streams •In between these channels, small islands of deposited sediment will form. •Braiding occurs when there is a sudden decrease in energy causing deposition of large amounts making the channel subdivide.

•Natural embankments of sediment formed when the river floods and deposits it.

•Flat area of land bordering a river that is subjected to periodic flooding. •It’s made up of silts and sands which have been deposited over many years. •As a river floods its velocity is dramatically decreased, causing energy to be reduced and a bulk of sediment left floating in a thin sheet of water on the flood plain. •Once the water evaporated, a fresh layer of alluvium will be left behind, this is what makes a flood plain so fertile and good for farming upon.

•Formed when a river enters a sea or lake losing velocity, energy, capacity and competency causing a large amount of sediment to be deposited as a delta. •Rivers flowing over deltas tend to break up into many smaller channels called distributaries. •Two types of delta are Arcuate (Fan shaped) and bird food (Shaped like a bird’s foot).

•Remnants of the former floodplain prior to rejuvenation. •Terraces create steps in the valley cross profile.

•A meander that lies at the bottom of a steep walled canyon •Most often occurs at an existing meander after the rejuvenation of a river. •There is then severe downwards erosion creating a steep walled canyon. •Two types of incised meander: •Entrenched: have a symmetrical cross section resulting from very rapid incision by the river of the valley sides being made of hard, resistant rock. •Ingrown: formed when the incision or uplift is less rapid and the river may shift laterally, producing an asymmetrical cross section shape.

•Reforestation •Forecasts and warnings •Land use zoning •River restoration schemes •Wetland and river bank conservation

•Flood embankments •Artificial raising or straightening of channels allowing a greater capacity for water. Also has the consequence of increasing the velocity of the water. May cause problems down stream. •Channel enlargement •This involved dredging and the removal of large boulders from the river bed. It increases channel efficiency and reduced roughness. River velocity increases. •Flood relief channels •Take excess water around a settlement. •Dams •Allows water to be stored temporarily in a reservoir the rate at which water passes through into the river can be controlled. •Removal of settlements