Describe and explain the formation of channel features that can be created by the process of river rejuvenation (15 marks) The long profile of a river is not a static entity and is prone to change due to changes in sea level. Over very long periods of time large changes in sea level can drastically alter the rivers potential energy and can increase the chances of vertical erosion. Sea levels change because of two principal causes - isostatic changes and eustatic changes, both of these changes can lead to rises or falls in sea level. Isostatic changes are local changes where the height of the land changes relative to the global sea level. An example of this can be found in glaciation.
Land use and other human activities also influence the peak discharge of floods by modifying how rainfall and snowmelt are stored on and run off the land surface into streams. With less storage capacity for water in urban basins and more rapid runoff, urban streams rise more quickly during
Causes of the Flood The flood was a result of many exceptional factors, including both physical and human. One major factor is the topography of the land. Boscastle is within the Valency valley. The river follows a very steep course into the valley itself from surrounding hills. Boscastle stands on the confluence of the River Jordan and the River Valency so there was an exceptional amount of water passing through the village.
Describe how, and explain why, channel characteristics change downstream. (15 marks) Channel characteristics are changed when the river flows downstream by many factors such as cross-profile of a river, wetted perimeter, erosion, hydraulic radius, roughness and efficiency. Channel characteristics change as the river flows from upstream to downstream. In the upper course the river tends to be more narrower, steep and uneven due to the deposition of large boulders it also has a larger wetted perimeter. The bank of the river channel becomes worn away as a result of vertical erosion, due to the processes of hydraulic action which is the forces of flowing water against the river bed and banks caused by the volume of flowing water compared to kinetic energy and attrition which is the material being carried in the river colliding which then breaks the loads down into smaller pieces.
These long term variations in sea level can be caused by major glacial episodes, changes in the hydrological cycle, vertical land motion or even changes in the ocean and coastal circulation. These reasons can be put into two categories which are known as eustatic and isostatic change. Over the years the global sea level has overall significantly increased from 16BC which was when it was the world’s lowest sea level, however, it has fluctuated throughout the past thousand years. Eustatic change is when there is a rise or fall in sea level changes relative to the land, due to an alteration in the volume of water in the oceans or, alternatively, a change in the shape of a drainage basin and hence a change in the amount of water the sea can hold. Throughout and after an ice age, eustatic change takes place.
This isolation may be due to human practices or natural occurrences which drive aggradation or in‐stream incision. When high flows occur under these physical conditions, the stream or river has a restricted area to flow and higher flow velocities and energies are produced. Ideally, during high flows the river system would be able to over top its banks and spread over a large flat area surrounding the river, the floodplain (Figure 1). Floodplain reconnection reestablishes the connection between the stream system and its floodplain. This is accomplished through lowering or setting back natural or constructed levees currently blocking the flow of water out of the main channel.
Much controversy came about due to the construction of the Glen Canyon Dam as part of the Colorado River Compact, which aimed to 'ensure through water storage the delivery of sufficient water to the lower basin during years of drought, so as to allow the upper basin to better utilize its allocation of river flow' as proposed by The USBR (United States Bureau of Reclamation). The construction of the dam led to the creation of Lake Powell, a reservoir which brought in its own revenue through tourism and recreational activities such as jet-skiing. The Glen Canyon Dam is also major generator of the Colorado River Storage Project, comprising 75-85% of total CRSP generation. However, environmentalists such as the Sierra Club (a large-scale environmental
Raising Scoggins Dam would affect tributaries to Hagg Lake as well as Scoggins Creek downstream of Scoggins Dam. Therefore, the Project Area includes areas potentially inundated by the increased size of Hagg Lake as well as Scoggins Creek downstream of Scoggins Dam. Anadromous salmon and trout as well as resident fish species and Species of Special Concern (state or federal) occur within the Project Area. Methods Sources of existing fisheries information and data included the Oregon Rivers Information System (ORIS); StreamNet; Oregon Natural Heritage Program; Oregon Department of Fish and Wildlife (ODFW) project area files, reports, and data; Clean Water Services (CWS);
All these elements are highly influenced by the below stated conditions. The main structure of a drainage basin, one of the bullets factors, which can affect the shape of storm hydrograph. It is separated in three different factors, size, shape and relief. The size of a drainage basin determines the distance the water has to cover from the precipitation falling point and the hydrograph flow station. Naturally, the lager the drainage basin the longer the way the water needs to cover the longer the taken time to reach the measuring location.