Rivers

• A drainage basin is an area of land that feeds a river, all the precipitation that falls in this area will flow into the river.
• The source of a river is where the river begins, the source is often a spring (a natural flow of water from the ground) in an upland area.
• The mouth of a river is where a river meets the sea, the widest part of a river.
• Our key river case study is the River Tees
• The River Tees is 137 km long.
• The long profile of a river is a way of displaying the channel slope of a river throughout its entire course,
• The cross profile of a river shows how the width and depth of the river valley and channel change as you move downstream.
• The River Tees starts in the moor lands.
• The Bradshaw Model shows how a river changes from upstream to downstream.
• There is greater friction in the upper course of the river as it has a greater amount of water touching the edge, meaning the mean velocity is higher downstream.
• Load is the material carried by a river, the shape and size of the load changes as you move downstream.
• Upper course --> Erosion

  Middle course --> Transportation

  Lower course --> Deposition
• Interlocking spurs are found when the river cuts vertically into the valley, creating steep sides. The river winds around areas of more resistant rock. Interlocking spurs are steeper on one side, where the river cuts into it. They are only found in upland areas.
• Waterfalls are formed towards the upper course of a river, the soft rock is undercut by erosional processes, forming a plunge pool. Overtime the soft rock continues to erode, creating an overhang of hard rock. The overhang eventually collapses, leaving more rocks for abrasion. Overtime as the waterfall continues to retreat, a gorge will form.
• Load can be transported through solution, suspension, saltation and traction.
• Saltation is where smaller stones are picked up and dropped again which results in a skipping motion.
• Traction is where larger stones are dragged along by being rolled, this only happens when the river is really high flow.
• Solution is where dissolved chemicals are carried along in solution invisible to the naked eye.
• Suspension is where tiny particles are carried in the river's currents and make the river appear brown and muddy.
• A meander is a series of curves, bends and loops within a river.
• Meanders are formed in the middle or lower course of a river, as the slope is less steep and allows for the river to erode at the sides of its channel. The water flows the fastest on the outside of the bends, so this is where most of the erosion takes place, water flows slower on the inside of the bend, so this is where the material is carried to. The sediments are then deposited to from a gentle bank on the inner curves, eventually the bend of the river becomes greater until the ends are very close together and sometimes the neck of the meander is broken to form an oxbow lake.
• A flood plain is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls. It experiences flooding during times of high discharge.
• The flood plains of the River Tees are Middlesborough and Stockton on Tees.
• An estuary is the tidal mouth of a large river, estuaries form a transition zone between river environments and maritime environments.
• The River Tees has a large estuary.
• Levees are formed naturally due to floods, where the thickest, coarsest sediments are deposited at channel edges and the thin, fine sediments are deposited on the outer parts of the flood plains. After many floods natural levees are built up from the deposition of sediments.
• Permeable means a material that allows water to flow through it. Permeable rock has pores in it that allow water to soak through.
• Saturated means holding as much water or moisturise as can be absorbed. Permeable materials can become saturated.
• A hydrograph tells us whether or not a river is likely to flood by showing the rainfall and discharge.
• On a hydrograph, the pink bars show rainfall, and the green line shows discharge.
• The base flow on a hydrograph is the average level of discharge for the river.
• The lag time on a hydrograph is the time between peak rainfall and peak discharge.
• Impermeable rock decreases lag time as it increases surface run off, because rain cannot infiltrate it. It increases flood risk.
• Steep slopes decrease lag time, and increase surface run off as the rain slides of the slope, increasing flood risk.
• Long, narrow drainage basins increase lag time, making more space between connecting rivers, making it less likely to flood (decreasing flood risk)
• Long periods of rainfall (antecedent conditions) decrease the lag time, as heavy long periods of rainfall saturate the soil reducing infiltration. Increasing flood risk.
• Urbanisation decreases lag time, as road surfaces are impermeable, causing surface run off to increase, as well as the flood risk.
• Deforestation decreases lag time, reduces interception and infiltration, whilst increasing surface runoff, and increasing flood risk.
• Our key flood case study is the Sheffield flood, June and July 2007.
• The Sheffield Flooding 2007 was influences by several factors:

  • it has five rivers joining at confluences in the city.
  • poor river management limited the ability for the river to naturally overflow
  • Sheffield is heavily urbanised and much of it is made of impermeable surfaces
  • some flood defences were not strong enough and were breached.