Hydrology and fluvial morphology

• How is a floodplain formed?

  - River exceeds its maximum volume and bursts its banks

  - The water is shallower over the floodplain and has a higher hydraulic radius meaning greater friction and a decrease in velocity, leading to deposition

  - finer lighter material is deposited furthest away from the main river channel.

  - It is very fertile
• What is a River Bluff?

  - The bluff line is a slope, marking the outer edge of a floodplain

  - River bluffs are erosional features marking the limits of the floodplain as the river meanders back and forth
• What is field capacity?

  the maximum amount of water a soil before oversaturation
• What is antecedent moisture?

  Pre-existing level of moisture within the soil before precipitation
• What factors effect the shape of a storm hydro-graph?

  - Vegetation

  - Soil type

  - Rainfall intensity

  - Urbanisation

  - Relief

  - Antecedent moisture

  - Basin shape and size
• What are the four types of erosion?

  - Hydraulic action

  - Abrasion (When pebbles grind along the river bank and bed in a sand-papering effect.)

  - Attrition

  - Solution
• What are the four types of transportation?

  - Traction

  - Saltation

  - Suspension

  - Solution
• What is cavitation?

  - Air bubbles generated by increased turbulence in moving water.

  - These air bubbles expand the fracture lines within the bed and the banks.
• Example of a porous soil?

  Sandy soil
• Example of a non-porous soil?

  Clay soil
• What is calibre?

  The size of a particular pebble or particle in a river at a given point
• What is a river's capacity?

  The total capacity sediment load of a river at a particular point
• What is competence?

  The size of the largest sediment particle that can be carried by that river.
• How is a Leeve formed?

  - During a flood event where a river's bank bursts as it has exceeded its maximum volume

  - Sediment is carried in suspension

  - When the flood loses velocity (energy), the thickest and coarsest sediment is deposited at the channel edge as finer sediment is transported further to the floodplain

  - Overtime, this will result in heightened river banks
• How is a braided channel formed?

  - A braided channel occurs when there is a dense sediment load being carried in the river and not enough energy to entrain it

  - A sudden drop in discharge levels results in a mid-channel bar which is above water and increases downstream as the stationary sediment is now exposed.

  - The upstream end becomes stabilised with vegetation.

  - The established bars (Eyots) become effect narrows the channel

  - The channel bar results cause the water flow to split and flow on the two smaller cross sections on either side
• What are the conditions needed for a braided channel?

  - high load in a river

  - a river's gradient

  - fluctuating discharge

  - found in the lower profile as there is lower energy for transportation to occur.
• What are pools?

  Deeper area's of a river channel where erosion is dominant
• What are riffles?

  Shallower area's of a river channel where deposition is dominant
• How is Helicoidal flow created?

  - High sediment channels will form a sequence of pools and riffles that accentuate vertical turbulence

  - This combined with horizontal turbulence and the thalway, the water will begin to take up a spiralling motion

  - The water will spiral from the outer bend, where it erodes, down to the river bed, then to the inner bend where it deposits any material it carried from the outer bend.
• How is turbulent flow created?

  - Channel bed roughness from high sediment loads leads to lots of friction with the river bed.

  - Water at the center of the channel overtakes water at the side of the channel, leading to a chaotic flow

  - Water at the sides eddy towards the banks and water closer to the bed eddy's downwards

  - Cavitation and potholes are common
• What is laminar flow?

  - A smooth gentle flow

  - Water flows in layers parallel to the bed with little mixing between them

  - Only possible on man-made surfaces.
• How is a meander formed?

  - A sequence of pools and riffles leads to a swinging motion of the thalweg leading to helicodial flow

  -velocity is the fastest on the outer bend at pools, erosion is dominant. This leds to a river cliff

  - Any eroded material at the outer bend will be transported to the inner bend through the Thalweg where it is deposited. helicoidal. This creates a slip-off slope

  - Meanders will migrate overtime as the horse-shoe shape is accentuated until it reaches a river bluff
• How is a spring formed?

  - pressure forces water from an underground aquifer to the surface. - the water table reaches saturation and field capacity

  - As a result, water from the aquifer appears at the earth's surface, forming a spring
• How are interlocking spurs formed?


  - in the upper course of a river most of the erosion is vertically downwards. this creates steep-sided, V-shaped valleys.

  - the rivers aren't powerful enough to erode laterally

  -they have to wind around the high hillsides that stick out their paths on either side. the hillsides that interlock with each other as the river winds around them are called interlocking spurs
• How rapids form?

  - When there is a sudden increase in gradient without a break in slope

  -This can occur as in the upper course there are different bands of hard and soft rock, which erode at different rates, leading to an uneven river bed

  -Water had to flow over these changing gradients. -This creates an uneven flow on the channel surface
• How is an oxbow lake formed?

  - River channels want to take the path of least resistance

  - Increasing curvature leads to decreased width of neck - River cuts through at times of high discharge, meaning water is not traveling through the horseshoe bend shape but instead straight across

  - Deposition occurs in the cut-off and overtime is consolidated by vegetation growth