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FRESHWATER (DRAINAGE BASIN HYDROLOGY AND GEOMORPHOLOGY (River discharge…

- - - - Turbulent flow
        
        chaotic flow with eddies around obstacles with an overall downstream direction. Amount of turbulence depends on friction of bed and banks and velocity
      - Laminar flow
        
        no friction with bed and banks - rare in nature
    - - Wetted perimeter
        
        the distance of bed and banks of the river in contact with the water
      - Hydraulic radius
        
        Ratio between the length of the wetted perimeter and the cross-section area
      - Cross profile
        
        Meandering channel
        
        An asymmetrical channel carries faster-moving water towards the outside of a bend
        
        Straight channel
        
        Symmetrical channel
        
        Fastest flow in the centre slightly below the surface
      - Roughness
        
        Decrease as a river flows from the upper to lower course
        
        Pebbles, stones and boulders on bed and banks of the river increase the roughness of the channel
        
        Increased roughness increases the length of wetted perimeter relative to channel cross section. This increases friction and decreases the velocity of the river.
      - Efficiency
        
        Smaller cross-section area = better efficient
    - - Average velocity
        
        Downstream the river becomes more efficient with proportionally less contact with its bed and banks
        
        Shown by higher hydraulic radius and lower channel bed roughness
        
        Steady increase downstream
      - Load quantity
      - Channel depth
      - Load particle size
      - Occupied channel width
      - Channel bed roughness
        
        Decreases because of fewer stones, smaller load particle size
      - Discharge
      - Slope angle (gradient)
  - - - Solution
      - Suspension
      - Saltation
      - Traction
      - River capacity and competence
        
        Capacity
        
        total volume of load a river can carry
        
        Competence
        
        diameter of the largest particles a river can carry for a given velocity
        
        shown through Hjulstrom curve
    - - a decrease in the volume of water in the channel
      - an increase in the friction between water and channel
      - a shallowing of gradient which decreases velocity and energy
    - - Corrosion or solution
      - Hydraulic action
      - Attrition
      - Corrasion or abrasion
      - Factors affecting rates of erosion
        
        Load
        
        Velocity
        
        Gradient
        
        Geology
        
        pH
        
        Human impact
  - - - evaporation
      - transpiration
    - - infiltration
      - throughflow
      - overland flow
      - base flow
    - - Precipitation of varying type and intensity
    - - soil
      - aquifers
      - vegetation
        
        throughflow
        
        stemflow
        
        interception
      - cryosphere
    - - Closed system
        
        no inputs or outputs, just stores and transfers
      - Open system
        
        inputs, outputs as well as stores and transfers
  - - - erosion at outside bend
      - deposition of point bar at inside bend
    - - raised banks at the edge of a river
      - built up from coarse material, such as sand and gravel
    - - by deposition in times of river flood
      - flat land bordering a river and made up of alluvium deposited during floods
    - - Heaviest material is deposited first and the lightest last
      - Distributaries form as the main river channel splits into smaller channels
      - Deposition occurs as the river loses velocity when it enters the sea
      - Delta is built up in layers
    - - Abrasion of soft rock by hard fragments
      - Lack of support by soft rock
      - Hydraulic impact
      - Weight of water causes unsupported hard rock to collapse
- - - - exposes soil to greater amounts of erosion => further erosion and gullying
      - causes sedimentation in the river channel => reducing the capacity and hydraulic efficiency of the river => increasing the likelihood of floods
      - reduces interception and transpiration - this increases the amount and speed of surface runoff => more water reaches the river faster
      - impact on a hydrograph
        
        Transpiration decreased
        
        Increased runoff
        
        Evaporation increased
        
        Storage reduced
        
        Lag time reduced
        
        Higher and steeper peak
        
        Faster recession limb
        
        Lower base flow
    - - Channelisation
        
        vegetation removed
        
        streamflow velocity increases
        
        if channel is too small => flooding
      - Levees
        
        if not maintained => can be breached => higher flood
        
        built to reduce flood risk
      - Bridges
        
        can increase upstream flooding
    - - Initial construction of houses, streets and culverts
        
        Decreased infiltration and lowered groundwater table; increased storm flows and decreased base flows during dry periods
        
        Sedimentation continues while bare ground is still exposed
      - Complete development of residential, commercial and industrial areas
        
        Decreased porosity, reducing time of run-off concentration, thereby increasing peak discharges and compressing the time distribution of the flow
        
        Greatly increased volume of run-off and flood damage potential
      - Removal of trees and vegetation
        
        Decreased evapotranspiration and interception; increased stream sedimentation
      - Construction of storm drains and channel improvements
        
        Local relief from flooding
        
        Concentration of floodwaters may aggravate flood problems downstream
    - - groundwater pumping
      - land management
      - reservoir operation
  - - - treatment of slopes such as contour ploughing or terracing to reduce the run-off coefficient
      - comprehensive protection of vegetation from wildfires, overgrazing and clear cutting of forests
      - reseeding of sparsely vegetated areas to increase evaporative losses
      - clearance of sediment and other debris from headwater streams
      - afforestation/ reforestation
      - construction of small water and sediment holding areas
      - preservation of natural water storage zones, such as lakes
    - - Flood relief channels => carry water when the river is in flood
      - Artificial levees
        
        most common form of river engineering
        
        the banks of the river are increased in height so that the river can carry more water and sediment
        
        also used to divert and restrict water to low-value land on the flood plain
      - Straightening the river => speed up flow and remove the water as quickly as possible
      - Raising the banks => hold more water
    - - hold back water during times of flood and release it when the flood risk has gone
      - can lead to increased loss of water due to evaporation, channel erosion downstream, a decline in sediments reaching the deltas, the spread of diseases like schistosomiasis and malaria
      - Reservoirs store excess rainwater in the upper drainage basin
    - - being prepared for the floods
        
        using sandbags
        
        sealing doors and windows
        
        moving valuables upstairs
        
        moving electrical generators to the top
        
        designing homes with higher level electrical features
      - Loss-sharing
        
        disaster aid
        
        insurance
  - - - reveals the relationship between overland flow and throughflow
      - where infiltration is low, antecedent moisture high, surface impermeable and rainfall strong, overland flow will dominate
    - - the seepage of groundwater into the channel - very important where rocks have high pore space
      - a slow movement, and the main, long-term supplier of the river's discharge
    - - time interval between peak rainfall and peak discharge
      - influenced by basin shape, steepness, stream order
    - - higher in larger basins
      - steep catchments have lower infiltration rates
      - flat catchments have high infiltration rates, so more throughflow and lower peaks
    - - very steep in a flash flood or in small drainage basins where the response is rapid
      - indicates the amount of discharge and the speed at which it is increasing
      - generally steep in urbanized catchments
    - - influenced by geological composition and behaviour of local aquifers
      - larger catchments have less-steep recessional limbs, likewise flatter areas
    - - the higher the rainfall, the greater the discharge
      - the larger the basin size, the greater the discharge
    - - GEOLOGY
        
        Impermeable rocks
        
        more closely packed => rainwater cannot infiltrate, surface runoff water reaches the river quickly => high peak and short lag time
        
        Pervious rocks
        
        allow water to pass through joints and porous rocks have spaces between pores => affect runoff response, intermittent flow in a river may result
        
        Permeable rocks
        
        absorb water quickly => surface runoff is rare => hydrograph peak is low and delayed
      - SEASONABILITY
        
        seasonal variations in temperature and evapotranspiration
        
        changes in vegetation cover
        
        the amount and nature of precipitation
        
        variations in rock types, soil types and the shape and size of the drainage basin
- - - - an extended period of dry weather leading to conditions of extreme dryness
      - impacts
        
        increased illnesses in humans
        
        increase in forest fires
        
        hosepipe bans
        
        increased animal mortality
        
        reduced crop yields
        
        private gardens watering/ carwash ban
    - - Water quality
        
        water infrastructure
        
        cost of water
        
        water availability
      - Water quantity
        
        evaporation
        
        the use of water by plants (transpiration)
        
        rates of rainfall
        
        river and groundwater flows
    - - Physical water scarcity
        
        where water consumption exceeds 60% of the useable supply
      - Economic water scarcity
        
        where a country physically has sufficient water to meet its needs, but requires additional storage and transport facilities
- - - - the process of coordinating conservation, management and development of water, land and related resources across sectors within a given river basin
    - - Any activity that takes place in a river basin has impacts downstream
    - - Conflict between stakeholders
      - Lack of data (on climate statistics, stream discharge and flood history)
      - Insufficient funding
      - Too much focus on financial costs/ benefits instead of on social needs
  - - - purify and filter harmful waste from water
      - nature's shock absorbers
      - guarantee our food supply
      - critical for biodiversity
      - store carbon
      - create sustainable products and livelihoods
      - ensure fresh water for all of us
  - - - Ensure availability and sustainable management of water and sanitation for all
    - - Balance the cost of water to support benefits of changing to use grey water, making this use easier
      - Changing habit to reuse/ recycle water
      - Prevent water pollution
      - Use water harvesting in homes - changing regulation for tanks in some areas - encouraging tank use to water gardens, reducing demand on treated pipe supplies
    - - Use dishwashers/ washing machines only when full, on eco setting
      - Change to metered water - increases awareness of consumption
      - Fix dripping taps
      - Lower flow rate on taps, efficient closure of taps
      - Smaller capacity bath/ smaller toilet cisterns
      - Bath => shower => shorter shower