Rivers

Rivers

1. hydrological cycle

   • Inputs
     • Precipitation
   • Outputs
     • Evapotranspiration
     • River Discharge
     • Evaporation
     • Transpiration
   • Stores
     • Surface Storage
     • Channel Storage
     • Interception Storage
     • Vegetation Storage
     • Groundwater Storage
   • Transfers/Flows
     • Condensation
     • Throughfall
     • Surface Runoff
     • Infiltration
     • Throughflow (fast)
     • Interflow (medium)
     • Stemflow
     • Percolation
     • Groundwater flow
     • Baseflow (slow)
     • Channel flow
   • Water Budget Graph
     • wet seasons
       • precipitation exceeds evapotranspiration
         • ground stores fill,higher surface runoff and higher discharge
           • WATER SURPLUS
     • dry seasons
       • precipitation lower than evapotranspiration
         • ground stores depleted as water is used, but not replaced
           • WATER DEFECIT

2. storm hydrographs

   • Physical Factors
     • Drainage Basin Charecteristics
     • Antecedent Conditions
     • Rock Type
     • Soil Type
     • Vegetation
     • Precipitation
     • Temperature
   • Human Factors
     • Urbanisation
     • Man Made Drainage Systems
   • Typical Hydrograph
     • Peak Discharge
       • when rivers discharge is at its highest
     • Lag Time
       • delay between peak rainfall and peak discharge
     • Rising LImb
       • represents the rapid increase in discharge from rainfall as more water flows in
     • Falling Limb
       • represents the decreasing discharge as less water flows into the river

3. rejuvination

   • Isostatic
     • movement of land
   • Eustatic
     • change in sea level
   • change in base level
     • tectonic OR climatic
     • positive change: sea level rises due to glacial melt/sinking land
     • negative change: sea level falls due to glaciation or land rise due to tectonic activity

4. processes

   • Erosion
     • Abrasion
       • eroded pieces of rock scrape and rub against the bed and banks, removing material
     • Attrition
       • eroded rocks smash into each other and make smaller fragments, becoming rounded off
     • Corrosion
       • dissolving of rock through chemical processes
     • Hydraulic Action
       • the pressure of water breaks rock particles away from the bed and banks
   • Transportation
     • Bedload
       • material transported by traction/saltation
     • Suspended Load
       • carried with the body of water, fine to medium load are held by suspension
     • Dissolved/Solution Load
       • soluble material carried as chemical ions
     • Traction
       • large particles are rolled along the river bed by water moving down stream
     • Saltation
       • small stones bounce along the riverbed by water moving down stream
     • Solution
       • substances that dissolve are carried in the water
     • Suspension
       • very small particles carried along by the flow of water
   • Competence
     • total load a river can transport at a given point
   • Deposition
     • increased evaporation/abstraction causes lower discharge
     • friction reduces speed
     • when river is forced to slow down
     • when energy is lost meeting the sea
   • Hjulstrom Curve
     • shows relationship between competance and velocity

5. erosional landforms

   • Rapids
     • steep sections with turbulent flows pass over bands of dipping resistant rock
   • Waterfalls
   • Potholes
     • river is swirled around irregularities in the river bed creating verticle eddies
       • rocks are swept into small depressions and abrade the hollow, causing it to become deeper and enlarge
   • Braided Channels
     • climate, geology, topography combine and generate periodic high sediment loads
       • rapid deposition of coarse material blocks main channel
         • divide occurs forming sub-divisions of converging and diverging channels, then they rejoin
   • eddys
     • fluid current whose flow direction differs from the general flow

6. depositional landforms

   • Flood Plains
     • rivers fill over at bankfull, increasing wetted perimeter
       • more frictional contact and lower velocities cause deposition of fine sediment
         • increases fertility and height of plains as alluvium is added
   • Levees
     • parallel banks of sediment build up as heavier sediment is deposited closest to the channel
   • Deltas
     • sediments deposited at the mouth of river
       • alluvium material builds up until it rises above sea level
         • river braids into distributries to reach sea
   • Meanders
     • straight channels deposit sediment in alternating bars, creating riffles
       • occurs when there are low flows an low hydraulic radius, causing deposition
         • water flows around the high friction areas, creating a variation in flows, creating a side to side motion
           • helicoidal flow moves material from outside to inside , at high flow water undercuts the opposite bank due to centrifugal force
             • water enters meander at the faster outside edge, so less friction upon water
               • inside bend is shallower so more friction in river bed slowing it down
                 • river clif/bluff forms on the outside bend by erosion (hydraulic action and abrasion)
                   • critical deposition velocity occurs and deposition occur, creating a slip off slope
                     • helicoidal flow causes river to mover laterally across the flood plain
   • Oxbow Lakes

7. flooding

   • Factors Affecting Flooding
     • Human Factors
       • Deforestation
       • Urbanisation
       • Flood Management Stratergies
       • Climate Change
     • Physical Factors
       • Impermeable ground
       • Drainage Basin Type
       • Gradient of Slopes
   • Flood Management
     • Hard Engineering
       • Structural
         • Intercepting Channels
         • Channel Enlargement
         • Flood Relief Channels
         • Intercepting Channels
         • Flood Storage Reservoirs
       • Channel Improvements
         • Relief Channels
     • Soft Engineering
       • River Basin Management
         • Flood Plain Zoning
         • Flood Abatement
         • Flood Proofing

8. Channel Characteristics

   • Upper
   • Lower
   • Middle
   • The Bradshaw Model
     • demonstrates the changes expected as characteristics change down stream
       • triangle increases left to right, which means it increases as you go down stream

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