Managing River Catchments

Managing River Catchments

1. River stability and change

   • effective discharge
     • magnitude/frequency analysis
       • criticized for treating transport rates as smooth and continuous
         • high variability so can't be universal
       • good for conceptual understanding
     • transport effectiveness attains a max value at some discharge
     • river morphology depends upon sediment discharge
     • assumes long-term equilibrium
   • river system characteristics vary so management should reflect this
   • magnitude of natural change needs to be understood
   • river response to disturbance can be complex
   • most important aspect of sendiment transport is sediment available from source
     • sediment transport in non-linear
       • therefore more responsive
   • supply-limited
     • i.e stream power is not fully utilized
     • critical importance to managers
   • Aims of restoration
     • improved habitat
     • improved oxygenation
     • rise in water table
     • increased stability
     • increased flooding
     • pre-disturbance state

2. Ecohydraulics

   • River continuum concept
     • drainage basin as a systematic physical whole
     • interconnected transport system
     • each feature has a significance in the system

3. Managing extremes

   • Probable Maximum Flood
     • conceptual tool for planners
     • lot of uncertainty
     • historical events
     • finite amount of rainfall
     • manage how we cope with it
     • political
     • return period for this is a pointless debate
       • earth's climate isn't stable
       • small but not zero probability
   • 1 in 100
     • more extreme
       • now 1 in 200
     • pragmatic and simple approach
   • Climate change
     • Increase p will cause increased erosion
       • time-dependent
         • could happen before p reaches river therefore cause accretion
     • change in land-use complicates it
     • idea of supply-limited is important
       • typical in Scotland
       • what is a result of CC is difficult to distinguish
     • biased sample in the literature
     • trends rather than events
     • seasonality is changing

4. Climate Change and Water Quality

   • probalistic approach
   • change in p doesn't DIRECTLY result in an increase in discharge
     • complicated by anthropogenic influences
     • limited sediment supply
     • time dependant
     • spatial diffusion of drainage networks
     • because discharge is variable, there is more extemes
       • more accretion or more erosion
   • non-stationary effects on discharge from climate change
     • important implications for...
       • flood risk
       • aquatic habitat
       • stability of infrastructure
       • channel sediment budgets
       • longitudinal profiles
       • overall impact

5. Legal Frameworks

   • EU Water Framework Directive
     • controversial
     • ecological status is not a fixed definition
       • Moss, 2008
       • continuous change to build resistance to change
     • redundant with CC?
   • SEPA
     • decided a single RBC was appropiate
       • Scottish Rivers are variable

6. seasonality of flooding is an integral aspect of flood managment

   • seasonality derived flood-frequency magnitudes
   • has considerable spatial variation
     • must take account of the time of year of peak rainfalls
     • soil moisture deficts
       • has a strong gradient from west-east
       • usually mitigate the risk in summer
         • Summer 2007 floods
   • most floods in the UK occur between October-March

7. linked to sediment sources

   • catchment management is central to sediment
   • morphology responds quickly to changes in upland areas