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Water Resources – Lecture 2:
The river environment:
River Geomorphology and Chemistry
River Morphology:
The Long Profile of a river
Steep Slope, low
deposition: mostly
suspended load
River
Morphology:
Channel
Pattern
Gentle Slope, higher
deposition, mixed:
suspended and bedload.
Mostly Bed-load.
From Morisawa, 1998
Two or more channels
with large stable
island: Suspended
load.
Riparian Zone
River Morphology:
Channel Profile
Channel Bank
River Channel
Bedload
Streamflow
Dynamic Equilibrium
• A river is a system is in a state of equilibrium, and is
continuously adjusting to changes in that system.
• What changes:
–
–
–
–
–
–
longitudinal profile,
channel profile,
river bed,
pattern (straight or sinuous),
depth,
velocity
• How does it change: Erosion and Deposition (aggradation,
degradation).
Physical Characteristics of river zones:
Upper Reaches
Slope
Steep
Velocity
Fast
Substratum
Mainly Boulders
Temperature
Low
Turbidity
Clear, Low
Solar Radiation
Low
Riparian Vegetation
Canopy Like
(Characterisation from Dallas and Day, 1993)
Upper Reaches
Physical Characteristics of river zones:
Middle Reaches
Slope
Gradual
Velocity
Slower
Substratum
Mixed boulders and sand
Temperature
Slightly Warmer
Turbidity
Intermediate
Solar Radiation
Intermediate
Riparian Vegetation
Concentration on banks
Middle Reaches
Physical Characteristics of river zones:
Lower Reaches
Slope
Gradual
Velocity
Slow – depositing
Substratum
Sand and Mud
Temperature
Warm
Turbidity
High
Solar Radiation
High
Riparian Vegetation
Only on banks, often exotic
Lower Reaches
Basics of Water Chemistry in Hydrology
• Important Physical Attributes of water:
–
–
–
–
Temperature (°C)
Suspended Solids (TSS mg/l)
Turbidity (function of TSS NTU)
Light Penetration
Basics of Water Chemistry in Hydrology
• Important Chemical Properties:
– [O2] mg/l
– pH
– Salinity [ions, in mmol/l] (Na, Ca, K, Mg, Cl, HCO3
SO4)
– Nutrients [mol/l] (Nitrates, Nitrites, Phosphates)
– TDS (total dissolved solids) (mg/l, essentially from
bedrock)
– Natural Organics
– Minor Organics
– Heavy Metals
Basics of Water Chemistry in Hydrology
• Particulate Inorganic Matter
– Silts and Clays: highly charged, and therefore
remain in suspension.
• Particulate Organic Matter
– Shredded Leaves (Generally Coarse Particulate
Organic Material {CPOM})
– Dead organic material (Fine Particulate Organic
Material{FPOM})
– Bacterioplankton, Plankton.
Chemical Characteristics of River Zones:
Upper Reaches
Dissolved Oxygen
High
Nutrients
Low
Conductivity
Low
pH
Low
Organic Material
CPOM
TDS
Low
Chemical Characteristics of River Zones:
Middle Reaches
Dissolved Oxygen
Intermediate
Nutrients
Intermediate
Conductivity
Increases
pH
Increases
Organic Material
CPOM and FPOM
TDS
Intermediate
Chemical Characteristics of River Zones:
Lower Reaches
Dissolved Oxygen
Low
Nutrients
High
Conductivity
High
pH
Higher
Organic Material
FPOM
TDS
High
Photo: Kate Rowntree
Mhlatuzi Case Study
• Strategic Environmental Assessment
– SEA is a systematic process of addressing the
environmental considerations and consequences
of proposed policy, programme or plan
initiative, where:
• Policy refers to the framework which guides any
subsequent decision making.
• Plan refers to the strategy for implementing the
policy.
• Programme refers to the schedule of proposals,
commitments instruments and activities.
Questions Regarding Mhlatuzi Case Study
• To make a strategic assessment of water needs and
allocations, what type of information do you need?
• How is water valued in this catchment in economic terms,
in social terms, in environmental terms, and in political
terms.
• The SEA team argue that the greatest biological diversity
in the catchment is to be found in the undeveloped rural
areas. Allocating water for the development of this region
could lead to the loss of that biodiversity. How can this
issue be resolved?
• If water is allocated to sectors where it will be used most
economically, will this also be socially and
environmentally optimal?
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