Summary DSE Geo C2 Managing river and coastal environment

**C2 Managing river and coastal environment**

**DSE notes in bitesize**

1 - Key terms for uvial (River-related) studies

Key terms in water cycle:

- Precipitation
- Condensation
- Evaporation
- Transpiration
- In ltration
- Percolation
- Surface run-o
- Channel run-o
- Interception
- Drip ow
- Stem ow
- Through ow
- Ground water ow

Key terms in drainage basin:

- Main stream
- Tributaries
- Con uence
- Watershed
- Source of river
- Mouth of river
- Distributaries

Four types of drainage patterns:

- Dendritic (Tree branches-like)
- Radial
- Trellis (Square-like)
- Rectangular

2 - Factors a ecting the energy of a river

Key formula:

Energy of a river = Velocity + Volume

Factors a ecting the volume:

1. Precipitation and amount of snowfall

2. Gradient of drainage basin

3. Permeability of rock

4. Vegetation cover

5. Drainage density (Number of tributaries)

Factors a ecting the velocity:

1. Channel gradient




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, 2. Channel roughness (Friction - Measurement of wetted perimeter濕周)

3. Channel shape (Sinuosity 彎曲度）

3 - External processes (Erosion, Transportation, and Deposition) in rivers

Erosion in rivers:

- Hydraulic action (Water exerting pressure to river bed and banks, making them break o )
- Abrasion (River load grinding river bed and banks)
- Attrition (Load grinding one another)
- Solution (Soluble minerals dissolving in water)

There are THREE directions of erosion in rivers, which are 'Headward erosion', 'Vertical erosion /
Downcutting', and 'Lateral erosion'.

Transportation in rivers:

- Traction (Load being transported by rolling downstream slowly)
- Saltation (Load being transported by bouncing downstream)
- Suspension (Load being transported by owing downstream quickly)
- Solution (Soluble minerals dissolving in water)

Deposition in rivers:

- Sorting (Sediment is deposited according to their size, Largest load deposits rst while nest
load deposits at last)

Aim high (L4 or above) - Factors a ecting the rates of erosion, transportation, and deposition -
Please refer to the revision notes.

4 - Landform features in di erent river courses

Upper course:

- Interlocking spurs and deep V-shaped valley (Formation: Vertical erosion)
- Rapids (Formation: Water owing bands of more and less resistant rocks)
- Waterfalls and plunge pools (Formation: Less + more resistant rocks -> Hydraulic action +
Abrasion)

Middle course:

- Meanders (Formation: Active lateral erosion making the river channel even wider than before)
- Slip-o slopes (Formation: Deposition occurring in inner banks)
- River cli s (Formation: Lateral erosion happening in outer banks)
- Blu s (Formation: Retreat of river valley due to the expansion of meanders)

Lower course:

- Meanders
- Oxbow lakes (Formation: Continuous lateral erosion making two outer banks connect with each
other. The old channel will be sealed o )
- Braided streams (Formation: Low volume of water + Abundant supply of sediment during dry
seasons making river beds to surface)
- Floodplains and levees (Formation: Repeated ooding and sorting processes)
- Deltas (Formation: River energy drops at the mouth of rivers)

5 - Human activities in rivers of Hong Kong





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