Freshwater - Drainage Basin

Drainage Basin hydrology and geomorphology

A drainage basin is an area of land on which precipitation falls and that water is drained into oceans. A drainage basin is an open system

Inputs

Outputs

Stores

Evaporation

Evapotranspiration

Potential Evapotranspiration - dependent on moisture availability and water content of soil

Vegetation

Soil

Aquifers

Cryosphere - the snow and ice environment

Flows

Infiltration - water soaking/being absorbed by soil

Overland flow

Throughflow - water flowing through the ground and soil

Base flow - throughflow flowing into the bed of a river increasing the discharge

Precipitation

Interception - water stopped by plants from entering rivers

Throughfall - water that falls through gaps in plants

Stemflow - water that trickles along stems and roots until it enters ground

Stream flow

Strength of flow subject to gravity, frictional resistance, shape of channel, depth of channel.

Velocity - velocity is the fastest middle of the river at a third of depth as it is away from the sides as has no surface friction

Channel shape - ideal shape is semicircular and can be measured by calculating the wetted perimeter

Channel roughness - can be increased by irregularities of rock, vegetation, trees etc.

River processes

Erosion

Factors determining rate of erosion

Load

Velocity

pH - increased acidity aids with erosion

Gradient - increased gradient increases rate

Human impact - interference with the flow of water can lead to increased rate

Geology - softer rock is eroded faster

Abrasion

Attrition

Hydraulic Action

Solution

Methods of transport

Saltation

Solution

Traction

Suspension

image

River regime - annual variation of flow within a river - influenced by amount of precipitation, permeability of rocks, amount and type of vegetation cover

Land formations

Waterfalls 1. Hard rock overlays soft rock 2. The soft rock is undercut by hydraulic action and abrasion 3. The lack of support causes the overlaying hard rock to collapse and fall. 4. This and the constant slamming of water vertically create a plunge pool. 5. This process repeats and creates a gorge over time

Floodplains 1. When river slows down and alluvium and silt is deposited

Levees 2. Over hundreds of years, silt and finer material is deposited further away, while coarser material is deposited closer. This eventually builds up a barrier where the river can no longer flood.

Meanders

Oxbow Lake

Delta - river sediments being deposited as a river reaches it's mouth

the amount of size and load - greater the load and size larger the delta

salinity of water - salt and clay stick together increasing load size and increasing deposition

vegetation will slow water and increase depositon

delta normally forms more on gentle coastlines

Flooding and Flood Mitigation

Hydrographs

Hydrograph Size

Larger the rainfall, larger the hydrograph

Larger the basin, larger the hydrograph

Factors which impact flashiness of hydrograph

More flashy

Higher drainage density

Used for industry, dam built

Thin grass, moorland

Urbanisation

Impermeable rock

Very thin soil

Steep slopes

Less Flashy

Lower density

Limited use of river

Forest

Rural area

Permeable rock

Deep soil

Gentle slopes

Urbanisation and it's effects

Urbanisation tends to affect flood risk more in the lower course than upper course as urban areas are generally found on flatter terrain

Removal of trees - decreased evaporation, transpiration, evapotranspiration, transpiration

Construction of houses - decreased infiltration and lowering of water tables meaning water must travel deeper

Development of commercial areas - this leads to decreased soil permeability

Storm drains - water enters river faster

Channel modification tends to increase flood risk as water will enter the channel a lot faster

Flood prediction and mitigation

Improving flood warnings

improved rainfall and snowfall estimates, better and further in advance forecasts of rainfall

better mapping of rivers and channels

improved demographic information collection to better assess flood risk

better distribution of information to news agencies, more timely information distribution

improved technology of forecasting news agencies

Amelioration of floods

Disaster aid

Insurance

Event modification

Flood abatement

reforestation

protection of vegetation

revegetation

clearance of sediment/debris from streams

construction of floodable areas/water storage zones

Flood diversion

into rivers

into lakes

into reservoirs

See Study Guide for Channel Modification

River modification

Straightening the river which lessens friction and speeds up velocity

Heightening the banks to decrease flood risk

creating flood relief channels

Water scarcity and Water quality

Environmental impacts of agricultural activities

Irrigation - Addition of water where there is insufficient for crop growth. This can result in changes in precipitation, inefficient use of water, and the water table will lower significantly.

Salinization - increase in amount of salt in soil, when groundwater reaches the surface and capillary forces bring water to the surface where it evaporates leaving behind the salts

Eutrophication - fertilizers leak into water, this leads to increase in plant and algal growth, algal bloom results in lack of sunlight reaching plants because it covers surface, results in plants dying, bacteria decompose the plants and use up all the oxygen, without oxygen the water is dead-zoned

many people suffer the consequences of this such as the farmers who are damaging the water, governments who want to keep water clean but also need to increase food production by use of fertilizers, and consumers who are trading food for lack of clean water.

Human impacts

Increased urbanization

more population dense so increase demand for water

more water required for agricultural use so more water on tap is required

Population growth - more people need more food which means more water and more agriculture which is inefficient water use

Acidification of lakes by sulfur, nitrogen and other chemicals

Water management and futures