The Hydrological Cycle:
1) Homework Task:
Complete the global hydrological cycle worksheet from geographyalltheway.com
The Drainage Basin:
Features of a Drainage Basin
Drainage Basin Vocab:
Drainage basin: The area drained by a river and its tributaries. A drainage basin is considered to be an open system because water can be added or lost from a drainage basin.
Source: The beginning of a river. A river may have multiple sources. The source of a river is normally found in upland mountainous areas.
Mouth: The end of a river. A river may end in a lake, but more normally in the sea.
Tributary: A small river that flows into a larger river.
Confluence: Where two rivers meet.
Watershed: The border between two drainage basins.
Estuary: The tidal section of a river near the mouth.
Channel: The physical confines of the river, encompassing two banks and a bed.
Bank: The sides of a river channel. A river channel has two banks.
Bed: The bottom of a river channel.
2) A Visual Tour of the Rhine drainage basin.
We will be working from this interactive map of the Rhine Drainage Basin.
a) You can find a map of the Rhine and lots of photo’s in this folder. Either digitally or as a paper exercise, use the photo’s to create an illustrated guide to the Rhine drainage basin. You can use google earth and other tools to help locate the places in the photo’s.
The Drainage Basin System:
A drainage basin is an open system that has inputs, outputs, stores and transfers (flows).
Inputs: When water is added to a drainage basin.
Precipitation: Any moisture that falls from the atmosphere. The main types of precipitation are rain, snow, sleet, hail, fog and dew.
Interbasin transfer: Water that either naturally (due to the alignment of the rock) or with human involvement (pumps and pipes) moves from one drainage basin to another.
Outputs: When water leaves a drainage system.
Evaporation: The process of water turning from a liquid into a vapour. Evaporation only takes place from a body of water e.g. a lake, puddle or the sea.
Transpiration: The evaporation of water from vegetation.
Evapotranspiration: The combined action of evaporation and transpiration
Interbasin transfer: Water that either naturally (due to the alignment of the rock) or with human involvement (pumps and pipes) moves from one drainage basin to another.
River discharge via channel flow: Water entering the sea and leaving a drainage basin. A very small amount of water also enters the sea via throughflow and groundwater flow (baseflow).
Stores: When water is stationary and not moving in a drainage basin.
Interception: When water is caught and held by vegetation or man-made structures like buildings.
Surface store: When water is held in the surface of the earth. This may be a puddle, a lake or a garden pond.
Soil moisture store: When water is held in unsaturated soil.
Groundwater store: When water is held in saturated ground.
Transfers (flows): When water is moving within a drainage basin.
Stem flow: When intercepted water runs down the trunks and stems of vegetation.
Canopy drip: When intercepted water drips off the leaves of vegetation (drip tip leaves in rainforests are actually designed to allow this to happen).
Throughfall: Precipitation that falls directly through vegetation.
Infiltration: Water that moves from the surface of the earth into the soil below.
Throughflow: Water that travels through unsaturated ground.
Pipeflow: Water that travels through holes left by root systems and animals burrows.
Percolation: Water that travels from unsaturated into saturated ground.
Groundwater flow (baseflow): Water that travels through saturated ground.
Capillary action (or rise): Water that may move upwards towards the surface.
Channel flow: Water that travels in a river.
Surface run-off (overland flow): When water travels across the surface of the earth e.g. down a hill.
Long Profile.bmp
Hydrographs
Task:
Now work through this An excellent interactive guide to drainage basins and hydrographs
Complete this flood hydrograph worksheet from geographyalltheway.com page.
The factors that effect the shape of hydrograph:
Rock and soil type
· Permeable rocks ad soils (such as sandy soils) absorb water easily, so surface run-off is rare
· Impermeable rock and soils (such as clay soils) are more closely packed. Rainwater can’t infiltrate, so water reaches the river more quickly
· Pervious rocks (like limestone) allow water to pass through joints, and porous rocks (like chalk) have spaces between the rock particles
Land use
· In urban areas, surfaces like roads are impermeable – water can’t soak into the ground. Instead, it runs into drains, gathers speed and joins rainwater from
other drains – eventually spilling into the river
· In rural areas, ploughing up and down (instead of across) hillsides creates channels which allow rainwater to reach rivers faster increasing discharge
· Deforestation means less interception, so rain reaches the ground faster. The ground is likely to become saturated and surface run-off will increase
Rainfall
· The amount and type of rainfall will affect a river’s discharge
· Antecedent rainfall is rain that has already happened. It can mean that the ground has become saturated. Further rain will then flow as surface run-off towards the river
· Heavy continual rain, or melting snow, means more water flowing into the river
Relief
· Steep slopes mean that rainwater is likely to run straight over the surface before it can infiltrate. On more gentle slopes infiltration is more likely.
Weather conditions
· Hot dry weather can bake the soil, so that when it rains the water can’t soak in. Instead, it will run off the surface, straight into the river.
· High temperatures increase evaporation rates from water surfaces, and transpiration from plants – reducing discharge
· Long periods of extreme cold weather can lead to frozen ground, so that water can’t soak in
(from http://www.acegeography.com/factors-affecting-river-discharge-gcse.html)
Drainage Basin Management:
Look at the map you have just produced. Why might their be problems with the management of the Rhine’s drainage basin?
The Mekong
An excellent example of the difficulties of drainage basin management is the Mekong in Southeast Asia. Read this article and summarise the issues around the management of the Mekong.
Suggest some possible solutions to the management problems and the difficulties that may be faced from their implementation.
Why do you think it has proved much easier to manage the Rhine than the Mekong?
