Option A - Drainage basin hydrology and geomorphology Flashcards
Drainage basin
an area within which water supplied by precipitation is transferred to the ocean, a lake or a larger stream. It includes all the area drained by a river and its tributaries
Freshwater
includes rivers, lakes, wetlands, groundwater, glaciers and ice caps.
Source
the area in which a river begins
Mouth
where a river ends its journey, flowing into the sea or a lake
Tributary
a smaller river that joins a larger river
Confluence
the point at which two rivers join
Watershed
the boundary between two drainage basins marked by a ridge of high land
Drainage density
the total length of all the streams in the basin divided by the total area of the basin.
The hydrological cycle (water cycle)
the continuous exchange of water between land and the atmosphere. Approximately 97% of the Earth’s water is stored in the oceans, and only a fraction of the remaining portion is usable freshwater.
River discharge
the volume of water passing a given point over a set time.
Bradshaw model
a theoretical model that helps describe the chanegs we would expect as a river travels from its source region in its upper course with increasing distance downstream.
Name the changes as the river flows downstream for: velocity, discharge, width and depth, gradient, load, wetted perimeter and channel bed roughness.
velocity generally increases downstream as more water is added to rivers via tributary rivers.
discharge increases downstream as tributaries swell the amount of water and velocity increases as channels become smoother and less rough
width and depth increase downstream as more water is added from tributaries
gradient decreases as rivers flow because the river meanders across the land rather than erode into it and follow a straight path as it does in the source.
load decreases downstream and the stones get rounder and smoother as they are eroded
wetted perimeter increases downstream as water feeds into main streams from tributary rivers
hydraulic action increases as the stream should increase in size and thus power
channel bed - Less rough/turblent downstream due to erosion
Erosion
involves the wearing away of rock and soil found along the river and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.
Four types of erosion
corrasion/abrasion
corrosion
hydraulic action
attrition
Corrasion/abrasion
the wearing away of the bed and bank by the load carried by a river.
Attrition
the wearing away of the load carried by a river. It creates smaller, rounder particles.
Hydraulic action
the force of air and water on the sides of rivers and in cracks.
Corrosion/solution
the removal of chemical ions, especially calcium.
Factors that affect rates of erosion
load gradient pH geology velocity human impact
Vertical erosion
when the river cuts down vertically into the ground to create a V-shaped valley
Lateral erosion
when a river erodes laterally (sideways) across the valley, creating a flat valley bottom.
Methods of transportation in river
traction
saltation
suspension
solution
Traction
larger boulders and rocks are rolled along the river bed.
Saltation
small pebbles and stones are bounced along the river bed
Suspension
fine, light material is carried along by the river
Solution
minerals are dissolved in the water. This is a chemical change.
Deposition
the geological process in which sediments, soil and rocks are added to a landform or land mass because the water losses energy and is forced to drop them.
Waterfall
water dropping from a higher to lower point, sometimes a great height, from a river or stream
Formation of waterfall
The soft rock is undercut by hydraulic action (force of air and water on the sides of rivers and oceans)
Abrasion of soft rock occurs
Lack of support by soft rock
Weight of water causes unsupported hard rock to collapse and retreat
Flood plains
areas of low relief formed by deposition when a river floods.
Meander
a winding curve of bend in a river
Oxbow lake
a U-shaped lake that forms when a wide meander from the main river is cut off
Formation of meanders and oxbow lakes
Due to banks of sediment at the bottom of the river (deposited at times of low flow), the river weaves around these alternating shallow and deeper sections on what was initially straight channel.
This movement targets one bank of the section leading to erosion (abrasion and hydraulic action) and becomes the outside bend of the meander.
Further erosion narrows the gap between the two arms of river. When it floods, the river breaks through narrow gap.
Eventually the neck of the meander will be breached by the river creating an oxbow lake.
Levees
embankments built to prevent the overflow of a river.
Formation of levees
During a flood, water overflows the river banks and existing levees until it reaches the end of the floodplain. Rocks, gravel, mud and smaller material is lifted up and transported onto the floodplains.
Deposition occurs - the bigger the material, the closer it is to the river bank, and vice versa with small materials. The material is deposited according to its size. Full deposition occurs when the water retreats - Horizontal Sorting.
After water has retreated, levees are created and the river level increases. It can also take material back to the river source and be deposited there. This is why the river may flow above the level of floodplain.
Braided channels
a channel that consists of a network of smaller channels separated by small and temporary islands called ‘eyots’ or ‘braided bars’.
Formation of braided channels
There is a build of sediment where water flow is slow - causes changes in the direction of the river and create new channels.
This can occur to form a delta - one type of braided channels.
Delta
formed when a stream flows into a standing body of water.
Formation of delta
A river needs to carry a large volume of sediment.
Deposition is increased if the water is salty (salt particles group together) and become heavier, so they are deposited.
