Hydrology, human stuff Flashcards
What is abstraction, why is it carried out?
Abstraction is the removal of water from a water body, such as a river, lake, reservoir, or groundwater store. This is carried out to meet water demand for drinking water, sanitation etc.
When is abstraction unsustainable?
Abstraction is unsustainable is when abstraction rate is higher than the replenishing rate, causing a water deficit.
What issues occur when water abstraction is unsustainable?
(Over-abstraction)
The water table may fall when groundwater is overexploited, meaning there is less groundwater seepage into above ground water stores, which may cause above-ground water levels to fall. This can decrease channel flow and discharge and may cause deposition. Too much sediment deposition can bury habitats and physically alter a waterway.
What is the function of a dam?
Dams directly stop and control channel flow, as they provide a barrier in the way of a river channel.
What is the effect of a reservoir being behind a dam?
Reservoirs behind dams can raise the water table underground in the area of the resevoir, and can increase soil saturation if not properly managed. This may lead to a lowering of the water table in other areas as the water that would normally be flowing in other areas in other is instead being stored in the resevoir.
Reservoirs are usually very large, what is the effect of this?
This means water can enter the atmosphere through evaporation and increase cloud formations in the area, increasing precipitation.
How can the probability of a flood of a certain size be predicted?
The probability of a flood can be predicted based on past flooding records. This known as a flood recurrence interval.
What are flood recurrence intervals and why are they important?
Flood recurrence intervals are a methods of presenting the probability of a flood of a given size in an given area. Recurrence intervals are in years. Flood recurrence is important when assessing the risk of flooding in an area. If the recurrence interval is longer, the probability of a flood of a given size is is smaller, therefore there is hypothetically less risk of a flood in that area.
What is flood forecasting?
(soft engineering)
Flood forecasting uses precipitation forecasts to estimate the level of flooding risk in an area. Streamflow data and models of streamflow routes can calculate the areas most at risk of flooding when heavy precipitation is forecasted, meaning warnings can be issued days before. Early warnings are vital in the preparation for flooding, as people can take action by evacuating, moving valuables and sandbagging.
What is an example of flood forecasting?
In the UK, the Met Office issues ‘amber’ and ‘red’ flood warnings so that people may act accordingly. An amber flood alter means ‘be prepared,’ whereas a severe (red) flood warning means ‘danger to life’.
How does channel straightening work?
Channel straightening is where bends and irregularities in the river channel are removed using machinery, leaving a straight channel (e.g. by cutting off meanders).
River channels are straightened to increase river velocity, meaning it is less likely for the river to overflow onto the flood plain and instead moves quickly downstream.
There can be issues with straightening channels, as water is just sent further downstream where it can cause flooding further downstream and enhance erosional processes such as abrasion and hydraulics (as it is high velocity).
How do diversion spillways work?
A diversion spillway is a constructed channel that allows excess water to flow into it when the channel is overflowing.
The spillway may direct water to further downstream, or it may direct water to a different river.
On many spillways, there are usually floodgates that control when they are opened and closed.
Spillways may direct water to areas that do not flood naturally, which can cause environmental damage if the spillway floods.
What are wetlands and why are they important?
Wetlands are ecosystems that are partially submerged in water for period of time, which limits the availability of oxygen and creates an environment for aquatic plants and animals.
Wetlands are very important to the river system, as they provide environments that flood water can inundate, which limits flooding elsewhere
Why are wetlands under extreme threat?
Wetlands are under extreme threat due to climate change as well as human impacts (such as draining to make land available agricultural use).
How can wetlands be conserved?
-Banning or limiting the drainage wetlands, to protect the ecosystem.
-Monitoring changes (such as water level changes, changes to seasonal flooding, changes to wildlife) so that actions may be taken to counteract these changes.
-Reintroducing species of plants and animals that may have been affected by past activities. By reintroducing native species, the natural balance of the ecosystem can be restored so that wetlands can continue to serve their purpose.
-In some cases, the conditions of wetlands may have to be recreated (e.g. there may be a lack of water due to a particularly dry season). Water from the river can be pumped into the wetlands, so that the ecosystem can continue to be stable until normal water levels are restored.
