When a water table rises
In a previous blog post we mentioned that a water table lies on the boundary between the land’s saturated and unsaturated regions. Therefore, it would be fair to infer that a water table lies beneath us, underground. However that is not the case.
So, what is the case?
The water table does not form exclusively underground, it simply follows the topography of the land. in some cases, a canyon or sloping hillside may expose an underground river or lake. Furthermore, the water table collects where it can go no further.Granite or other impermeable rocks will halt its natural downward movement, as will compacted soil.
In other words, a water table can be halfway up a hill
This is referred to as a perched water table and during periods of heavy rain or snow, water may permeate through to the water table, causing it to overflow. So, even if you have built a house high on a hill to avoid floods, it is entirely possible that you could still be flooded!
Why does the water table rise?
In the UK, the main cause of rising water tables is unusually high levels of rainfall. When this happens, the water table overloads and rises through the permeable substrates, forcing itself onto the surface.
The disruption can be catastrophic; homes being flooded, sewage pipes overflowing and even backing up into households – creating safety hazards and a severe risk of infection. There is a threat of contamination of the drinking system, not only from sewage but from other sediments brought up by the rise in water levels.
Rising water tables may cause damage to the transportation infrastructure, causing road traffic and trains to be suspended. This also impacts people who have been badly affected as much-needed medical supplies and food won’t be able to reach their destinations. Even the foundations of buildings can be weakened by rising water tables.
Rising water tables may also affect agriculture; whilst not enough water can kill crops, too much water can destroy them. In geographical regions which are heavily reliant on producing their own food, flooding can have a devastating effect.
What can be done?
An efficient drainage infrastructure works wonders. A well designed drainage system based on an accurate topographical map of the land has several huge benefits:
By quickly draining away excess water, the risk of excessive flooding can be reduced significantly. If the water level is too high then the water needs to be directed somewhere else. Holding pens and reservoirs will help to alleviate the problem.
If the area is in drought then the same drainage system will be an efficient way of replenishing the depleted water table. This has already begun to be utilised in the midwestern region of America to restock the Ogallala water table, or at least slow down the depletion of this natural resource.
If the problem becomes a national catastrophe then a series of dams in the heavily affected areas is perhaps the only solution, albeit an expensive one.
And I’ve not even mentioned global warming and the melting of the glaciers!
[Photo by kconners]