Water Levels at the Flashes
As spring progresses the hope of passage waders arriving is always at the forethought of many local birders. It is also the time of year when the perennial question of why is the water so high, is on many people’s lips.
I will try and explain the rationale as to why the water is kept higher than people would want or expect it to be.
Firstly the Flashes as a whole are very shallow and the only way of topping them up is by rain water although the water is shallow the mud is very thick and treacherous . As the water is highly saline, very little vegetation grows in or around the pools apart from a few salt tolerant species of plant. So a small drop in the water level can expose a surprisingly large expanse of mud. However a larger drop of the level does not mean that more mud would be exposed exponentially.
It is important that each time the water is dropped the exposed ‘wet’ muddy period is maximized for the feeding waders, very similar to how the ebbing tide in an estuary is utilised by waders only over a much longer time period. As the mud dries out the water is dropped again to expose new muddy areas. But when it rains the mud becomes wet and at this point it is as if the tide is coming in and the water level rises once again. This gives us a chance to repeat the whole procedure and prolongs the period of maximum wader feeding potential.
However if the water is dropped too low and no rain is available to replenish the level, problems occur. These include the mud baking rock hard and forming a salty crust devoid of life and making it impossible for burrowing invertebrates to emerge. If the water drops too much the ‘safety aspect’ for the birds of the breeding islands is compromised.
Due to the salinity of the water when the exposed mud dries it can bake as hard as concrete and even if rain occurs it just sits on top and will soon evaporate in hot conditions.
We have used the water level marker as a guide to what height the water should be relative to the time of year. It is not definitive and weather forecasts are integral to the success of the scheme.
Just to reiterate spring levels are monitored to allow mud to be exposed for the short duration of wader passage. The exposed muddy conditions are then maintained to a level conducive to wader chick rearing. Finally if we got things right the protracted Autumn wader passage will see ideal conditions from August to October when the water level will be at its lowest and the threat of a complete ‘dry out’ will have diminished. The pool has dried out within the last 6 years and the knock on effect sees the following year’s food supply (of invertebrates) depleted and thus a poor show of waders. The name of the game is CAUTION
The photo show the effect of varying levels
1.2nd May 09 (water level = 0.5)
2. 27th June 09 (w/L = 0.42)
3. 11th August 09 (W/L = 0.42)
4. 19th September 09 (W/L = 0.35) on next page it didn't upload
5. water levels relative to the time of year - this was taken from the management manual of 1998 (SC/JTB)
B
John
