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Monday, 14 November 2016

The shrinking lagoon


They say a picture speaks a thousand words....


This photo was taken in March 2015, looking westwards into the lagoon from the bund bridge.


This one, and the next one, were taken on the work day last Saturday, standing in the same spot.




2 comments:

Steve Blacksmith said...

Hi Birdbox,
Is it really surprising that the lagoon has dried up from March to November?

The reason there is a lagoon is because the farmland on the banks of the Calder was sacrificed to the gravel-extraction industry.

Then the gravel pits were used to dispose of fly-ash from the former Elland Power Station.

Then the fly-ash itself was taken away when the civil engineers realised they could use it for road building.

So we have the remnants of a fly-ash tip in a gravelly hollow in the ground. There must be a porous fly-ash/gravel layer between the river and the lagoon, I surmise.

If the river level could be raised, this might raise the level in the lagoon.

The nearest weir is just below Avocet. If the lip of this weir could be raised, it would raise the level of the river opposite the nature reserve, and the level of the water in the lagoon(s).

I heard at a recent meeting David L. talking about mechanically stripping out areas of the lagoon (regarding control of the Crassula helmsii plant) and I would wholeheartedly agree with this. Far more interesting birds were attracted to the lagoons when they were just recovering after the fly-ash extraction than we have now. I remember a Spotted Sandpiper particularly.

If mechanical stripping could be carried out over various parts of the reserve, both dry and wet parts, on a rotational system, I'm sure the whole biodiversity would be enriched.

At the moment the natural tendency of the whole reserve is to go through the progression into high woodland. We won't see the process of re-greening from bare soil through mosses, then flowering plants, then shrubs, unless more radical scraping back is carried out.

Allan said...

Many thanks Steve for your comments and contribution how we approach the issues regarding the lagoon which were higlighted in a report published in 2005. The report stressed a number of important issues, not least the problem of scrub encroaching into the lagoon and the need to bring in water from either the canal,river or a bore hole.

Since then, the issue has got worse.

The issue of how the Cressula is dealt seems to be a complext one. Mechanical removal does not seem to be something that YWT would recommend (They suggest chemical treatment.) How woud that then effect the reed bed? Given how widespread the Cressula is ( it is even in the wet woodland) tackling the problem is, in my opinion, something only CMBC can lead on. According to the YWT website on the issue you only need a few strands left on site and it will begin to spread again.

At CBWG we are discussing all of these issues because we hope to get a grant that would deal with the incursion of the trees and bring in water using one or a combination of the sources outlined in the 2005 report.