The Presentation was by Nick Haycock, the hydrologist who spoke at KLPA AGM.
The talk was in two sections as he prefaced the main topic with some remarks clarifying legal issues relating to the plan to raise and strengthen the pond dams.
Part 1 Legal background relating to proposed works.
There are three relevant Acts concerned with reservoir safety dating respectively from 1932, 1975 and 2010. In addition the Corporation of London (CoL) has to be guided by the 1871 Act which guarantees preservation of Hampstead Heath as natural open space as far as is possible. This Act informs any major building and other works on the Heath as its managers legally have to try and maintain and conserve its natural character. This principle was applied to the recent renovation of the ponds at Kenwood, which were kept as far as possible in original Repton style. It will apply to the proposed work on the Heath ponds.
The 1932 and 1975 acts set down a stringent risk factor for dam design, which applies to three of the Heath ponds. The reason why work was not done previously in accordance with the 1975 Act is that in 1987 a survey estimated the risk of flooding as quite low. A key factor before the 2010 Act became an issue is that in 2006 a new study showed the 1987 one to be faulty as it failed to take account of the impacted nature of the much of the soil. Also at some point in the ‘80s the CoL lowered the water level in Highgate 1 pond in order to avoid it being deemed a reservoir under terms of 1975 Act. On the basis of the 2006 report the CoL began investigating work required to bring three dams up to the standards required by the 1975 Act and estimated the cost of the work at about £8 million.
Unless modified, the 2010 act will extend the safety requirements to all the ponds on the Heath. It is now not clear when it will be implemented and changes are possible. The CoL had been preparing plans based on the last Government’s timetable by which the Act would come into force in 2011. The obvious advantage of dealing with both acts at once is that disruption and costs would be reduced. It seems there is another advantage in that a plan for all the dams allows for work on the three dams affected by the 1975 Act to be less intrusive than if only those dams are strengthened. Under the 2010 Act they could treat the two chains of ponds as 2 units rather than dealing only with the highest risk ponds. This may mean work will be done on more ponds but less massive work on any one pond.
Currently the CoL is working on the double line of preparing plans to meet the 1975 requirements while hoping to be able to avoid implementing them until it becomes clear what will be demanded by the 2010 Act.
Part 2 Water Quality
Since 2006 there have been occasions when the coli form count for the swimming ponds has been above the recommended level.
There are two major problems:
1) high level of e-coli and other cyanobacteria and also of harmful algae
2) poor oxygenation, especially to the lower levels
1) is thought to be primarily due to dog faeces; other possible causes, like wild life excreta or the effect of bread being thrown into the water have been explored but dog faeces appears to be the main issue.
Because of the impacted nature of much of the Heath water absorption is poor; consequently, whenever there is rain the pollution from the faeces runs off and can reach the ponds.
An important factor is that since the mid 1970s dog food manufacturers have been adding calcium phosphate to dog food, which is entirely unnecessary for normal, well-fed dogs, and as a result the dogs excrete most of the phosphates which are then washed into the water when it rains. It is estimated that each year dogs deposit about 16 tons of excreta on the Heath of which only about one ton is put into the bins and removed. The result is that the phosphates are washed into the soil and the ponds after rain, absorbed by plants and recycled into the water again. Unfortunately, one of the effects of phosphorus is to encourage the growth of anything animate including algae and bacteria. This is probably the reason for the increased incidence of blooms of blue green algae (cyanobacteria) . While the e-coli dies after about 5 days exposure to sun the phosphorus remains and builds up.
It has been noted that the level of phosphorus contamination in the bird sanctuary pond is significantly lower, since the soil around it is not impacted and no dogs are allowed in the immediate vicinity.
2) Lack of adequate oxygen at the sediment surface prevents various aquatic species living, including planktons and can lead to smelliness.
This is connected to the phosphate problem because the blue green algae dies and sinks to the bottom forming a layer which discourages plant growth.
One solution would be to add chemicals but the CoL is unwilling to do this as it could damage the fish and upset the ecosystem. Adding oxygen is a better method. This can be done by bubble curtains and/or by re-circulating the water. Recirculation would be done with the proposed new dam system by pumping water back up from the cascades. To facilitate this system they would like to raise the water level in the Stock pond and the Aqueduct pond to have an increased reservoir to flow into the lower ponds.
There is also an ultra sound system, which is being used currently in the men’s pond. There are other systems, which have not yet been tried. One of which – Aqua 4D – is an electro magnetic system which the management hope to try.
Reed beds can help in encouraging home for planktons and other useful micro-organisms; but for them to be effective in maintaining water purity (this without the dog problems) you need about 1/8 each pond covered in reeds.
Barley bales may have some value but no-one is sure how they work; it may be a fungus on the straw which combats the algae.