The Stangrove Pond Survey - 2006

Stangrove Pond Slide Show

Overview of the pond

The word pond has the same derivation as pound, an enclosure, in this case of water. Exactly where a pond ends and lakes begin is a rather blurred area. Some authorities state that anything larger than four acres is a lake, regardless of depth, others say that a pond is any body of water, of less than three metres in depth, where sunlight may penetrate to the bottom. All are of the opinion that it must be an area of still water, although many ponds have streams flowing through them! Whatever the arguments, I think that we may be sure that what lies before us here is very much a pond and nothing else!

The origins of the pond in Stangrove Park are unknown, as are its age, at least to me. Neither the park, nor the pond, appears on the first ordinance survey map of 1840. It seems unlikely that it was dug as a source of clay for building, or as a stew pond, or that it was an enclosure pond, although it is perfectly possible that it may have served as a reservoir to a farm, or whatever, prior to the area becoming a park.

My own view, and it is only an educated guess, is that Stangrove Park, together with this pond, dates from around 1850 and that it has always been an ornamental feature, perhaps doubling as a water source for the surrounding park. A clue lies in the Wellingtonias growing close by (hence Wellingtonia Way), these were unknown in Britain before about 1846 (about the same time as the demise of Arthur Wellesley, AKA The Duke of Wellington, whose name they now bear in this country. In America, of course, it is the big tree, or giant sequoia) and to have grown to their present size they cannot be much younger than that date, when they rapidly became popular as exotic specimens in town parks and the grounds of stately homes. I imagine, therefore, that our pond is probably contemporary to this period, assuming that the trees were planted at the same time as the park came into being.

Local opinion suggests that the pond is stream fed from below the water line, which, although I am neither a geologist nor a water engineer, would, I fancy, result in a constant overflow via the outlet pipe if it were of a lined construction, using puddled clay, as I originally thought it might be back in 1993. Conversely, without an inlet of any kind it would surely dry up completely during the summer months, due to evaporation and the respiration of surrounding trees.

Looking at the way it is formed, as a sunken hollow, with the water level well below the surrounding landscape, I now believe that it is maintained by the ambient water-table, although the large catchment uphill to the west cannot be ignored and adds greatly to the turbidity, due to run-off, in times of heavy rainfall. This theory which could be investigated by digging a few test holes in the vicinity, to see if they fill, and checking the levels against the pond over a period of a year or so.

IT MUST BE REMEMBERED THAT I COULD WELL BE WRONG. GREAT CARE SHOULD BE TAKEN WHEN UNDERTAKING ANY FUTURE DREDGING, OR DEEPENING, SO AS NOT TO RUPTURE ANY CLAY LINER THAT MAY BE PRESENT.

The sunken aspect of the pond does it no great favours ecologically, as it shelters the surface from disturbance by the wind ensuring that oxygen levels remain lower than might otherwise be the case, especially when the aquatic flora is in poor shape.

Highslide JS
The Overflow - the removal of 4 bricks from the top of the structure would provide the simplest, most foolproof, solution...
The Overflow...

It has been mentioned that in times of extreme rainfall the water level rises to flood over the island. I understand that this is a fairly rare occurrence and one which could be rectified, most simply, by removing several courses of bricks from the top of the enclosure surrounding the out-fall pipe. A conventional sluice, using stop logs, would, I fear, prove too much of a temptation to vandals, which would be extremely difficult to protect. In any case I feel that this, or other methods of providing variable level options, would be an unnecessary complication and suggest that the removal of 4 bricks from the top of the structure (with the level at a fraction over three bricks from the top the water is just lapping at the bottom of the duck-house steps, so four bricks seems to be about right) would provide the simplest, most foolproof, solution, given that the protective grid is retained.

By the time I first became involved with the site, in the early nineties, the pond was in a sorry state, having reverted almost to dry land on the eastern side, with very little open water, which was choked with bur-reed and reedmace on the western side. Substantial dredging of the western side in the winter of 1993 and the eastern side the following year restored the situation, although, while the western side was dug out as a gently sloping dish shape to a depth of around four feet, the eastern side was only profiled to a depth of around eighteen inches, perhaps because of root obstruction from the trees bordering the pond at that end. Other than the potential to silt up again rather quickly this shallowness was, in itself, not a problem as a range of depths can only be beneficial, particularly to the invertebrate population.

Following the structural works the pond was replanted with a variety of oxygenating plants and a wide selection of marginals. I also drew up an extensive management plan for the site, which included the neighbouring trees and grassland bordering the pond. Over the next three or four years the wildlife flourished, with both common and great crested newts, frogs, dragonflies and all manner of invertebrates being present, and easily observable, in substantial numbers.

Highslide JS
The Duck-house - with the level at a fraction over three bricks from the top the water is just lapping at the bottom of the duck-house steps...
The Duck-house...

It has come as somewhat of a shock to see how badly things have deteriorated over the intervening period. The area of open water remains greatly improved, and has held up well, at least until late summer, when, over the last two years of protracted drought, it has become dangerously depleted, presumably due to a fall in the local water table, which is beyond our control. It is, of course, possible that the pond is of a puddled clay construction, fed solely by run-off, and the liner has 'coincidentally' failed over the last few years, but I think this unlikely. Hopefully this will not become the norm and levels will return to a healthier level in future years. The water quality, however, has declined dramatically, as has both the aquatic and terrestrial flora. Some work has obviously been carried out on the trees bordering the pond at the eastern end but the grassy border has been cut hard back, down to the water level in parts, and there has been considerable dumping of rubbish and vandalism of the once splendid interpretative boards (one of which has been salvaged and refurbished).

There was, I am told, a major problem with extensive duckweed cover and algal growth during 2005 (both symptoms of enrichment) which, together with tree shading, exacerbated the problem of light exclusion from the once fairly clear depths. This has resulted in the loss of submerged oxygenating plants, which have also been adversely affected by grazing from an excessive number of waterfowl (mainly mallard) and smothering with rotting leaves (a major source of enrichment).

On the subject of signs, in these days of manic litigation, I notice that The Town Council have, thus far, refrained from erecting any "Deep Water Hazard" warnings and wonder if they have considered the implications of this within their risk assessment of the area, in an age when it seems we need to be told not to step off of cliffs for fear of falling, or to avoid touching high voltage power lines due to the risk of electrocution?

Ultimately a choice must be made, for the future, between a wildlife haven and an attractive duck-pond, which is a perfectly valid option given the location, and one, which requires little change in management to promote. This would in all probability be the preference of the majority of the local population, however, having established that great crested newts are still present we have certain responsibilities for their welfare and some fairly dramatic changes may be necessary if their survival at Stangrove Park is to be ensured.