(20 November 1978)
A visit was paid to the Port Dickson area to inspect beaches and demonstrate the use of SWS system in the sea. The Unit was successfully installed in a tidal pool. The site had much more fine sand than was ideal but the bed was graded up by introducing five buckets full of coarser sand collected from the upper beach. Development was proceeding well after a series of stop/starts, one pumping back and one release of suction, but the pump was running poorly which resulted in slow progress. Long before development was complete, it was time to leave the beach, but the sequence had been shown clearly and understood.
The beaches in this area vary widely even within a distance of a few metres. The stratification also was very erratic: frequently the fine surface was only a few cm deep and underlain by a uniform brown layer of coarse sand. This pattern was usually repeated several times up to a depth of c. 40 cm. In such beaches, very careful preliminary survey is needed to select the optimum spot.
In the morning of 21 November, a Unit was installed in the shallow margin of a disused tin dredging pit. The coarse sand includes much clay, well distributed and free, but there are a few pockets of solid grey clay. The water over the Unit was muddy and turbid but after c. 1 hour pumping, the filtrate had only a bare trace of milkiness. The quality continued to improve and this trace of opalescence would probably be lost. On such a site, full development would take the greater part of a day and careful selection of site is necessary to ensure full depth of sand and avoid large lumps of clay which would continue to colour the water for some time.
The object of this exercise was two-fold:
To give the fisheries officers experience of in situ working in easy conditions.
To evaluate the sand/gravel tailings on old tin mining sites as a potential medium for artificial filters.
In the afternoon, a visit was paid to a group of Government fish farms northeast of Kuala Lumpur. It was planned to establish an artificial bed in one of the ponds, but instructions had not got through in time for sand to be delivered. It was, therefore, decided to run a trial in the river flowing alongside the complex of ponds and supplying them with water. This river is fast-flowing, heavily coloured, with a bed of deep coarse sand. The most easily available reach was selected for reasons of convenience, for work began only at three o'clock. The Unit was established below a large granite outcrop which gave it protection from the stream. After thirty minutes' pumping, the filtered water was markedly cleaner than the raw water and it continued to improve: progress was again hindered by pump motor trouble, for this surged continuously and would not stabilise at the flow required.
Two days are insufficient to allow more than a brief comment confined to the area actually seen, but the topography and geology of West Malaysia are such that these remarks are probably applicable much more widely. From beyond Port Dickson to some 50 kilometers northeast of Kuala Lumpur, i.e. the area visited, coarse sand is available in almost unlimited quantities - in old tin workings, in massive dumps dredged from the rivers to reduce the danger of flooding, in the river beds themselves (the source of much industrial aggregate) and also on certain beaches. Some of these have a clay content which should be washed out before actual use, but the existence of such deposits should make the construction of artificial beds in fish farms, etc. both cheap and simple. (See Appendix 8.)
Most of this sand is of granitic or similar origin; the quartz makes an excellent medium but the decomposed felspar breaks down into the clay that colours many rivers permanently and although most of this is taken out by the SWS system, it is likely to include some very fine particle that may remain to give a faint opalescence.
Some waters are too fast-flowing to provide ideal in situ beds, but few stretches are wholly uniform and careful survey is likely to locate slower and more suitable sections. Where only fast water is available, the Unit should be placed as deep as possible and the line thoroughly buried to avoid dangerous scour, but the formations of a fine surface layer is impeded by the constant “rolling” erosion, in which the surface layer, while running at the same stable level, is constantly being renewed. However, the one trial run in such a river showed that successful working is possible.
Comparatively few parts of the west coast are suitable for the direct abstraction of clean water, one of the exceptions being the area around Port Dickson, where some sections of beach appear excellent. Here, again, careful survey will show some patches as being very much more favourable than others. Attention is drawn to Appendix 6 on the abstraction of sea water by stainless steel screen wells. Alluvial sands are known to underlie many swamp and mud zones at various depths, and if clean sea water is needed, for either laboratory work general cleaning purposes or for fish farms, brief exploration to a depth of several metres by the method outlined there is worth considering.
