June 6, 2004

The entire ecosystem of Manchar Lake has been severely disturbed by effluents

Manchar Lake is a large, shallow, freshwater body formed by natural depression. It is flanked by the Indus to the east, the Laki Hills in the south and Khirthar Hills in the west. It is situated at a distance of about 18km west of Sehwan. The northern and northeastern boundaries are formed by flood protection bunds as the lake is spread over an area of about 246 square km.

In the past, when the water quality of the Lake was acceptable, Manchar used to provide support for the economic activity of the people living in the area. It provided livelihood for fishermen, water for irrigation, including cultivation of lotus, tourism, water for domestic use and breeding grounds for migratory birds.

However, over the years the quality of water has deteriorated and environmental deterioration of the Lake has continued as a result of human-induced interventions. These include construction of Aral channels for linking the river to the lake construction of flood bunds and construction of Matti Nara Valley Drain (MNVD) that have brought saline effluents into the lake.

Over the years the storage capacity of the Lake has reduced significantly, due to sedimentation. It surface area, at water level of 35 meters, has reduced from 21,100 hectares in 1964 to 20,600 hectares in 1990. Likewise, the water storage capacity of the lake has reduced from 308 million cubic meters in 1964 to 202 million cubic meters in 1990. The relatively higher rate of sedimentation is indicative of not only high silt load and other settleable solids in the effluents discharged into the lake, but also, of poor lake management and negligible control over the Lake’s watershed.

Manchar Lake is facing a major problem of annual water deficit. Water inflows are less than the volume of water abstracted and lost through evaporation. Abstraction and water losses are estimated to be 260 million cubic meters, while inflows from three link canals is limited to an estimated 120 million cubic meters, resulting in an annual water deficit of 140 million cubic meters.

Manchar Lake receives water from hill torrents, MNVD and the three link canals from the Indus i.e., Danistar, Aral Manchar and Aral Laki. Runoff from hill torrents is erratic and not regular. MNVD is a drainage canal and currently it is discharging saline effluents in the lake. This has impacted the water quality of the Lake, increasing the Lake’s salinity. In addition, agrochemicals are also added through this source.

Manchar is used for many purposes, including agriculture, fisheries and domestic water supply. Lake water is diverted through small canals for irrigation. These have been constructed such that they take off from the Lake. Water is pumped from the small canals for irrigation.

Fishing used to be an important economic activity for the people living in the adjoining areas. However, due to the deteriorating water quality and increased salinity, the fish yield has declined significantly over the years. In 1950, the fish catch was reported to be 3,000 tons/year. This reduced to 300 ton/year in the mid-Nineties. Presently, the fish catch is few tons a year. The colour of fish is also black and the quality is poor. Most fishermen have migrated elsewhere, to meet their economic needs.

Manchar Lake is a significant water body of Sindh. It has a high ecological significance. It used to meet variable requirements, ranging from drinking water and domestic use to agriculture and fisheries. It is also an important wetland site of international significance.

The main water quality problems of Manchar Lake are eutrophication (excessive weed growth due to nutrient enrichment), salinity, physical constituents and chemical pollution. Other physical and hydrological problems include sedimentation, water inflows and outflows (quantity and quality) and the retention time in the lake. The inflows to, and outflows from, the lake need to be controlled not only in terms of volumetric capacity, but also, in case of inflows, the quality as well. This is crucial for the Lake’s rehabilitation.

Conflicting uses of Lake is an aspect that would be problematic in lake rehabilitation. For example, in case of drinking-water, the parameters of concern are the fecal coliforms, total coliforms, turbidity, odour, salinity and presence of heavy metals.

In case of agricultural uses, the parameters of concern are sodium adsorption ratio and total dissolved solids (electrical conductivity). For fisheries, the parameters of concern are salinity.

Taking just one parameter into consideration, in the past salinity of the Lake’s water varied from 500 to 4,000 ppm (pails per million). According to WHO standards, the desirable maximum level of salinity in drinking-water is 500ppm. The absolute maximum acceptable level is 1,500ppm. For agriculture, the salinity level can be extended upto 2,000ppm. Fisheries requirement varies with the nature of fish. Typically, the value in freshwater should not exceed 1,000ppm.

While rehabilitation and improvement in Lake water quality should be the principal goal, as an interim measure, efforts should also be made to make most of the present saline water of the Lake. In a way, saline lake has its value, and the values can be used to the advantage of people living in its vicinity. Intention is make use of the present condition of lake, rather than leaving it discarded and classifying it as an environmental blunder.

Even the Ramsar Convention, signed in 1971, gives credence and support to the importance of saline water bodies. This would call for rational management of saline lakes, so as to make the beneficial use of the lake. Towards this end (management of saline water bodies), that is an interim measure, till the water quality is improved, some remedial measures, general in nature, could be suggested.

It is essential that the water quality degradation of the lake is stopped and its environmental abuse put to an end. Wide-ranging measures should be adopted to rehabilitate the Manchar Lake. These should include physical aspects, while the other should pertain to chemical, biological and hydrological aspects.

The first and foremost measure for the rehabilitation of the Lake is to stop the flow of drainage effluents into the Lake. No matter how costly measures are adopted for water quality improvement, no positive gains would be achieved as long as the inflow of drainage effluents continues.

The most efficient and relatively cost-efficient measure of rehabilitation of the Lake, is to supply freshwater from the river. Since at times, the water level in the river may be low, which may prevent the gravity flow of water from the river to the Lake, it would be prudent to install pumps, so as to pump the water into the Lake.

Filling of the Lake from the river and subsequent release of water would help in the control of Lake water salinity. In fact, this is considered as a major, cost effective step of controlling the salinity levels in the Manchar Lake. If freshwater inflows in the Lake are increased, this would have additional advantage in the improvement of water quality. This can be achieved by enlarging the channels linking the Lake with the river. Pumping stations are another source that can be used to increase the inflow of freshwater.

Control over the Lake’s watershed in terms of minimizing use of fertilizers and agrochemicals would be essential to reduce inputs of pollutants.

All municipal and industrial effluents must be treated and discharged elsewhere. They should not be in the lake. The Lake should have a clearly specified management plan, to ensure its water quality protection. The management plan should be implemented by a separate Manchar Lake water pollution control board.