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Urban Salinity and damage of buildings

Salinity can be controlled and lands reclaimed, though not overnight and not easily or inexpensively

By Dr. S.M. Alam NIA
Tando Jam
Dec 10 - 16 , 2001

Salinity has long been recognized as a major problem in rural areas for agriculture and damaging of buildings, in urban areas. However, it also affects deterioration of towns and cities across the country. Evidence of salinity can sometimes be seen in damaging building's foundation and roads, but damaged foundations and underground services may be more difficult to detect. Urban salinity, like salinity in rural areas, is caused mainly by rising water tables, through excess and frequent watering and infiltration from rain, bringing salts to surface, causing salinity and water logging problems. Historically, the salinity has damaged or destroyed many civilizations in the past. Water is the upper surface of groundwater, below which the layers of rock, sand and gravel are saturated with water. In a well-balanced system, the water table usually remains many meters (1 meter = 3.28 feet) below the Earth's surface. Any amount of water added to the garden, in excess of evaporation and plant needs, filters down slowly through the soil, thus adding to the groundwater and making the water table rise or high near to the surface. A water table rising towards the surface, carries with it dissolved salts that are normally locked in the soil and rock profile.

The problem of salt in agriculture is not new, or limited to the worldwide. FAO experts have estimated that salinity affects productivity on about 80 million hectares or arable land just about the total land area of a country like the size of Pakistan. The problem arises, when salt is left behind in the soil as water passes back into the atmosphere through the processes of evaporation and plant transpiration. In areas, with good rainfall and effective drainage systems, the soluble salts change in composition and concentration as water carries them away, eventually to the seas. But, in parts of the world having little rainfall and restricted drainage, the salts can not easily be transported. They accumulate in lowlands or in the groundwater below them. Natures own geographical and geological processes are major contributors to salinity. Experts say that more than 30 million hectares of salt-affected land arise from natural causes, aridity, and high rates of phenomenal evaporation of water from the soil surface.

More saline lands are in or near areas, where irrigation is the backbone of farming, predominantly in developing countries. Lack of good drainage is a major contributor to salinity. So is seepage from irrigation systems and drainage fields, which can lead to a loss of nearly half of the water. Gradually, the groundwater table rises bringing salts to soil layers, where crops get nutrients. As surface water evaporates, the fields become white encrusted, salt-capped wastelands. Farmers abandon them and agricultural economies suffer. Salinity can be controlled and lands reclaimed, though not overnight and not easily or inexpensively. One approach is constructing good irrigation systems that gradually improve soil conditions and prevent formation of water logged and unproductive fields. Unfortunately, poor irrigation practices often promote rather than control salinity and engineered drainage systems extending over large areas of and are financially out of reach for most countries. Biosaline agriculture suiting salt-tolerant plants to soil and water conditions may offer more affordable alternative, though not necessarily an easier one.

These salts such as NaCl, Na2SO4, Na2CO3, CaSO4, CaCl2, Ca(NO3)2, MgSO4, MgCl2, Mg(NO3)2, CaC03, etc. generally accumulate at the surface, causing salinity problems in and around the locations or on the spots. Other factors contribute to a rising water table along with excess garden watering are: tree clearing or cutting in urban areas, over-irrigation of public recreation areas, disruption of natural drainage lines and over flow of septic tanks and sullage pits. The effect of salinity on the environmental material is very serious. Saline ground water kills grass, shrubs and trees, damages roads and buildings, corrodes pipes, causes water logging, scalds ground, destroys soil structure and damages septic tanks, cemeteries, rubbish dumps and water supplies, lawns and shallowrooted, so can utilize little water. Most water applied to lawn drains through beyond their root systems.

Urban salinity is a complex process affected by characteristics of the local and regional geology, so evidence of salinity, and the damage it causes, may not occur throughout the whole urban area and may take many years to become apparent. Even though a house or a street may not feel the direct effects, poor water management may aggravate the problem elsewhere. That is why, dealing with the problem requires a committed and coordinated approach from government and the community. The cost to the community is enormous. For example, the reconstruction of just one street block of a roadway cost an enormous amount. Similarly, the repairing the foundation of a house or rebricking the lower course can cost substantial amount. The major effects, which can be seen on the items of the locality are as: Unhealthy or dead grass, shrubs and trees; greasy, boggy or water logged ground; spread of salt tolerant species such as couch grass; bare patches of ground, often with white crust on the surface; septic tanks not working properly; deterioration and rising damp in bricks and mortar; white crust of salt on brickwork, usually close to the ground; cracked or collapsed pavements, roads and driveways; shifting or sinking house foundations; corrosion of water, gas and sewage pipes.

One should follow the following instructions as precautionary measures: Avoid water wastage; don't over-water lawns and gardens. Lawns are shallow-rooted so don't utilize much soil water. Most water applied to lawns drains through beyond the reach of their roots; group plants with similar water needs together and gives water only, when there is almost necessary; plant deep-rooted plant varieties and have small lawn areas; use mulch on garden beds;' keep plants healthy by testing the pH value of the soil. Lime or fertilize as appropriate; don't wash your car on the lawn unless the ground is very dry; don't empty pool water onto the lawn; connect roof drainage to the storage water system, not to sullage pits; join or start a local urban land-care group.

Salt action is a strategy for joint action by the government official and the community. Its aim is to manage and control salinity levels within the land and water resources of the State as an important part of Total Catchment Management. Salt action recognizes that people are the key to tackling the State's urban salinity problems.

Individual residents, community groups and governments all have an important role to play. Researchers are currently documenting the complex processes involved in urban salinity: the movement and characteristics of ground water, and regional or local geology, climate and land use. Community involvement is essential to assist in the collection of data and to ensure that urban salinity is given the attention it deserves.