For the Hydrological Impact Assessment of All Land Development Projects

The frequent periods of heavy rainfalls that have followed the December General Elections, coming after the pre-electoral periods of lack of rainfal, have brought into focus the inconveniences of either too much or too little rainfall. To most people no rain means no water in the tap and too much rain means floods, landslides, and other inconveniences, including no water in the tap as the citizens of Port-Louis know too well; they are then told that because of the heavy rain the river water has become muddy and cannot be allowed to go through the filter beds. We put all the blame on the rain and accept all the inconveniences as a fatality ; we are not told that floods and landslides are the results of the interaction between land and water and that although we cannot control rain, the nature of the land on which the rain  falls is very much affected by human  activities. It is important that we understand the interaction between land and water so that we can be aware of how our actions can result in inconvenient or even disastrous events. The study of the movement of water on land is called  hydrology ; let us see briefly some basic hydrological processes that take place when rain falls.
Everyone can see that when rain falls on an impermeable surface like asphalt or concrete very little is absorbed, most of it collects on the surface and eventually runs down the surface following the inclination; this phenomenon is, quite logically, called surface run-off. On the other hand when rain falls on a surface covered with vegetation, for example a lawn, the water will not immediately run off the surface but will be absorbed by the soil. This is because the roots of the grass dig small holes in the soil and the rain water penetrates the small channels that are thus created and get absorbed by the soil. If the amount of rain that falls is less than the absorption capacity of the soil, all the water may be completely absorbed by the soil, without causing any surface run-off. If more rain falls the water penetrates further and further and saturates successive soil layers until it reaches a layer that is impermeable and starts accumulating and becomes what we call underground water. The permeable soil layer that is found on an impermeable layer and can retain water or allow it to flow through is called an aquifer. If we dig a hole into the aquifer at the spot where the water has accumulated we can tap into this reservoir and draw water manually as in a well or use a pump and obtain water for our use. Mauritius being of volcanic origin, there are lots of lava flows with plenty of empty spaces into which water can collect or flow. These constitute a distribution system for rain water from the wet Central Plateau to the drier coastal Regions. We are lucky in Mauritius that the water from underground sources is of good quality and needs little or no filtering. Further these natural underground reservoirs are gifts of nature and cost nothing. More than 50% of our domestic water comes from underground sources.
The perenniality of rivers, lakes and other sources of water
Let us go back to the upper soil layers to find out what happens to the water that has accumulated there; they perform important functions too. The top soil layers supply water to scrubs and small plants for some time after rain has stopped falling. The lower layers act as a sponge: they store water and slowly release it afterwards into natural drains, rivers and lakes for a long time after the rain has stopped. This capacity of soil to absorb water and release it slowly afterwards ensures the perenniality of rivers, lakes and other sources of water.
This brief description of the basic hydrological processes should make it clear that we should not interfere with natural processes without having carefully studied the consequences. Let us look at what the consequences will be if, for example, we replace natural vegetation by concrete, asphalt or bare soil. I must point out here that bare soil is almost as bad, if not worse than concrete or asphalt, as far as its interaction with water is concerned. When rain falls on bare soil there occurs the phenomenon of pounding; the rain drops beat the earth and convert it into thick mud that blocks all the pores in the soil making it impermeable. There is then increased surface run-off, but this water is full of mud resulting in silting in reservoirs and blocked filters for run-of-the–river water supply systems like that of Port –Louis. Thus replacing natural vegetation by concrete, asphalt or bare soil will result in increased surface run-off. If we do that on a large scale any moderate rainfall will result in considerable surface run–off with large amounts of water flowing downhill and collecting in drains, rivers, streets, yards, houses, tunnels, in fact, in any space that is in its path, unless necessary precautions have been taken. The frequent floods that we have witnessed in recent years are a direct consequence of the reckless way in which we have been carrying out our so called “land development” which in reality should have been called “land destruction”.  Another consequence is that since concrete, asphalt or bare soil do not allow water to percolate into the soil there will be less ground and underground water recharge and consequently less water in the aquifers for our use. So the overall consequence of our present land development policy in more floods, less ground and underground water, less water in lakes and reservoirs in periods of low rainfall, with all the hardships that all these things mean to the population.
We should not construct on sloping land without a proper geological study
Another phenomenon which has become more common in recent years is landslides following heavy rainfall. This happens on hills, mountain slopes and other sloping terrains on which heavy buildings have been constructed. As its name implies it is the sliding of land over the impermeable layer which has become slippery because of the water that has collected there. If the pressure is too much because of the weight of the buildings the land sitting on the impermeable layer will slide down the slope and we have a landslide. The moral of the story is that we should not construct on sloping land without a proper geological study.  
There is no doubt that a lot of recent developments have been reckless, careless, more motivated by greed and very short-term economic gains than the long term common good. It is obvious that we cannot keep going at this pace any longer. While we are not advocating the stopping of all land development projects we strongly feel that there should be a reassessment of their real benefits to the economic and social life of the population.   In any case as the above short description of the hydrological processes has made clear, it is necessary to have a Hydrological Impact  Assessment of all construction projects big or small , including  individual houses, before construction starts. Further, it has become imperative that we have a proper Land Use Planning, or Spatial Planning. The number of Town and Country Planners is a sad indication of the importance we attach to this important function; I believe that at the moment the country can boast of having around fifteen planners; Singapore has around three hundred!
Smart cities and Technopolies
The new budget has proposed the construction of 8 Smart Cities and 5 Technopolies.  I would strongly recommend that none of these projects should start before  proper Hydrological Impact Assessments have been carried out. There should be no exception to the rule: all construction projects must go through the process.  What I am proposing may seem rather severe , but we have no choice if we want to avoid more and more disastrous floods every year and more severe water shortages. The angry reactions of the people to such occurrences should make it clear that failure to act now may be very costly in social terms and in the necessary technical corrective measures that will have to be taken. If all the construction projects that are being envisaged at present are allowed to go ahead we shall cause irreparable damage to the environment, specially to our land and water resources, and future generations will blame us for our greed and lack of foresight.