Dying Rivers Of Kerala & Sand Mining: Dr.thrivikramji.k.p.

DYING RIVERS OF KERALA: CONSEQUENCE OF OPTIMAL RIVERSAND MINING My dear Reader Here are some of the points I do share with you against your question of where to mine the river sand. I have been accustomed to the use of sand borrowing instead of mining. Because it is not exactly any mining. Borrowing means there is an implication that you return it, but don t know when. Secondly, the lender also would need it in the long run. Wherein from the river channel? The best answer is from the flood plain as well as from the channel. The flood plains as a freehold land are no longer available. It is either undergone tremendous changes or simply not available. From a farmland status it would become a residential community by the fast changing land use practices. Now we are left with the modern channels only. For all practical purposes the channels relatively narrow, and like any other channel it swings to both sides as it propels down stream. There are very few sites of any reasonable extent with a straight channel. In a channel the sediment is supplied by the sub basins that supplies water. The depth of weathering, nature of rain fall, rate of erosion and nature of slope will decide the quantum of sediment coming off. In a catchment or basin exposing only hard non erodible rock practically load of any type is supplied. But the erosivity of the flow will not easily diminish. The kinetic energy is what is critical. In a solid only cover, the sediment supplied will be proportionate t o the area, intensity of rain fall, the nature of slope and depth of weathering. Box.1. A sample estimate of Sand content in the source rock We all know that only 27% is the av. content of quartz in the rocks like charnockite and gneisses exposed in the land area of Kerala. Given a Sp.g. of 2.7 Quartz content in kilograms in one m3 of rock will be like Quartz = (!.0 m3 x 2.7)/0 .27 ton Or a cube of 1.0 m3 rock will weigh 2.7 tons 0r 2700 kg. Its quartz sand content = 2.7 ton x 0.27 Or 729 kg. not even one ton of sand. Look at the issue from a different angle. Take 1.0 km2, thick slab of rock of 2.0 mm. sp.g of 2.7 and quartz content of 27%. 0ne km2 of rock would cover an area = 1000 m x 1000m = 1,000,000 m2 If the rock has 27% quartz, then for a thickness of say 2.0 mm the quartz content will be some thing like this. = (1,000, 000 m2 x (2.00/1000 m) will be the volume of the slab of 1.0 km2. Then sand content is = (1,000,000 x 0.002) x 0.27 = 1458000 kg or 1458 ton of sand. Or @ 8 tons/truck, it will be only like 182.25 truck load or say it is only 180 truck loads . But what is the time span for releasing this volume of sand? If you allow 1.0 mm of denudation per say million years to produce this sand, then how much sand you really get from a river basin and that released over a 1,000,000 yr.. Now what comes to mind is the rate of weathering issue in the tropical climate. You know how it is determined or the difficulty of deciding it. But there are several indirect means of assessing the weathering rate using geological insights of chemical weathering process. . Or even allowing 1.0.cm of denudation per million years, you end up with 180 x 5 truck loads. Our friends in the CESS and CWRDM for their own reasons did not look at the sand yield from the point of view of denudation. So in a decade or two of their assessing the river sand yield at kadavus, all the rivers landed into their present status,

When the flow oscillates between the right bank and left bank in the channel, alternating side channel bars or point bars are built. The point bar- pool pair always occurs together. It is the pool that is with deeper water during the base flow and perhaps this section is made use of by people living in either shores of the river traditionally made use of for various purposes. The pool was the place where cattle were given a bath. People of the community also used the pool for bathing, washing clothes as well as lifting water for domestic use- especially women carried water in filled pots either on their head or in the waist securing the pot safely over the hipbone. Thus such section of a river in Kerala became a busy place that attracted local people for various reasons. And also became a river crossing point with or with out a ferry facility. Otherwise, there is scientific basis for the kadavus which are recommended for removal of measured quantities of sand based on the seal of approval either by CESS (in the southern rivers) or CWRDM (in the northern rivers). The entire state of Kerala (excluding the coastal land and high land) with its laterite cover the region that is the potential source of sand cannot yield all the sand we have so far used if you follow my model? This is my model of sand supply. In a river the channel is either straight or curving. In an alluvial channel volume of sand is very large compared to a rocky channel. The mid channel bars and side channel bars are largest san reservoirs in the channel. I would suggest that a portion of this sand is removable, provided you know what the sand discharge is?. Which is equivalent of the sand supplied from the river basin? There are paleochannels, and once upon a time the venerated GSI had plan for mapping the paleochannels for future removal of sand. In fact the paleochannels are the paddy fields in Kerala. These valleys do have some sheet or ribbon sand. More likely the ribbon sand. I always voted for crusher sand or manufactured sand. It is used by the multistory structure builder all over Kerala as sand in Kerala became very scarce. The columns beams and floors are made of concrete and the brick is hollow brick or manufactured brick. It is good for top soil. Most of the time top layer of clayey soil in a paddy field is used for making red bricks. The hollow brick saved the paddy and other farmlands. The sand or fine aggregate as it is called in the industry circles is manufactured by crushing and milling blocks of rock. The govt did not ask the industry to go for it. When they wanted to maintain the profit margins automatically went for the crusher sand. Entry of manufactured sand has helped the rivers a great deal in their march to natural state. While the rock is crushed you make coarse aggregate (metal for road railway ballast as well as foe concrete). Of course the metal is manufactured in different grades to suit the various end uses. The process also creates fine aggregate equivalent- of construction sand as well as finer materials. The finer materials do not fine favour in any sector of the construction industry. Even allowing a 15 0r 20 % of waste, it is always a greatly profitable pursuit as most of the input is converted into useable end products. In the natural process of weathering from any unit volume of rock only say 1/3 is available as sand and after natural process washing and grading, the ultimate product will be even ¼ the size of the input in the natural weathering process. Secondly the time required for the natural conversion of the rock to soil and liberation of sand grains to be at the disposal of running water takes a million years or so. As a consequence, the demand side for natural sand may be on the rise. But supply side is stationary and unchanging. So I will not recommend use to natural sand from the rivers oif Kerala, instead my suggestion is use of manufactured sand. Flue gas or fly ash is mineral matter originally occurred in the coal. It is is now in the state of glass non crystalline. And is generally of the granularity of sand. So it qualifies easily as fine aggregate. In Kerala itself, the Vellur News Print Factory produces large volumes of fly ash during the operation. Large volumes of it are used for land filling in the wet lands on the left bank of Moovattupuzha river and to the west of the Tvm-Ekm rail road. A sizable quantity is consumed in the making of Pozzolana cement in the neighborhood factory. But as I said large volumes go into the landfill. The leachate from the fill certainly

pollutes the water of the Moovattupuzha River. Yet there is no concerted effort ot use the flyash as a substitute for fine aggregate in the construction sector. The sea sand is equally useful stuff in construction. By scientific screening suitable patches of sand can be located in the off shore Kerala and can be suction dredged without great harm to the ecology of coastal waters. Only thing is this sand needs washing and cleaning before it is marketed. ----------------------- .

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