Cleaning Of The City Rivers

CLEANING CITY STREAMS: PUTTING HARVESTED RAIN WATER TO WORK. PROF. THRIVIKRAMJI.K.P FORMERLY OF DEPT. OF GEOLOGY, UNIVERSITY OF KERALA, KARIAVATTOM CAMPUS [email protected] INTRODUCTION Yet, with a steep rise in the population since independence, the need for a better quality of life, domestic water needs of Kerala increased several fold. This and the growth of urbanization naturally affected a blow to the natural drainage net in cities. Take for example Trivandrum, once (in my school days) very attractive town, with several ridges and valleys, and skirted by the coastal land along the western edge, ensuring quick escape of monsoon run off chiefly in the Karamana Ar., Killi Ar. and the Amayizhanchan Thodu, Kannanmoola thodu and Ullor thodu. Despite this, there was a guaranteed base flow out side of the monsoon seasons, which maintained unhindered flow in the channels freeing the channel of the solids and waste water of a totally different complexion compared to its modern analogue. Regrettably, these days these streams no longer efficiently remove the new generation waste (whether solid or liquid) intentionally and carelessly jettisoned into stream channels especially outside the monsoon fed days. One can site several reasons for such inefficiency. During the dry days, which are nearly 173 or so in a calendar year, the flow in these watercourses is either nearly sluggish or absent or even stagnant at times, resulting in ever rising accumulation of biodegradable and other types waste as well as wastewater from domestic and some non-domestic sources. This state of the city stream net work at times poses a great health hazard for the citizens who traditionally had and continue to depend on its waters. In what follows, I will elaborate upon the present state of these streams and will propose with reasons the application of Modified Rainwater Harvesting (MRH) to force clarify the water carried by the streams in the summer months. Morphology of Land area A primer on the landscape and its foundations will be useful for a better appreciation of my theme and arguments. The Greater Trivandrum Region (GTR) is covered by a surface or ground (= morphological features) of shallow and deep furrows (valleys) now occupied by streams of different sizes separated by ridges (= continuous and long ridges). For e.g., the Ulloor-Kannanmoola road and the Kawadiar Thycaud road are aligned on or along the sides of ridges, and which are separated by valleys now ex-paddy fields or stream courses. Though many of the ridges hover in the elevation range of range of 30 to 50 m, the elevations of both the ridge tops and valley floors tend to rise toward east. The streams tend to follow the orientation of the furrow system, until these reach the plains of Manacaud and Kadagompally and further west and north. The nature of surface morphology of Trivandrum is largely influenced by the structure and nature of the rocks and sediments that cover the ground. Geologically, basement is composed of the crystalline rocks or Karimkallu (gneiss = the usual light colored rock used as road metal and in the foundation-basement of modern buildings and charnockite = the dark colored rock which is a.k.a. Kovalam kallu ). Exposures of these rocks occur at Parakovil; Aduppukootan para of Peroorkada and to the eastern side of Trivandrum Kovalam Road beyond Pachalloor as well as at Kovalam along side the Hotel Complexes. In sectors where Karumkallu is unexposed, the ground cover is Laterite (Vettukallu) or soil derived from it. The low lying plain and dominantly sandy tracts of Manakkad, Eastfort, Vanchiyoor, Pettah, Kadakampally etc are representative of the coastal land of Kerala (El.=<7.5 m.) In fact the ridges fall in the midland region (El.=7.5 -75.0 m). Chief drainage paths The major streams and rivers crossing through and draining the town are the Karamana Ar. and Killi Ar. and the Amayizhanchan thodu and Plamoodu thodu (which join to form the Kannamoola thodu) and the Ulloor thodu. The latter empties into the Veli Kayal where as the former merge and joins the Arabian Sea at Poonthura, north of Kovalam. The smaller streams or the thodus are now ephemeral and pools of a cocktail of solid and liquid filth originating from the cityscape where as the perennial Karamana Ar. and Killi Ar. rising in the Western Ghats and Midlands respectively pass through the cityscape receiving the discharge from the roadside gutters, wrongly released domestic waste discharges and seasonal overland flow from the adjacent land. Generalities of river flow Some general points of river hydrology are essential to better appreciate my model. Like other rivers of Kerala, these urban streams are also rain fed and receive their quota of water (whether bankful or flood) flow from the SW and NE monsoons and the base flow of summer season from the ground water stored in the aquifer rocks exposed on the channel walls. Unlike the surface water in the streams, the

velocity of ground water flow is extremely low ( and laminar), and hence takes a considerably long time before it emerges as springs or in the river channels to maintain a discharge (a.k.a. base flow) beyond the rainy days. According an estimate of IMD, Kerala enjoys at least 175 days of precipitation in the form of rain. Contrary to the highly paved, built up and covered ground of the cityscape, any virgin or unurbanized terrain offers and abundantly promotes recharge of rain water into the ground below to augment the subsurface reservoirs or aquifers. This water will be released through springs to feed stream net in the form of base flow. Any river cross section is a handy work of river to accommodate the flow through it that carries the bedload, suspended load and dissolved load of the stream efficiently. Problems with Urban streams In general, urban streams face severe hydrological and environmental problems. Urbanized regions are very large singular sources of man made domestic and industrial liquid and solid wastes (biodegradable and non- biodegradable). Even with greatest care, it is quite difficult to prevent dumping or release of such waste into the stream channels. No law or prohibitory decree is of any use. Instead, putting in place of a waste disposal system of appropriate capacity is a better solution. The costs are obviously very tall compared to the ability of the city government to pay for it. The solid waste dumped into the channel adds sharply to the higher bedload, often way above its capacity. Then channel parameters (like cross sectional area, depth and width) and discharge at such points is not in tune with each other. Consequently, channel bed rises in elevation leading to a fall in the area of cross-section and results in blocking of through flow in summer and floods in monsoon. Urban liquid waste The liquid effluent entering the streams is far from clean and instead it s a cocktail of residues of domestic chemicals based detergents, residue of paints and other chemicals from rejected tins and cans, left over soft drinks and bottles, unused medicines and some times even pesticides as well as liquid waste originating from small scale production units. This dose of waste water into the streams spoils the stream water that is already loaded with urban solid waste. Reduced recharge Further, the urban sprawl of road pavements, paved side walks, paved and walled roadside drains, large and small buildings (of commercial, residential and service sectors), their paved environs, have tremendously curtailed the rain water seepage in to the ground to ultimately recharge the aquifer rocks of subsurface. The immediate consequence of this phenomenon manifests as higher stage heights in the streams, as well as a reduction of duration and volume of base-flow in the city streams and especially in the drier summer days. The low base flow quickly hinders the river flow and consequently leaves the channels un-flushed and covered with pools of filthy water separated by exposed river bed or riffles.

The ever growing expanse of paved areas and newer buildings, increasingly intercept the rain water of the urban tract and redirects into the storm drains or paved street side gutters finally to empty into the city s natural drainage channels, resulting in a sharp reduction or near total loss opportunities for free percolation of rain water down the soil and hence toward the ground water (GW) aquifer. Consequently, the GW aquifer will not be in a position to support the streams to maintain a base flow through the dry seasons or summer months. This phenomenon too transforms the city streams into a filthy pool of untouchable and disjointed but stagnant pools of water. In fact, the slogan that dilution is the solution to pollution is forced to the backbench. Yet, the natural cleansing of urban stream segments will take place in our climatic zone only twice every year during the SW and NE monsoons. Due to the shortened duration of base flow, for the rest of the time the streams and their water present an ugly look themselves. Indeed, I strongly believe that the use of a technology described in the following will regenerate and rejuvenate the base flow, its extent and volume, so that the streams will be reborn with a capacity to self clean the channels clogged with dirty looking concoction of urban liquid waste by simply diluting it and re-establishing the flow. The New Technology Harvested-Rain-Water is the work horse of the new technology to induce and rejuvenate the self cleaning potential of streams. Fellow citizens in other parts of India have either known it long ago or have been practicing since the historical time, especially in traditionally rain scarce regions. And near home, the Chennaites have been successfully practicing it for the last several decades. In the original format, it is called rain water harvesting. The CGWB (Central Ground Water Board) has identified this program as one of their priority missions. In a large country like India, it is usual to come across a variety of climatic zones (e.g.,

Rajasthan Desert, the Chirapunji tract of Assam and the Monsoon belt in the coastal areas of Peninsula). Logically, with the exception of the Gundu Is., this practice never preoccupied the minds of Keralites any way. The Gundu Is., of Vembanad lake just to the east of Vypeen, is a little known example in Kerala where roof top rain water is harvested and stored for later use. The rain water intercepted by the roof is guided through the roof edge gutters and then same is directed to huge light proof over the ground masonry storage tanks. The express use of this water was in preparing dyes for use with the coir fiber. By the way it was an expatriate Britons idea. This is not entirely what I propose in the following. I propose that harvested roof top water from the homesteads located in the ridges or midland of urban Trivandrum (El.=7.5 -75.0 m), be used to recharge the aquifer rocks below the ground surface, following a simple modification of Gundu Is. practice. Firstly, vertical shaft of say 1.0 m. diameter (lined with cement slotted-concrete-rings of suitable size to cover the soil zone) be dug in every house hold either in the back or front yard or even inside of the garage, and be covered with a concrete slab having appropriately placed air vents. It is advisable to keep at least a depth of 4-5 m. The shaft needs a filter bed or layer (thickness =1.0. m.) of very coarse gravel (or a layer of 10 to 15 cm. size blocks of Karumkallu) followed by a layer of coarse sand separated by a nylon net to prevent seepage of sand into the interstitial spaces of gravel. It is advised to leave a free board of at least 2 meters, above the sand layer in the shaft. The water that drains the roof top can be directed into such shafts. In fact, such shafts can be constructed even in side the garages, if open space is at a premium in the compound. These recharge shafts will have a huge potential to add tremendous quantities of water to the aquifers. The advantages are several. Firstly, the water accumulating in side the house hold compounds do not freely flow off to the street and then to the street side gutter and finally to the stream channels only to raise the water level to alarming heights and instant flooding of low lying areas resulting in dislocation of city life, loss of materials and property. Secondly, with this system in place, the water that drains out of the homestead compounds into the streets only to over flow the clogged road side gutters and over the road pavement will soon become part of history. Further, accumulation or broadcast of solids and such other materials (on city pavements) that could harm unwary public will stand greatly eliminated. And finally, as the aquifer storages are augmented considerably by this recharge technology, followed by its slow release into the stream channels, the base flow regimen under goes strong rejuvenation and vitality. The express advantage of this paradigm change is increased flushing of the filthy residual pools of water in the channels an eye sore- and beyond the rain fed days. As a consequence, the dilution of the waters of the urban stream segments takes place and will result is in a better appearance of stagnant pools of urban cocktail in the streams. --------