Urban Flood Management – A Case Study of Chennai City

In the recent decades, Indian cit ies are witnessing devastating floods more often due to heavy rainfall, cyclones, etc., Though Tamil Nadu is not under flood risk p rone zone as mapped by meteorological department (New Delh i), within the local body there are few low-lying areas which are susceptible to inundation which also depends mainly on the developments near major drainage systems, encroachment of water bodies, inability of major canals to carry heavy rains, overflowing reservoirs. Chennai, one of the fast growing metros is likely affected by the lack o f drainage mainly due to uncontrolled developments of concrete spaces, encroachment of major drainage channels, shrinking of marshlands, etc,. Though Urbanizat ion, the vital factor of response for the flood risks is coupled with the climatic variability and ecological imbalances. The paper discusses causative factors responsible for flood risks in Chennai, the immediate need for proper flood risk reduction and management strategies.


Prologue of Chennai
Chennai, State capital of Tamil Nadu lies in the Eastern Coast of South India where three watercourses meanders through it namely, Coou m River, Adyar River and Buckingham Canal. Chennai is the fourth largest Metropolitan in India having a total population of nearly 47 La khsi with a growth rate of 13% and density of 26903. Within a century, Chennai has grown 8 fold t imes in population ( Figure 1). City is drained by those 2 rivers in addition to many major & minor drainage channels through Buckingham Canal to Sea ( Figure 2). The city is also having more than 50 Temp le tanks in addition to natural water bodies to capture flood water and acts as ground water recharging wells.
Chennai also has Pallikaranai swamps, Madhavaram & Manali jheels, Adyar & Couu m Estuaries as a wetland sources apart from natural & man made waterbodies.

History of Chennai Floods
Chennai frequently experiences flooding due to heavy rain associated with depressions & cyclones. Of which few catastrophic floods during 1976,1985,1996,1998,2005,2008 and 2010 caused heavy damages. Now-a-days, unexpected holidays due to heavy downpour are quite common especially during October -December. In short, Chennai is not starving for rain; it is starving for water which is due to mis management of water storage. In 2010, Chennai received about 760mm rain fall only during October -December period. Recent highest rainfall in a day was 423 mm on 27. 10.2005. All these shows whether Chennai is prepared to drain this flash flood without having hindrances in their day -today life? Closing of schools due to flooding every year is common in many parts of Chennai. Since it is more frequent every year why effective management is not so happened? Where is the lacuna? This article is aimed to arrive out the gaps in resolving the persistent issue. Though the paper is majorly based on data from secondary sources, the data analysis & inferences out of that is purely arrived on the basis of current happenings. (Table 1) Chennai -is not an exceptional one fro m other metros which is suffering due to rapid u rbanizat ion. It is also contributing with the increase in floating population every year as it is a hub of all majo r economical activit ies.

Causes of Chennai Floods
The follo wing are the factors [1] which hamper the liv ing in Chennai due to floods though it can be categorized broadly under changes in climate & micro-regional environ mental factors. Each factor ( Table 1) is dealt in detail in the subsequent clauses.  Figure 3). The city gets most of its seasonal rainfall fro m the north-east monsoon winds during mid of October to mid of December. Cyclones in the Bay of Bengal also sometimes hit the city.

MRTS Stati on, Mandaveli
Chennai with the fast pace of developments has witnessed a steady deterioration and decrease in the nu mber of water bodies. It is estimated that more than half of the wetlands have been converted for other uses. Chennai had about 650 1 small and big water bodies in and around the city, but today the number has been reduced to less than 30. Ownership of water bodies is scattered among various government departments and is the root cause for lack of proper management. The Protection of Tanks and Eviction of Encroach ment Act, came into effect fro m October 2007. However, there has been lack of imp lementation of this law.
This 65-year o ld map ( Figure 4) shows the locations of several water bodies. The gray areas of the map represent eris, or small ponds. The gray water bodies are seasonal, in that they appear during the rainy seasons and remain dry during the rest of the year. When this map is co mpared with the recent one, it shows many of the water bodies have either shrunk or disappeared. According to records of the Water Resources Department (WRD), the area of 19 major lakes has been shrunk fro m a total of 1,130 hectares to nearly 645 hectares and hence reduced their storage capacity. Also, the ground water level came down up to 10m within 5 years (1995 -2001) [6].
The drastic change in Land Use of Chennai [6] due to urbanization (1995 -2007) also adds fuel to the current risk 1Based on the research project done by Centre for Environmental and Water Resource Engineering, IIT Madras of flood in every year. The change in land cover during 1997 to 2001 is given in Figure 5. Most of the green cover are reduced to non-vegetative or a concrete space. Due to this, the surface run-off is too high and the infiltration capacity of land has gone down drastically. Due to the increase in impervious areas, Chennai experiences severity of floods during every heavy rainfall.  Many of the water bodies, green cover and natural depressions have disappeared due to the human induced successions as it is filled with wastes or developments/encroachments and become flood prone areas ( Figure 6) .

Topography
Chennai has a terrain slope varying from 1:5000 to 1: 10000. It is a low-lying area and almost like a pancake. It rises slightly as the distance from the sea-shore increases but the average elevation of the city is not more than 22' above MSL, wh ile most of the localities are just at sea-level and drainage in such areas remains a serious problem.

Inadequate and Poor Drainage Systems
Apart fro m plain terrain lacking natural g radient for free run-off, the sewage system was originally designed for about 6.5 lakhs population at 114 LPCD of water supply. Later it was modified during 1989-91 even then it has not reached the required capacity.
Due to du mping of garbage and massive reclamation, marshland especially in south Chennai ahs reduced to one-tenth of its size [12].
Also, the government has built a slum resettlement colony along the river channel and multi-storeyed housing estates have come up wh ich b locks the natural drainage o f river basin into the sea. The original silt ing pattern was shifted due to the development. Moreover, sewage and industrial effluent dumped into the canal and silt ing have left the waterway stagnant.
Planning of indiv idual div ision oriented projects without involving associated authorities is the major drawback which is reflecting as a major gap fro m the institution side. Absence of accurate topographic map is worsening the situation more.
Total waste water outfalls in water ways accounts to 85%. This is an alarming issue which has to be addressed immed iately.

Solid waste Disposal & Veh icle Parking on Roads
The highest per capita solid waste generation in India is in Chennai (0.6kg/day) 2 . Majority of solid wastes are dumped in a mixed form in low lying areas & in open areas by Chennai Corporation. The Attitude of people is appalling causing the pile o f solid wastes in the vicinity of the residential areas itself. Even though there is a proper system of collection, segregation & disposal of wastes, it is a serious environmental concern which has to be addressed separately.
Chennai witnesses 425 new vehicles put on road every day causing pressure for motorable and parking space. Increase in impervious increasing the flood severity and later drought to follow. Increase in road space is accounting to only 3 -4% when comparing with the developed cities like London (20-25%) [5]

Master Plan & Flood Mitigation in Chennai -A Quick review
Flood Allev iation Scheme funded by Govern ment with a cost Rs.3000 million was launched in 1998 focusing main ly on structural measures with the objectives like adequacy of flow in the arterial drainage system, safeguard against tidal and fluvial flooding, removing imped iments, relocation and rehabilitation of encroachers. Cleaning of certain waterways and lakes was also undertaken under packages 2 and 3 of the scheme.
Chennai City River Conservation Project wh ich was launched in 2000 [2] is aimed to imp rove the waterways, with an estimated outlay of Rs.17, 000 million. The Master Plan 1992-1993 incorporated Madras Metro Flood Relief/ Storm Water Drainage study outcomes in the form of structural and non-structural measures. Funds under JNNURM project have been visualized for imp lementation of underground sewerage schemes and detailed project reports are being developed. In 2010, the State Govern ment has launched a massive flood mit igation project for the city, involving construction of new micro and macro drainage systems in four basins and making imp rovements to existing drainage, at a cost of Rs.1, 447 crores under JNNURM. The works like improvements works to divert surplus water, desiltation, strengthening existing city drainage network, etc.,

Findings & Recommendations
Both humans and nature put together the ground for the perennial flood tribu lations. The immediate need is to create a scientific inventory of water bodies and delineate flood zones within the city. The flood zone will have to be identified based on the location of the water bodies, natural drains, water shed area and it has to be made as a no building zone. More campaigns have to be conducted at the local level in order to create awareness to the public about the causative factors for the flood disasters. In addition to the above, the wide-ranging management measures will help Chennai to be relieved fro m the recurrent flood menaces almost every monsoon.
An integrated approach, therefore, needs to combine watershed and l and-use management wi th development pl anning, engineering measures, flood preparedness, and emergency management in the affected l owl ands, while taking into account the social and economic needs of communities in both the highland source areas, and also the lowl and flood-pr one areas.

1) An integrated approach in Flood control and Management:
It can be done by creating an unified flood management agency which acts as a nodal group to carry out the function of planning, co-ordination and monitoring of all the existing bodies like CM DA, Corporation of Chennai, Slu m Clearance Board, CMWSSB, etc., in addition to the Disaster management agency 2) Preparation of Topographical Map: Accurate topographical map (at least for the flood prone areas immed iately) should be prepared by the local authority using GIS through digital elevation and terrain mapping.

3) Distinguished Chennai River Restoration programme:
It will support to alleviate the flood issues to a considerable level in addition to the Lake conservation programme [3].

4) Prevention of Pollution:
Impeding the disposal of untreated sewage, sullage and solid wastes will reduce the problem o f choking the waterways which magnifies the flood crisis.

5) Clearing off the encroachments near the water bodies:
All encroach ments in and around the water bodies and flood plains should be cleared off and they have to be rehabilitated in other areas will subsequently reduce the flood crisis 6) Scientific study about flood pattern: There is an immed iate requirement about the study of flood pattern at least for 5 years using hydrological and hydraulic modeling techniques which guides us with a strategic planning collectively. 7) River-front water development plans will help the stakeholders in managing the flood control plan effect ively and also creates awareness to the public also about the advantages in maintain ing the water resources. 8) A rapid assessment of flood inundation mapping is required before the monsoon starts so as to effectively allev iate the flood risks. 9) Flood Mitigation Programmes: Construction of raised platforms, Flood walls, town protection works should carried out and monitored for effective mit igation of flood menace. 10) Water shed management: Timely cleaning, de-silt ing and deepening of natural water reservoirs and drainage channels (both urban and rural) have to be taken up. 11) Increasing Green cover: It requires more of p lanning and regulatory control over the open space and ground cover.

12) Public Awareness:
People should be made aware about the flood preparedness, response and mitigation measures.
The above list of strategies is an illustrative and not an exhaustive but once implemented effect ively will reduce the flood risks efficiently. Finally the approach in imp lementing the above said strategies should be at the micro to macro level approach for a fruitful result.