Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Karunakaran, K.

Mudgal, B. V.

Suriya, S.

English

Hydraulic Engineering Repository

Conference Paper, Published VersionSuriya, S.; Mudgal, B. V.; Karunakaran, K.Effect of Urbanization on Flooding: Adyar River a CaseStudyZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Kuratorium für Forschung im Küsteningenieurwesen (KFKI)Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/109974Vorgeschlagene Zitierweise/Suggested citation:Suriya, S.; Mudgal, B. V.; Karunakaran, K. (2010): Effect of Urbanization on Flooding: AdyarRiver a Case Study. In: Sundar, V.; Srinivasan, K.; Murali, K.; Sudheer, K.P. (Hg.): ICHE2010. Proceedings of the 9th International Conference on Hydro-Science & Engineering,August 2-5, 2010, Chennai, India. Chennai: Indian Institute of Technology Madras.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.EFFECT OF URBANIZATION ON FLOODING: ADYAR RIVER A CASE STUDYS.Suriya 1, B.V.Mudgal 2, K.Karunakaran 3AbstractOne of the effects of urbanization is an increase in the magnitude and frequency of  floods, and its associated risks to the communities. The growth of urban settlements has put  tremendous  pressure  on  water  supply,  drainage,solid  and  liquid  waste  disposal.  Urbanization  of  the  catchments  brings  dramatic  changes  in  hydrology,  i.e.,  decrease  in  infiltration or increase in runoff, increased peak flow, reduced time of concentration. Two rivers  namely  Cooum  and  Adyar  flow  through   Chennai  city.  These  rivers  are  non  –  perennial. Due to encroachment along the banks of these rivers and non – implementation of  the  existing  regulations  due  to  fragmented  and non  –  integrated  agencies;  the  effect  of  flooding tends to be severe. Development along stream channels can alter the capacity of the channel to convey water and can increase inundation levels. The Adyar river flows through the Chennai Metropolitan Area (CMA), which has  very high density of population (Population of CMA: 70.41 lakhs as per 2001 census data). A  number of irrigation tanks in the upstream discharge their surplus water into the river. In the  years 1976, 1985, 2005 and 2008, the river overflowed on its banks, causing extensive flood damages. Hence, it is essential to analyze the flow pattern of the river to minimize the flood  hazard. This study focuses on the present condition of the river and compares it with the  conditions  of  river with 1999 data.  Databases were prepared making use of  Geographic  Information System(GIS) on land use classification for 1976 and 2005.Water surface profiles  along the river reach, for floods for various return periods were computed using HEC – RAS model. Key words: urbanization; flooding; land use; water surface profile; HEC – RAS ,GIS1 Research Scholar, Centre for water resources, Anna University, Chennai-600025, PH +91 9894227599, email: suriya_svu@yahoo.co.in2 Assistant  Professor,  Centre  for  water  resources,  Anna  University,  Chennai-600025,  email: bvmudgal@annauniv.edu3 Director, Centre for water resources, Anna University, Chennai-600025, email: kkaruna@annauniv.edu Proceedings of ninth International Conference on Hydro-Science and Engineering (ICHE 2010), IIT Madras, Chennai, India. 2 - 5  August 2010 674INTRODUCTIONUrbanization  is  one  of  the  anthropogenic  activities  that  result  in  the  loss  of agricultural  land,  environmental  degradation  and decline  in  natural  vegetative  cover.  The conversion of rural areas to urban areas has increased tremendously which affects the natural functioning of ecosystems.  In urban areas, most of the land surface is covered by impervious material which reduces infiltration and accelerates the runoff process leading to the problem of flooding.  The land use change has a considerable impact  on the runoff nature and its related hydrological characteristics. Significant changes in land use would affect the overall health  and  functioning  of  a  watershed.  Rapid  urbanization  within  river  catchments  has accentuated the flooding problem. Although flood hazard is natural, human modification and alteration of nature’s right of way can aggravate the problem, the disastrous consequences are dependent on the degree of human activities and occupancy in vulnerable areas. Urbanization  is  taking place rapidly in South Chennai, a coastal  city  which is located in North Eastern corner of Tamilnadu State, India. This leads to increase in human settlements, industrial growth and infrastructure development in flood hazard areas thereby decreasing  the  use  of  land  resources  for  agriculture  and  economic  development.  This substantial  change  in  land  cover  due  to  urbanization  has  magnified  the  intensity  and magnitude of flooding by restricting the natural flow of flood waters. Due to the growth of infrastructure  in  IT,  industries  and housing sectors,  there is  drainage congestion  of flood water during monsoon. Hence for the same amount of rainfall, greater is the flooding. The flood events of the years 2002, 2005 and 2008 have been magnified due to improper drainage facilities. Moreover, due to intense urbanization, inundation occurs even for a low intensity – short duration storm. The present work aims to assess the relationship between urbanization and flooding.  HEC –RAS simulations were performed to generate water surface profiles.OBJECTIVESThe objectives of the study are to Develop land use map by applying GIS as a tool Determine  the flood levels  along the river bank using HEC RAS for different return periods Establish a relationship between urbanization and floodingSTUDY AREAThe micro watershed that contributes flow to the Adyar River is taken and then delineated as study area. The latitudes and longitudes of the study area are  13° 01' 09"N, 80°00' 44"E and 13° 00' 46"N, 80°16' 37"E. The total area is about 146.24 sq km. Figure 1 shows the delineated study area of the Adyar River from the micro watershed.675        Fig. 1. Study area mapMETHODOLOGYThe steps followed in the study are Land use classification Calculation of time of concentration using Arc GeoHMS Calculation of water surface profiles for steady flow using HEC RASLand use map (1976) was prepared using toposheet as base map in Arc Map 9.3. LISS III imagery taken in December 8, 2005 was processed and classified using Maximum Likelihood method in ERDAS Imagine 9.0 and digitized in Arc map platform to produce land use map (2005). Figure 2 and 3 show different land uses in the study area for the year 1976 and 2005 respectively. Table 1 shows the change in land use for the year 1976 and 2005.676Fig. 2. Land use map (1976) Fig. 3. Land use map (2005)Table 1. Change in land useSl NoLanduseArea in sq km% Change1976 20051 Built-up area 48.601 63.387 302 Canal 0.1480.073 -513 Forest 0.584 0.774 334 Land 51.023 43.099 -165 Plantation 4.173 1.789 -576 River 3.708 3.307 -117 Scrub land 14.703 10.886 -268 Waterbody 23.28 22.924 -2Total 146.22 146.239677Land use change is a major force altering the hydrological processes over a range of temporal  and  spatial  scales.  This  can  affect  the  runoff  generation  and  concentration  by altering  hydrological  factors  such  as  interception,  infiltration  and  evaporation,  and  thus causes changes in the frequency and intensity of flooding. At a catchment scale, such impacts on hydrological processes in turn will significantly influence ecosystem, environment and economy. Therefore a better understanding and assessment of land use change impacts on watershed  hydrologic  processes  is  of  great  importance  for  predicting  flood  potential  and mitigation  of  hazard,  and  has  become  a  crucial  issue  for  planning,  management  and sustainable development of the watershed (Ying Chen, 2009).From the table 1, it was found that built area has increased from 33% to 44% and there is a reduction in other land use pattern. The main hydrologic parameters used to represent urbanization conditions are: (a) impermeable area of the basin, understood here as the proportion of the surface area, for which precipitation enters the storm-water network directly; (b) time of concentration or velocity of the flow through the basin (Nestor, 2001). Therefore, time of concentration was calculated using TR 55 (Technical Release 55) method by giving the stream network, Digital Elevation Model (DEM), Curve number from land use maps and precipitation as inputs in Arc GeoHMS. It was found that travel time has decreased from  3.34 hours (1976) to  2.2 hours (2005).  It  reveals  that  land use change is  a  major process altering the hydrological processes in the study area. It can also cause changes in the frequency and intensity of flooding.Hydrologic Engineering Center’s River Analysis System (HEC-RAS) is used to  perform one  dimensional  hydraulic  calculation  for  the  entire  stretch  of  Adyar  River. Geometric data and steady flow data are the main inputs to run HEC RAS model. The basic geometric data consists of the river system schematic, cross section details, reach length etc. The cross sectional details of the river are obtained from Public Works Department (PWD), Chennai.  The  steady  flow  data  consist  of  flow  regime,  boundary  conditions  and  peak discharge.  For this study, the flow through the river is assumed as mixed flow. In a mixed flow regime, boundary conditions are necessary at the upstream and downstream ends of the river.  For this analysis, normal depth is taken as boundary condition in upstream and known water surface elevation (tide levels) in downstream. The rational method is used to determine the peak discharge using the formula,Q=0 .00278CIA                                                      Q = Peak discharge (m3/sec)            C = Runoff coefficient               I = Intensity of rainfall (mm/hr)              A = Drainage area (km2)     The rainfall intensity is obtained from the I-D-F (Intensity – Duration – Frequency) curve diagram and it was selected corresponding to the time of concentration as duration in minutes for the return period of 1.1, 1.5, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100 and 200 years. Time of concentration for the year 1976 was taken as 202 minutes and for the year 2005 was taken as 132 minutes. The peak discharge is calculated for all the return periods and entered (1)678accordingly. The calculated peak discharge for the study area with different return periods for the land use pattern of year 1976 and 2005 are given in figure 4.Fig. 4. Peak discharge for the land use in the years 1976 and 2005.   The top width of the river varies from 386.4 m near the sea mouth to 117.97 m at a distance of 7.2 km from the sea mouth. The depth of the river varies from 2.53 m to 10.72 m. The model is run for the years 1976 and 2005 for all the return periods mentioned above. Model results are in the form of water surface profiles, cross sectional plots, cross section profile  tables  and X-Y-Z perspective  plots.  It  is  seen  from the  results  that  the  model  is capable of simulating the flow profiles for different return periods.  Figure 5 and figure 6 shows the water surface profiles for the Adyar river from Chembarambakkam tank to sea mouth for the year 1976 and 2005 respectively.679Fig. 5. Water surface profile plot (1976) for the return period of 100 yearsFig. 6. Water surface profile plot (2005) for the return period of 100 yearsCONCLUSIONSWith the change in land use pattern, there has been a rise in impervious area (Figure 3 and Table 1). From the present study it is seen that the peak discharge for a given return period is lower for 1976 land usee pattern. Whereas, for the 2005 land use pattern, flooding occurs  even  for  lower  return  period  and  lower  intensity  of  rainfall.  Due  to  increased impervious  area,  precipitation  responds quickly reducing  the time to peak and producing higher  peak  flows  in  the  river.   This  proves  that  there  is  a  strong  relationship  between 680urbanization and flooding. Proper assessment of increasing flood risk to the study area from rapid  urbanization  cannot  be done without  the integration  and analysis  of  land  use data. Therefore, planned land use should be explored, proposed and implemented to minimize the effect of flooding. Both engineers and policy makers should come up with innovative ideas for effective flood management strategies, in an integrated framework. ACKNOWLEDGEMENTSThe  authors  gratefully  acknowledge  the  support  received  from  the  Crossing Boundaries Project.BIBLIOGRAPHYNestor  A.  Campana  and  Carlos  E.  M.  Tucci  (2001),  ‘Predicting  floods  from  urban development scenarios: Case study of the Diluvio basin, Porto Alegre, Brazil’, Urban water 3: pp 113 – 124  USACE, 2002, HEC-RAS River Analysis System, User’s Manual, U.S. Army Corps of EngineersYing Chen, Youpeng Xu, Yixing Yin, 2009 ‘Impacts of land use change scenarios on storm runoff generation in Xitiaoxi basin, China’, Quaternary International, pp 1 – 8   681

Effect of Urbanization on Flooding: Adyar River a Case Study

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Effect of Urbanization on Flooding: Adyar River a Case Study

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