Integrated urban water resources management strategy for a smart city in India

Economic growth of any nation like India depends on growth of cities. In India 31% of the total population exists in urban areas. The smart city mission of India was established with the objective to deliver the basic requirements of the citizens in a sustainable manner. Madurai city located at Peninsular India with a 1.4 million population was taken for this study. The objectivewas to develop an integrated urban water management strategy after analysing all the components of the urban water cycle such as rainfall, runoff, groundwater and wastewater. The population forecast for 2021 was carried out for the Local Planning Area of 726.34 km and the water demand was calculated as 109 Mm/year. To meet the demand, runoff from the average rainfall was estimated as 393 Mm/yr using the SCS-CN method. The storage capacity in the water bodies to store the surface water was estimated as 156 Mm/yr and groundwater recharge potential was estimated as 22 Mm/yr. The integrated urban water management strategy developed, shows that there is a huge potential for rainwater storage at the surface level and subsequent recharge through artificial recharge techniques.


INTRODUCTION
The rapid growth of population, urbanization, changes in living standards, increase in irrigated agriculture, and altering consumption patterns has increased water demand.
Water management is gradually becoming a crisis faced by governments all over the world. The world population is expected to reach 9.1 billion in the year 2050 with 69% of people living in cities (93% of such increase is expected to happen in developing countries) resulting in a 55% increase in water demand (Connor ). Extractions of water have tripled in the past 50 years causing a decline in freshwater resources. By the year 2030 water supply is expected to be reduced by 40% as a result of urbanization and industrial development, thus impacting both the quality and quantity of available water resources (Van Leeuwen ). In the 21st century, the water crisis will be more related to management than scarcity and stress (Tundisi ). Climate change, more recurrent and extreme weather events are known to change the quality, quantity, and seasonality of water available to the urban region and their economic condition (Singh et al. ).
Faced with all these challenges, there is a critical need to improve the existing sources of water with more sustainable alternatives. For improvements and augmentation many approaches, both modern and traditional, persist throughout the world for efficiently managing the available water. The conventional method of urban water management follows an isolated approach for each component of the urban water cycle (freshwater, storm water and wastewater) hence developing a new strategy for proper urban water management is required (Cosgrove & Loucks ).
The world is rapidly changing to integrated urban water management as it follows a synchronized approach considering all components of the urban water cycle. It is a paradigm shift to attempt to halt the growing water stress faced in several cities worldwide (Gambrill et al. ). It instils the practice of managing freshwater, wastewater, and storm water considering both urban development and basin management (Bahri ). So far, nearly 80% of countries have laid the foundation for integrated water resource management (UNEP ).
The smart city mission concept was initiated in India to meet the requirements of people residing in urban cities.
The main focus of the smart city concept is the development of a model that can be reproduced in similar environments. Madurai is one among 100 smart cities selected by the government under the smart city mission.
The area considered for the study was Madurai Local Planning Area (LPA) of 726.34 km 2 . The purpose of forming an LPA is to take a detailed look at a specific area, identifying and analysing the various issues of relevance, before establishing and preparing a master plan for the future development of the area. The main aim of the study is to propose a suitable integrated water resources management strategy for Madurai LPA to manage the predicted water demand by the year 2021. The strategy was developed by estimating the status of different components of the urban water cycle such as rainfall, runoff, groundwater, surface water (river and water bodies), and treated wastewater in the study area.

STUDY AREA
Madurai, one of the ancient cities of India, is located at 9 93″N and 78 12″E. This city was identified as a smart city by the government of India in the year 2015. The corporation limit of the city was extended from 52.18 km 2 to 147.9 km 2 in 2011. The water demand of the city with a total population of 1.4 million (as per the 2011 census) was found to be 209 million litres per day (MLD). With the existing water resources, the city corporation supplies only 115 MLD for domestic use, resulting in a water shortage of 94 MLD. The temperature in Madurai was found to range from 21 C to 38 C with an annual average rainfall of 850 mm (Alagarsamy ).
The Madurai LPA covering 726.34 km 2 was formed in the year of 1974 based on the Tamil Nadu Town and Country Planning Act 1971. It comprises the Madurai corporation area (both old (52.18 km 2 ) the existing area (147.9 km 2 )) and the environs (Figure 1). The total population in the study area was found to be 1.9 million (as per the 2011 census).
With the increase in population, Urban sprawl is expected to expand towards the Madurai LPA. Hence there is a need to ensure the status of water resources in the region and to propose a plan for its proper management.

MATERIALS AND METHODS
The methods adopted for this study are as shown in Figure 2.
Initially, population data for Madurai LPA was collected for 7 decades (1951, 1961, 1971, 1981, 1991, 2001, and 2011) and the population for the year 2021 was predicted using the arithmetic mean method, geometric mean method, and incremental increase method. Water demand and wastewater generation rates were calculated for the year 2021 considering the projected population. Rainfall analysis was performed by adopting the Weibull method to find the 75% dependable rainfall using 10 years' rainfall data collected from the Public Works Department (PWD), Madurai and overall average precipitation of the region was also estimated using the Thiessen polygon method using Arc Geographical Information System (GIS) software version 9.2. Then with the daily rainfall data and antecedent The groundwater recharge potential was estimated using the fluctuation method by considering 12 years of water level data collected from the PWD, Madurai. The status of water bodies in the study region is also discussed based on the data collected from PWD. In addition to the above discussion, suitable methods and options for implementing artificial recharge techniques are also suggested. Finally based on the results an integrated water management strategy was developed.

Population forecasting
The population estimation is essential to recognize the current and future water demands. The population data of the past 7 decades (1951, 1961, 1971, 1981, 1991, 2001, and 2011) were collected from the statistics department of

Madurai, Sivagangai & Virudhunagar districts, and Census
Reports. The population in the year 2021 was predicted using the arithmetic mean method, geometric mean method, and incremental increase method (Alagarsamy ). Of the above three methods, the value predicted using the incremental increase method (Table 1) was adopted for further water demand calculation.

Water demand & wastewater generation estimation
Water demand of the study area in the year 2021 was estimated using Equation (1)   It is estimated that 80% of the total water supplied will be generated as wastewater as per CPHEEO norms (Reddy & Kurian ). Therefore, wastewater generation in  (Table 2) was calculated using Equations (2) and (3) where: n is the total number of events in the data series m is the order number of each event when the data are arranged in descending order.
Precipitation is not uniform over the area, correspondingly temperature, humidity, and several other influencing factors also vary from place to place. Hence effective uniform depth of precipitation over the study area was also calculated using the Thiessen polygon method (Mishra et al. ) as shown in Figure 3. This is a graphical technique used to calculate rainfall based on relative area. The mean areal depth of rainfall over the study area was found to be 782 mm using Equation (4): where: P avg is average rainfall in mm P N is rainfall for an individual station in mm A N is area of influence for an individual station in km 2 A is total area in km 2 .  The overall analysis of the rainfall trend showed a nonlinear variation and peak rainfall was observed during September, October, November, and December, i.e., and Wet (Amutha & Porchelvan ) as shown in Table 3.
The quantum runoff generation was calculated using Equation (5) and the result is represented in Figure 5: where: Q is accumulated run off or rainfall excess in mm P is rainfall in mm I a is initial abstraction in mm (surface storage, interception and infiltration prior to run off) and it is given by Equation (6): where S is potential maximum retention and it is given using Equation (7): where CN is curve number estimated using Equation (8): where: CN w is weighted CN  A is the total area in km 2 .
The estimated runoff values were correlated with the rainfall data. From this correlation, it is clearly understood that the antecedent moisture condition of the soil plays a dominant role in the quantity of runoff generated. From the runoff estimation, it is also clear that possibilities for dry conditions prevailed during the last two years (2012 and 2013), but during that case too, the runoff generated was enough to compensate the water demand in the study area.

Groundwater recharge potential estimation
The groundwater recharge potential was assessed to find whether there is enough storage capacity in the subsurface to store the runoff generated if we adopt suitable recharge options to improve the water source. Under the study area, 10 bore well stations and 5 open well stations were located and their monthly groundwater level data collected from the  The groundwater potential estimation (GWP) was carried out using the fluctuation method (Equation (9)) ( Jeykumar & Chandran ) assuming specific yield for the region as 2% (CGWB a).

Fluctuation method
Average groundwater potential where: A is area in km 2 ΔS is specific yield in % ¼ 0.02 Δh is average change in water level in m.
The groundwater potential estimated using the fluctuation method was 22 Mm 3 as given in Table 5. There is a reasonable amount of groundwater potential to store the runoff generated from the rainfall. Hence It is necessary to  The following two options can also be considered while adopting any of the above-mentioned recharge techniques: Option 1: There are two STP's within the study area and they have the capacity to treat 171 MLD of wastewater.
Hence wastewater generated in the region can be treated in the STPs to meet the standards (Sengupta ) and using 13 channels systems that exist within extended corporation limits (Hardy ) these treated wastewater can be stored in the water bodies (system tanks) through a cascade system. Nearly 8% of the study area is covered with water bodies. This stored treated wastewater can be further used for the non-potable purpose and indirectly the wastewater will also recharge the subsurface.
Option 2: Based on LULC classification it was identified that nearly 3% of the study area exists as wasteland. These lands can be used for executing recharge structures. Also, these lands can be planted with native vegetation to control runoff in the region, avoid evaporation of runoff water, and to enhance natural recharge in the region.

Surface water status
Madurai is a city with an average annual rainfall of about 850 mm. People depend upon surface and subsurface water resources to meet their water demand. To manage the water demand water bodies(tanks) status, and their potential as water recharge structures were also discussed in this study.
The details of surface water bodies located within the old corporation limit and LPA was collected from toposheet and the PWD. The total number of tanks within the old corporation limit was identified as 25. Out of it, only five tanks were found to be in good condition with a storage capacity

Integrated urban water management strategy
Based on the results, an integrated urban water management strategy was developed as shown in Figure 8. It represents all possible ways by which the precipitation can be

CONCLUSIONS
The smart city mission of India focuses on sustainable, inclusive development and to create a replicable model which will act like as a light house to other aspiring cities. Keeping this as a point of focus this study was undertaken for Madurai, a smart city with 1.4 million population. By assessing the existing water resources potential of the city an integrated urban water management strategy was developed. The results of the study reveal the following: • Population of the study area is forecasted for 2021 using an incremental increase method as 2.2 million. The present water supply system can satisfy only 38% of predicted water demand hence, all other feasibilities are explored in this study.
• The mean area depth of rainfall was estimated as 782 mm and the runoff generation was 393 Mm 3 /yr which is 3.6 times higher than the predicted water demand (109 Mm 3 /yr).
• Groundwater recharge potential was estimated as 22 Mm 3 . By adopting suitable recharge techniques in the LPA area of 726.34 km 2 especially in the water bodies around 40% of runoff generated can be stored efficiently.
But the interconnecting systems between the river, channels and system tanks have to be restored to their original condition that existed 5 decades before.
• The predicted urban population will be generating 87 Mm 3 /yr wastewater, out of which 71% of wastewater can be treated with existing advanced treatment facilities functioning with the technology of the Cyclic Activated Sludge Process. As this treated wastewater met the standards prescribed by the government (BOD 30 mg/l), this can be stored in water bodies and used for urban agriculture which has been practiced in this region for more than 35 years.
• Integrating the various sources such as treated water from the Vaigai reservoir, surface runoff generated from the rainfall, groundwater recharge using artificial recharge structures and reuse of treated wastewater will meet the future demand.