1. Introduction

• Background and demographics 

Ahmedabad, the largest city of Gujarat state, has a population of 5.6 million in the municipal area and 6.3 million in the urban agglomeration area, as per 2011 census. The municipal area is under the jurisdiction of the Ahmedabad Municipal Corporation (AMC), whose limits were last extended in 2020 to cover an area of 505 sq.km. As its peripheral areas develop, the city limits have been extended over the years. Whereas the Ahmedabad Urban Agglomeration, which is governed by Ahmedabad Urban Development Authority (AUDA), includes five growth and 169 villages besides the municipal area, and covers a total area of 1,866 sq.km.

• City and Water

Sabarmati river flows through the city which used to be a major water source. The city has seen elaborately designed step wells in its past. Over the years, the water sources have changed. Ahmedabad has used groundwater through wells and borewells, as well as borrowed water from Dholka – branch of Sabarmati, Dudeshwar water works, Dharoi reservoir, Shedhi branch of Mahi canal and Narmada canal through Sardar Sarovar Project. Ahmedabad Urban Development Authority (AUDA) has notified 79 lakes as urban lakes within its jurisdiction.

• Land Use

A project by AMC and AUDA has been taken up to interlink 45 surface bodies (ponds & lakes) and recharge it with storm water and surplus surface water of Narmada Canal, under the ‘National Lake Conservation Plan’. Ahmedabad has nearly 201 municipal parks and gardens, 4 major industrial cluster areas. Out of the total AUDA land, 570 sq. km. (30.5%) is agricultural land, There are 9 STPs in the city in Pirana, Vasana and Vinzol areas.

2. Historical Context

Sabarmati is an important river flowing through the city of Ahmedabad, and has been an important source of water for its residents. Sabarmati river originates in the Aravalli ranges of Udaipur, Rajasthan and flows through Ahmedabad and flows into the Arabian Sea through the Gulf of Khambhat. The history of the city, founded in 1411, is closely tied and organised around the Sabarmati River. The river was a crucial source for domestic water use, farming and other recreational purposes. Over the years, a few dams have been built on the river, like the Dharoi dam built in 1976 to prevent flooding.

Ahmedabad also has several well designed, elaborately carved stepwells or vaavs, which were functional in olden times. They were critical source points for traders travelling for work, local residents and their domesticated animals.

In recent years, Narmada canal, which is part of the Sardar Sarovar project supplies water to the city along with other sources. The canal meets the North of the city, in the upstream area of Sabarmati and water from the canal is diverted to Sabarmati at this point. This water is retained in the Sabarmati river through Vasna barrage (built in 1976 for controlled irrigation purpose) in the downstream of Sabarmati river. Fatehwadi canal diverts water from Vasna barrage to villages in the South and South-West of Ahmedabad for irrigation purposes. 

3. Ecological Context

3.1 Ahmedabad Topography

Ahmedabad city is mostly flat in terms of topography, except for mild undulations because of stabilized dunal landforms. The city is located in a sandy and dry area. The elevation across the city ranges from 40 to 60 meters above mean sea level, with major slope towards the South. River Sabarmati flows through the city and bifurcates the city into eastern and western parts.

3.2 Ahmedabad Rainfall 

Ahmedabad is characterized by hot and dry summers except during the southwest monsoon seasons, which receives the most rain between June to September months. October and November constitute the post-monsoon or retreating monsoon season. Long-term average annual rainfall recorded by IMD station at Ahmedabad is 799.6 mm across 33 rainy days. Most of the rainfall (about 766 mm) is received from the south-west monsoon between June to September.

3.3 Ahmedabad Geology 

It is important to look at the geological formation of Ahmedabad beyond the city’s scale to get a broader understanding. The main river basin in Ahmedabad district is the Sabarmati river basin. The river originates from Aravalli ranges in Rajasthan and discharges in the Arabian sea at the Gulf of Khambhat. The area is formed of Quaternary alluvium deposits, which is a fairly young formation consisting of a combination of loose gravel, kankar, sand, silt or clay. Some  South-Western parts of the district consist of Basalt rock. Groundwater in this alluvial formation is available in the form of confined and unconfined aquifers. Ahmedabad district heavily relies on deep bore-wells for water supply schemes. This has led to an increase in the number of bore-wells and caused over extraction of groundwater over years. The result has been a  sharp decline in groundwater levels and deterioration of quality of water. 

The Central Ground Water Board assesses the status of groundwater development in each taluka across the country and categorises them in terms of availability and quality of groundwater. Out of  the 10  talukas in Ahmedabad district, 1 has been categorized as over exploited , 1 lies in Critical category, 2 are categorized as Semi critical, 1 is categorised as saline block, while 5 fall under Safe category. Overall the district is categorized as Semi critical. 

On studying the geological characteristics of urban Ahmedabad – Gandhinagar areas, it was found there are alternating sandy and clayey layers with 'kankar' and gravel beds occurring at depths. Within the depth of 250 m of this multilayered aquifer system, two major aquifer units could be identified. The shallow depths of the first 40-50 m of the unconfined aquifer is uniform in character and composed of medium to fine sands, silt with kankar and minor clay layers. At lower depths several confined aquifers are formed by the alternating sandy and clayey horizons. One of such section of urban Ahmedabad area showing unconfined and confined aquifer system is reproduced below: 

3.4 Ahmedabad Rivers

Sabarmati river is the principal river of the district. It originates from Dhebar lake in Tepur village of Udaipur District, Rajasthan and finally discharges into the Gulf of Khambhat near Vataman village of Dholka taluka. It used to be a major source of water for the city’s residents. As the city's population and hence its water demand grew, dependency on groundwater increased as well as water was previously being imported from Dharoi dam and now from Narmada canal among other sources. Within the city and along the edge of Sabarmati river, the riverfront was developed for use since 2012. This is a 15 km stretch, which intends to serve as a public space for the city. Vatrak, Khari, Meshwo, Bhogavo, Bhadar, Rodh, Shelwa and Andhli are other rivers flowing through the district of Ahmedabad beyond the city limits. 

Khari river The Khari river runs almost parallel to the Sabarmati towards east. The ‘Kharicut canal scheme’ is one of the oldest irrigation schemes of Gujarat that passes through eastern part of Ahmedabad City and also serves as ‘Storm Water Drainage’ during monsoon. 

3.5 Ahmedabad Lakes

There are 1411 lakes within the AUDA boundary and 59 lakes within the AMC boundary. Some famous urban lakes are Chandola, Kankaria, Vastrapur lakes. Like most cities experiencing urbanisation and its effects, Ahmedabad also witnesses its impacts on lakes such as encroachment over lake periphery, discharge of grey water and solid waste dumping in lakes, filling up lakes for real estate development, disconnecting lakes from its natural drainage networks.

If RWH is properly planned within all the small, medium and large lakes of Ahmedabad, the runoff from these lakes could suffice for 56% of Ahmedabad’s annual water needs. This would mean intervening from the technical and technological aspects such as creating storm water drains, treatment of lake edges, assessing storage and percolation capacity of lakes, rainwater storage, designing outlet for excess water. From governance and management perspective, it would mean active involvement of local governing bodies like AMC and AUDA to maintain, monitor the lakes, its functioning and water quality. Involvement from the citizens may also be required through awareness and sensitisation programs.

4. Institutional Context

• The main authority responsible for the water supply, sewerage and storm water  drainage within the city of Ahmedabad is Ahmedabad municipal corporation (AMC). 

• Although, Ahmedabad Urban Development Authority (AUDA) is not directly responsible for provision of water, the  execution of works is among the attributions of the AUDA. Lake development was initiated for some lakes in Ahmedabad for strategic storm water networking by AMC and AUDA. 

• Gujarat Water Supply and Sewerage Board (GWSSB) is responsible for rapid development and proper regulation of water supply and sewerage services in the State of Gujarat. 

• Water and Sanitation Management Organisation (WASMO) works in rural areas of Gujarat state to strengthen its drinking water supply and sanitation infrastructure through technical as well as social interventions. 

• Gujarat Water Infrastructure Limited (GWIL) is involved in establishing a bulk water pipe grid based on Narmada water in Gujarat state for its water needs. 

5. Supply & Demand Context

Ahmedabad's daily water demand is calculated on the basis of 180 litres per capita per day (lpcd). Ahmedabad city has a good coverage (90%) of taps at household level for potable water which is targeted to reach 100% achieved through AMC, its urban local body. The general scheme of water supply in the city is:

(a) Source →  (b) treatment plant → (c) trunk mains → (d) local water distribution stations (WDS from here on) and underground tanks → (e) residences.  

The city receives 1485 MLD water through its various sources such as interbasin transfer through canals and groundwater withdrawn through borewell. As seen in the diagram below, major water supply in the city is through Narmada main canal, Dholka branch canal, Shedhi branch canal. This raw water is treated at Kotarpur, Jaspur and Raspur water treatment plants respectively, and supplied to the city. Borewells across the city account for 130 MLD water requirement.

Most households receive water through the AMC supply network for two hours in a day, and sometimes additionally for an hour in Summer evenings. In case, a housing society experiences inadequacy of supply, they dig borewells and withdraw groundwater for consumption. There are no metered connections in the city. 

6. Economic Context

Cost of water

The cost of getting a connection for water supply from municipal corporation in residential property ranges from Rs. 100 to Rs. 20,000 depending on pipe diameter and metered connection. The table below gives details of water supply connection. The billing of water is not based on consumption of water but on taxes fixed in relation with property tax. In consequence, the water and conservancy taxes are levied on the basis of area property.

Water Tax

• Residential properties are charged between 30% of the general tax. And the general tax varies based on type of property and its area, details of which it can be found in table below. 

• Non residential properties are charged between 30-40% of the general tax, according to the area.

Conservancy Tax 

All properties are charged 30 - 40% of the general tax based on type of property and its area.

Rainwater management as per GDCR (Comprehensive Development Control Regulations – 2017, UD & UHD, Govt. of Gujarat) -  

Rain water harvesting is mandatory for all buildings with ground coverage 80 sq.mt and above. The system of storm water drainage and storage in reservoirs and recharge should conform to one of the following specifications: 

• For Buildings with ground coverage above 80 sq.mt and below 500 sq.mt: 

Percolation Pit or Bore Recharge shall be provided in the marginal space around the building. Such pits shall be filled with small pebbles, brick jelly or river sand and covered with perforated concrete slabs as illustrated below: 

• For Buildings with building‐unit area above 500 sq.mt and up to 1500 sq.mt: 

Percolating Well with Rain Water Harvesting System shall be provided as illustrated below (up to ground first river):

• For Buildings with building‐unit area above 1500 sq.mt and up to 4000 sq.mt: 

Percolating Well with Rain Water Harvesting System shall be provided for every 4000 sq.mt as illustrated above (up to ground second river). 

• For Buildings with building‐unit area above 4000 sq.mt:                                              

One Percolating Well shall be provided as per Regulation no. 3 for every 4000sq.mt land area. As an alternative to providing multiple percolating wells, a Water Retention Pond with minimum capacity of 300,000 litres with a percolating well for every five percolating wells or part thereof shall be permitted as an alternative.  

Rainwater design factors as per NBC 

Estimate of the quantity that reaches the storm water drain (runoff) depends on the following factors: 

1. Type of soil and its absorption capacity determined by its soil group. 

2. Ground slope and the time in which the area is drained. 

3. Intensity of the rainfall for a design period.

4. Duration of the rain/storm.

In the calculation of rainwater harvesting volume, the important factor to be considered the coefficient of water runoff for different surfaces which are as follows:

Type of Surface                                                     Coefficient of Runoff

Concrete roof area                                                                0.9

Paved podium areas and asphalted roads                         0.8

Unpaved ground                                                                   0.3

Lawns and parks                                                                  0.15

The factors that decide the quantity of rainwater entering are:

a) Intensity of rainfall, and 

b) Time of concentration selected for rainwater pipe. 

A bell mouth inlet at the roof surface is found to give better drainage effect, provided proper slopes are given to the roof surface. The spacing of rainwater pipes depends on the locations available for the down takes and the area which each pipe serves. The spacing will also be determined by the amount of slopes that can be given to the roof. The recommended slopes for the flat roofs with smooth finish would be 1:150 to 1:133, with rough stone/tiles 1:100 and for gravel set in cement or loosely packed concrete finish 1:75 to 1:66. The effective strainer area should preferably be 1.5 to 2 times the area of pipe to which it connects to considerably enhance the capacity of rainwater pipes.