Hold the rain

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Urbanization poses a threat to our natural environment: it leads to water scarcity, disasters, loss of biodiversity and more. Urbanization, when carried out optimally and sustainably, can offer a solution to emerging urban problems.

The Odisha Government’s Housing and Urban Development Department (HUD) presented an excellent model. It is about “catching the rain”.

The rapid growth of urban areas has affected the natural recharge of groundwater. As a result, surface water runoff has increased, thus limiting its infiltration into the soil and causing water scarcity.

Rainwater harvesting can offer an excellent solution in such situations. Observing the erratic rainfall and increasing frequency of flooding, many states have already adopted such measures to install a rainwater harvesting system in their cities to reduce surface water runoff.

Odisha leads by example. The Delhi-based think tank Center for Science and Environment is its knowledge partner. The state has developed 12,000 Rainwater Harvesting Structures (RWHS) to facilitate water conservation and groundwater recharge in 2,035 neighborhoods in 114 local urban organizations.

This happened in less than three months, before the onset of the southwest monsoon.

Rainwater harvesting involves collecting runoff from a structure or other impermeable surface to store it for use. The process is used to conserve rainwater that runs off rooftops, parks, roads and open land by collecting, storing, transporting and purifying it.

The state had selected sites to have these structures to meet the statewide campaign Catch the Rain: Where it Falls and When it Falls. This was carried out as part of Mukhyamantri Karma Tatpara Abhiyan (MUKTA), an urban wage employment program for migrant workers.

Over the past decade, most Indian states have seen irregularities in rainfall patterns resulting in a water crisis and drought-like situation in some places, while heavy rainfall has resulted in flooding in d ‘others.

Odisha is no exception: It is a state of surplus water due to its annual rainfall which varies from 1200 mm to 1800 mm, but its spatial distribution is uneven and erratic.

The state receives 76% of precipitation between mid-June and mid-September and the rest throughout the year. Given the uneven rainfall pattern, the only way to use the excess rainfall received is to store it.

The state government wanted to develop a mechanism that would be cost effective, require simple technology to operate, and require the least amount of maintenance. The type of rainwater harvesting system they developed was a pit and burrow which cost Rs 35,000 per unit, required no complex technology, and required less maintenance. It was completed in 7-10 days.

Odisha’s government aims to conserve both runoff from the roofs of schools, hospitals, community halls and other public and private institutions, as well as stormwater runoff from parks, playgrounds, open spaces, vacant lots and roads.

The spacing and number of recharge wells will be based on the porosity and permeability of the soil below 1.8 meters, the average annual precipitation, and the intensity and duration of precipitation in that particular region. For average conditions, a recharge pit 1.2 meters in diameter and 1.8 m deep with a main channel of 15 m is sufficient for 250 m² of the watershed.

The recharging mechanism is also simple. The partial recharge of rainwater from the watershed is done through the loading channel. The excess rainwater received from the loading channel and the rainwater from the area surrounding the pit are recharged with a filled medium.

The sand layer acts as a conventional filter media for surface water. To support it, broken granite shards are provided under the layer of sand. The sand layer filters and retains suspended solids, thus providing a base for the gray / black blanket formed on the sand due to the filtering of clay, silt and colloidal particles.

The filter media in the main channel and the recharge pits act as a porous membrane which allows partially filtered rainwater to reach the soil media interface. The bottom layer of soil acts as a natural filter, making it easier to microfiltrate rainwater before it reaches the water table.

Over time, the top layer turns gray or black, reducing the efficiency of recharging. Thus, the sand in the top layer can be replaced periodically with new layers of sand. The removed layer is rich in organic nutrients which can be used to fill planting sites in the park and open spaces.

The government of Odisha recommended the compulsory construction of 5 RWHS / ward in a notified regional council; 10 RWHS / district in a municipality and 20 RWHS / district in a municipal corporation of 114 urban local authorities. Daspalla, one of Odisha’s NACs, built 80 RWH structures with 138 pits in 16 ULB neighborhoods.

According to Sasmita Pradhan, coordinator of the MUKTA program (a program to reduce unemployment in the state), in Daspalla, 40 self-help groups and 2,898 people were employed for this initiative because a pit required three people.

To enhance transparency and accountability, HUD, Odisha, has made the geolocation of sites mandatory. He also asked district collectors to monitor progress accordingly.

Rainwater harvesting is an essential solution to the emerging water crisis. Human activities have played a major role in the worsening of the climate crisis leading to overconsumption of groundwater and depletion of the water table.

The aquifers, which were used as the main source of fresh water in several places, are not recharged efficiently, resulting in a decrease in the groundwater level. DTE

Opinions expressed are personal


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