Rainwater Harvesting: A Solution to Urban Flooding in Karachi | Urban Floods in Karachi 2022

Rainwater harvesting is the process or technology that collects, stores, transports, and purifies rainwater that runs off rooftops, parks, roads, and open spaces, for later use. Rainwater can be collected for various purposes, including non-potable applications such as toilet flushing, irrigation, vehicle washing, and potable applications.

RWH system has the following components:

• Rainwater collection systems are installed on roofs.
• Water is transported using conveyance systems such as gutters, channels, and pipe systems.
• Rainwater storage systems collect rainwater for later use. These are usually tanks, either above or below ground.
• Most potable uses and possibly some non-potable uses will necessitate treatment.
• Filtration is commonly used in rainwater collection and conveyance to remove particulate matter. To control microbial growth in various systems, including storage systems, simple disinfection (chlorination, ultraviolet - UV, solar) may be required.
• The distribution of stored water to its intended use may necessitate using a system of pumps, pipes, and controls.

FLOODING IN KARACHI 2022

Karachi has been troubled by severe floods for many years due to a lack of planning. The rainfall again proved to be disastrous for the city this year, as it had been in previous years. The ferocious rains turned into a nightmare, flooding homes and underpasses, knocking down towers and power lines, and cutting off communications for many in the city of lights.

REASONS FOR FLOODING IN KARACHI

When heavy rains cause flooding and devastation in Pakistani cities, governments blame climate change. But is it the result of climate change or poor planning? Karachi's stormwater drains (nullas) are two seasonal rivers, the Lyari and the Malir. Both begin in the Kirthar range's foothills and run parallel for 14-20 kilometers. More than 600 smaller drains connect to 58 stormwater drains (or nullas) that transport water from catchment areas. Following are some of the reasons for flooding in Karachi:

• The heavy concretization of the city is a critical and alarming factor among the various causes of urban flooding in Karachi. Public and open spaces are disappearing, and concrete has replaced them, causing water to accumulate.
• Karachi is a large city with only two landfill sites, both of which are located more than 40 kilometers east of the city. Garbage does not reach landfill sites due to the high time and monetary costs of using these. Meanwhile, the recycling industry expanded, especially in the informal sector. Contractors pay KMC officials to collect recyclable materials instead of picking up garbage. Non-recyclable waste is then disposed of in nullahs or at a variety of informal dumping sites that are linked to natural drainage systems.
• The drainages have been encroached upon in such a way that their endpoints are blocked, even though they should drain into the sea. Because the small amount of water that comes in is not discharged into the sea, flooding.
• The primary cause of urban flooding is the city's haphazard planning. Transportation and road construction are examples of infrastructure development, but drainage is not. Roads are built end to end because there is no concept of service roads. There is no drainage infrastructure in addition to road and transportation infrastructure. A lack of coordination between departments is one of the causes of failed planning. One department constructs the road, while another demolishes it.

IMPORTANCE OF RWH FOR KARACHI

Rainwater is a clean water source that is frequently superior to groundwater or water from rivers or lakes. In some countries, RWH is required by law for every household. It is used to provide drinking water, domestic water, water for livestock and small irrigation, and to replenish groundwater levels in China, Argentina, and Brazil.

If we talk about Pakistan, several RWH projects have been completed and are operational. Following the 2005 earthquake, the Earthquake Reconstruction and Regulation Authority Water and Sanitation (WatSan) installed approximately 12000 RWH Systems in school buildings, houses, and hospitals throughout 20 Union Councils in AJ&K and KPK. Furthermore, the organization has taken steps to require RWH in all new buildings. The system provides a simple and easy method for collecting, managing, and effectively utilizing rainwater at a low cost. In the earthquake-affected areas, the project was a success.

In Karachi, most of the rainwater that floods the roads eventually seeps down into the water table. We can make natural dams in areas with a depression to store rainwater. This can be done without any government intervention as well. All you need to do is place a mesh that can act as a filter to ensure garbage doesn't go into any storage facility.

RWH: A CASE STUDY OF LAHORE

The Punjab government did a successful experiment with rainwater harvesting i.e., the Underground Water Storage Tank at Lawrence Road. The project area is low-lying having depressions which was the ultimate cause of ponding. The highest ground level in the project area is 216 m while the lowest ground level is 211 m. Due to this elevation difference water used to get accumulated in the area near Lawrence Garden and the Board of Intermediate & Secondary education (B.I.S.E), Lahore has a depressed ground level which in turn results in ponding.

The project catchment area is 30 acres, and the ponding area is 3 acres. China Chowk, the Board of Intermediate and Secondary Education (BISE) Lahore building, examination halls, the Lahore Zoo, Lawrence Garden, the Lahore Chamber of Commerce & Industry building, Sir Ganga Ram Hospital, and the chairing cross are all within walking distance of the project catchment area. The Bagh-e-Jinnah, formerly known as Lawrence Gardens, is a historical park in the Pakistani city of Lahore.

The project structures are constructed in the parking area of the open area theatre. After the construction of the structures, the parking area was restored to its original status with certain improvements i.e., the addition of a tennis court for healthy activities. No trees, plants, etc. were cut for the construction of structures but more plantation was carried out to make the location environment friendly. The stored rainwater in the underground tanks is aimed to be utilized for horticulture and drinking purposes after purification. The project aims to promote an efficient and effective drainage system for the city's strengthening stormwater management system.

CONCLUSION

RWH is a simple and low-cost solution to Pakistan's growing water problems, as underground water resources deplete and demand for water rises due to population growth. Despite varying degrees of complexity, the systems are generally low-cost and easy to implement. The water that has been stored can be used for a variety of purposes, including domestic, agricultural, and human consumption.