Jeevesh Gupta
DELHI IS AN URBAN space totally gone wrong, with a population of around 20 million, way beyond its capacity. If we go downstream of the Wazirabad barrage, a series of 21 drains flows into the Yamuna, making it a giant drain. The city generates more than 3 million cubic metres of treated and untreated sewage.
The total mean annual flow for the Yamuna up to the Delhi stretch is 12-13 thousand million cubic metre (TMCM). The water abstraction from the river for irrigation and drinking till Delhi is about 10-11 TMCM. This leaves only a free river flow of about 2-3 TMCM. For the Yamuna, as for most Indian rivers, around 80 per cent of the flow occurs in the monsoon months (July to September) and the rest in the nine non-monsoon months. There is almost zero environmental flow available downstream of Wazirabad barrage during the non-monsoon months.
Haryana releases 10 cumecs (cubic meters per sec) of flow at Hathanikund during the lean season. However, most of it evaporates or percolates before it reaches Wazirabad.
Even if the Delhi Jal Board (DJB) treats the entire sewage generated in Delhi up to the biochemical oxygen demand (BOD) of 10 mg/l, the desired water quality, which is BOD less than 3 mg/l and dissolved oxygen of over 5 mg/l, may not be achieved due to the unavailability of fresh water in the river downstream of Wazirabad. The annual average BOD in the Yamuna varies from 11 to 24 mg/l. That is, the average non-monsoon season BOD level is close to eight times more than the desirable level. This would require a dilution of eight times to make it fall into safe health limits or a freshwater flow of over 20 MCM per day. Clearly, during the monsoon months, there is adequate dilution flow to maintain health standards. But during the non-monsoon months, this is not possible. Therefore, in the non-monsoon months, there is no option but to treat the sewage of Delhi and reduce the BOD to no more than 5 mg/l. Thus, Yamuna needs comprehensive cleansing of sewage.
There is also the issue of algal choking. To avoid still-water algae growth, a minimum flow velocity of 0.75 m/s is required. The non-monsoon flow needed to do this is estimated to be 1.8 TMCM, whereas the Yamuna's current total non-monsoon flow is just 0.44 TMCM, which is leading to algal choking of the river, causing oxygen depletion and addition of toxins produced by algae.
While the issue is mounting, there are solutions in sight, such as a flow of 23 cumecs in the lean season recommended by the National Institute of Hydrology in its study report submitted to the ministry of jal shakti. While this looks like a plausible solution, the dam projects upstream are still a few years away. The water stored can be sent downstream during the lean season, and the flow can be increased subsequently.
Then there is water harvesting and introducing more efficient agricultural practices like drip irrigation, and shifting water-intensive agriculture (for example, rice and sugarcane) to water-surplus areas.
The pumping of groundwater by borewells in the Yamuna flood plains, especially by the Delhi Jal Board, also has an impact on the river base flow in the lean season. This pumping should be reduced, and water shortage should be covered by increasing the number and efficiency of rainwater harvesting pits across the NCR region.
Most importantly, the entire sewage generated from the stretch of Delhi requires treatment through sewage treatment plants and common effluent treatment plants in Haryana, Delhi and Uttar Pradesh. Upgrading existing sewage treatment plants and their efficient running is a big challenge, which has not happened despite environmentalists demanding it for decades. Promoting organic farming and reducing the use of fertilisers by agriculturists farming in the Yamuna plains will also go a
long way.
Jeevesh Gupta is an environmentalist and co-author of the book Green Day.