How flood-prepared is Delhi? Govt shares its plan with NGT

After the committee submitted a report August 28, 2024, the I&FCD – nodal agency for desilting works in the Capital – had taken over the maintenance of all drains flowing into water bodies, including the Yamuna.

The department placed before NGT findings of a study on the discharge carrying capacity of the Yamuna up to the Delhi border. According to the report, one-dimensional water profile simulations was undertaken by the Central Water Commission (CWC) by using the HEC-RAS model – a system that simulates flow through a network of open channels, both artificial and natural – based on surveyed cross-sections from the Hathnikund barrage to the Delhi-Haryana border over a 202-km stretch.

However, the study noted that limited cross-sectional data provided by the Haryana Irrigation department resulted in “erratic” outputs, and the model has been shared with Haryana authorities for refinement and validation to arrive at realistic carrying capacities.

The carrying capacity across various divisions along the stretch was found to vary widely – from about 1,000 cumecs in parts of the Karnal division to 30,000 cumecs in certain reaches of the Delhi division. The report also noted that embankments exist at some locations for flood protection, while overflow beyond riverbanks during heavy floods is managed by Haryana authorities.
The timeline to refine this study will be provided by the Haryana Irrigation and Water Resources department, I&FCD told NGT.

In regard to long-term flood management measures, the department said a “scientific assessment of River Yamuna by application of hybrid model” has been assigned to the Central Water and Power Research Station (CWPRS), Pune. The report is expected by August, after which further measures will be finalised, it added.

The department further said that as mandated by NGT for floodplain demarcation, CWPRS is also preparing a map based on the 1:100 year highest flood level with 1 meter contour – a regulatory standard used to demarcate floodplains, representing a flood with a 1% annual probability of occurrence. This is expected to be completed by August 31, it added.

Further, the department said that following the committee’s recommendations, short-term measures to adapt “structural measures to avoid flooding…” have already been taken. “…work of raising the level of right bank consisting of area of ORB and Nili Chatri… is expected to be completed before next monsoon season,” it said, adding that work along embankment from Hathi Ghat to drain 12 regulator “has been completed and in operation”.

The department also informed NGT that modern discharge measurement systems, including SCADA-based monitoring at barrages and drains, are either being installed or upgraded. Under SCADA (Supervisory Control and Data Acquisition) systems, computer-based platforms work on real-time monitoring and data acquisition at barrages and drains.

Gauges along the river and drains are being marked with GTS benchmarks ahead of monsoon, the NGT was told. GTS (Great Trigonometrical Survey) benchmarks are fixed survey points established across India to indicate precise elevation relative to the mean sea level while mapping work is undertaken.

Moreover, to address coordination gaps among agencies responsible for drains in Delhi, the government has constituted an Inter-Departmental Monitoring Committee (IDMC) headed by the Chief Secretary to ensure seamless work, the submission stated.

The NGT was further told that of the drains flowing into water bodies, 14 already have regulators in place to control flood based on defined operating protocols while regulators for the rest are being installed.