Urban Flooding on the Delhi Yamuna: Floodplain Topography and the Limits of Ghat Redevelopment

Urban flooding in India is conventionally attributed to extreme rainfall and inadequate drainage capacity. The July 2023 Yamuna flood in Delhi contradicts that account. The river reached an all-time high flood level (208.66 m) at the Old Railway Bridge while carrying an outflow of only 3.59 lakh cusecs from Hathnikund Barrage — less than half the 8.28 lakh cusecs that produced a peak of just 206.60 m in 2019. This paper contributes a primary topographic dataset from a ground GPS survey of 14,039 points across a 1,105 ha reach of the Yamuna floodplain at Wazirabad, North Delhi. The surveyed terrain is exceptionally flat (71.7% of points within a four-metre band, σ = 2.32 m), so that 41.4% of the reach lay below the 2019 peak and 76.1% below the 2023 HFL. The paper proposes permeability retention as the governing design constraint for ghat redevelopment in this reach.