Flood risk assessment and protection measures in the Nura River basin, Kazakhstan

Abstract

Spring floods represent one of the major natural hazards in snowmelt-dominated river basins of Central Asia. The Nura River basin in Central Kazakhstan is particularly vulnerable because of pronounced interannual runoff variability, limited reservoir regulation capacity, and the hydraulic connection between the Nura and Ishim river systems. This study aimed to provide an integrated basin-scale assessment of spring flood hazards and to identify key hydraulic constraints relevant to flood-risk management. The assessment was based on long-term hydrological observations covering periods of up to approximately 90 years. Extreme spring flood discharges and runoff volumes were estimated using the Kritsky–Menkel frequency-analysis method based on a three-parameter gamma distribution. The analysis was supplemented by assessment of reservoir storage capacities, floodplain topography, channel conveyance, and the Nura–Ishim bifurcation zone using cartographic, digital elevation, and engineering data. The adopted probability distribution was additionally evaluated against alternative flood-frequency models using goodness-of-fit and information criteria. For a 1% exceedance probability, the estimated maximum spring discharges were 752 m 3 /s at Sheshenkara, 1220 m 3 /s at Sergiopolskoye, and 2360 m 3 /s at Romanovskoye. The corresponding 1% spring flood volumes reacheNura River and the distributary system of the Nura–Ishim interfluve may begin at approximately 800 m 3 /s, with an estimated plausible range of 750–850 m 3 /s. The interfluve can store approximately 400 million m 3 of floodwater, whereas extreme inflow may reach about 350 million m 3 per day, compared with a downstream Ishimestimated plausible range of 750–850 m 3 /s. The interfluve can store approximately 400 million m 3 of floodwater, whereas extreme inflow may reach about 350 million m 3 per day, compared with a downstream Ishim conveyance capacity of approximately 100–150 million m 3 per day. The results demonstrate that extreme spring flood volumes cannot be managed effectively by reservoir regulation alone and that the Nura–Ishim interfluve plays a critical role in floodwater redistribution. Comparison with Austrian flood-risk management practice supports a transition from localized protection toward integrated basin-scale management combining structural measures, controlled retention areas, and spatial planning. The proposed measures include earth embankments with controlled overflow sections, riprap bank protection, and mobile water-filled barriers. auseuse the analysis combines pre- and post-regulation hydrological records and does not include formal non-stationary frequency analysis or detailed two-dimensional hydraulic modeling, the estimates should be interpreted as basin-scale planning values rather than precise local inundation predictions. The findings provide a quantitative basis for strategic flood-risk management and infrastructure resilience in snowmelt-dominated river systems of Central Asia.