Ismail Mondal, Sajad Ali, Mukhiddin Juliev, Lal Mohammad, Mohammed A Almalki, Mohammad Alfredan
Flood-related water-quality change and ecological stress are closely coupled in deltaic rivers, yet they are seldom integrated within a single management framework. This study presents a management-oriented flood-water-quality and ecological-risk screening framework for the Ichamati River, based on 36 in-situ observations collected at 12 upstream, midstream, and downstream monitoring sites during the pre-monsoon, monsoon, and post-monsoon campaigns in 2025. Water temperature, dissolved oxygen (DO), pH, and salinity ranged from 31.55 to 35.00 °C, 7.65-12.89 mg L-1, 8.08-9.35, and 0.010-0.050 psu, respectively. Concurrent depth, velocity, and discharge proxy (Qproxy) measurements were integrated with Landsat-8 observations, principal component analysis (PCA), locally estimated scatterplot smoothing (LOESS), Random Forest (RF), and explainable machine learning (ML). The first two principal components explained 65.86% of hydrochemical variability, while a dimensionless seasonal hydro-constituent synthesis represented pre-monsoon accumulation and rainfall-triggered mobilisation, monsoon dilution and advective flushing, and post-monsoon retention and delayed release. RF model testing yielded R2 = 0.91, RMSE = 0.12, and MAE = 0.09, with DO stress contributing 28.6%, temperature stress 22.1%, hydraulic exposure 19.9%, pH deviation 16.7%, and salinity stress 12.7%. Very High and High classes accounted for 23.6% and 25.8% of the flood-water-quality assessment, and 17.5% and 24.3% of the ecological-risk assessment. Their strong association (r = 0.82; R2 = 0.68) identified downstream tidal reaches as integrated intervention priorities. The framework supports seasonal source control, monsoon transport surveillance, post-monsoon recovery assessment, ecological restoration, and strategic sensor deployment, providing a robust scientific basis for climate-resilient river management.