Datasets for the assessment of changes in the incidence, extents, and spatial patterns of inundations in the Cambodian Mekong Delta, based on a water level - flood link calculated from in-situ water levels, and Sentinel-derived inundation maps.

This brief contains the data needed to calculate and assess the robustness of a water level - flood link (WAFL) in the Cambodian Mekong Delta, which was used to analyze changes in the long-term behavior of Monsoon inundations in the region. The data comprises the WAFL raster (.tif) files for two zones in the delta. Zone A is located on the right bank of the Bassac River, a distributary of the Mekong. Zone B is bracketed between the Mekong River and the Bassac River. The WAFL was calculated by linking water levels measured by the Mekong River Commission (MRC) at the hydrological station in Koh Khel, with inundation maps derived from Sentinel-1 and -2 images taken between 2017 and 2021. The final WAFL raster files provides a basis for estimating inundation extents using in-situ water levels. Furthermore, this brief includes data used for the assessment of WAFL, including in-situ water level data and the extents of natural vegetation in the case study area in 1990, 2000, 2010 and 2020. The former was collected using a differential pressure logger. The latter was calculated from historical Landsat image composites. Finally, raster files representing the incidence and duration of inundations in the case study area before and after the year 2008 are provided. These were calculated based on the WAFL and the MRC water levels. For each area, before- and after-images are available, as well as a raster representing the change between the two. To simplify visualization and geographical location, shapefiles (.shp) of the study area and the location of the in-situ logger are also provided.

Constraining groundwater modeling with magnetic resonance soundings.

Magnetic resonance sounding (MRS) is a noninvasive geophysical method that allows estimating the free water content and transmissivity of aquifers. In this article, the ability of MRS to improve the reliability of a numerical groundwater model is assessed. Thirty-five sites were investigated by MRS over a ∼5000 km(2) domain of the sedimentary Continental Terminal aquifer in SW Niger. Time domain electromagnetic soundings were jointly carried out to estimate the aquifer thickness. A groundwater model was previously built for this section of the aquifer and forced by the outputs from a distributed surface hydrology model, to simulate the observed long-term (1992 to 2003) rise in the water table. Uncertainty analysis had shown that independent estimates of the free water content and transmissivity values of the aquifer would facilitate cross-evaluation of the surface-water and groundwater models. MRS results indicate ranges for permeability (K = 1 × 10(-5) to 3 × 10(-4) m/s) and for free water content (w = 5% to 23% m(3) /m(3) ) narrowed by two orders of magnitude (K) and by ∼50% (w), respectively, compared to the ranges of permeability and specific yield values previously considered. These shorter parameter ranges result in a reduction in the model's equifinality (whereby multiple combinations of model's parameters are able to represent the same observed piezometric levels), allowing a better constrained estimate to be derived for net aquifer recharge (∼22 mm/year).