Piyatida Ruangrassamee

The large-scale monitoring of riverbank erosion is challenging because of human, equipment, and financial limitations, particularly in developing countries. This study aims to detect riverbank erosion and identify riverbank erosion hotspots along the Mekong River in Cambodia. A riverbank erosion rate map was developed using satellite images from Landsat 5, 7, and 8 (1990–2020) using the modified normalized difference water index (MNDWI) at a resolution of 30 m and Sentinel-2 (2016–2021) using the normalized difference water index (NDWI) at a resolution of 10 m. Detecting riverbanks in satellite images using a water index depends greatly on image resolution and water threshold. The riverbank lines were validated using Google Earth images. In the data used in December 2017, the root mean square error (RMSE) of Sentinel-2 was 6.00 m, while the RMSE of Landsat was 6.04 m. In the data used in January 2019, the RMSE of Sentinel-2 was 4.12 m, while the RMSE of Landsat was 5.90 m. The hotspots were identified by overlaying the riverbank erosion rate map and the exposure map of population density and land cover. Field surveys and interviews were conducted to verify riverbank erosion hotspots in the Ruessei Srok and Kaoh Soutin communes. The results showed that within the last 30 years (1990–2020), the riverbank eroded more than 1 km in a direction perpendicular to the river in some segments of the Mekong River in Cambodia. The highest average annual erosion rate was in the Ruessei Srok Commune in Kampong Cham Province, at approximately 43 m/yr. Most eroded areas were farmland and rural residential areas. The riverbank hotspots are situated mainly in the lower part of the Mekong River, where the population is dense, and the erosion rate is high. Riverbank erosion hotspots with a very high impact level and ongoing active erosion include the Peam Kaoh Sna, Kampong Reab, Kaoh Soutin, and Ruessei Srok communes in Kampong Cham Province. This study provides an efficient tool for using satellite images to identify riverbank erosion hotpots in a large river basin. The riverbank erosion hotspot map is essential for decision-makers to prioritize interventions to reduce the risk of riverbank erosion and to improve the livelihood of the people residing along the Mekong River.

Financial feasibility is usually a concern in water reclamation projects. Aside from internal benefits, water reclamation in industrial parks delivers health and environmental benefits not normally considered in cost–benefit analyses (CBA). This study investigated the influence of environmental benefits on the feasibility of water reclamation projects with flow rate scenarios in accordance with industrial parks in Chonburi, Thailand. CBAs of water reclamation plants for industrial water supply, consisting of ultrafiltration (UF) and reverse osmosis (RO), with flow rates of 5200, 10,000, 15,000, and 25,000 m³/day and discount rates of 3%, 5%, 7%, 9% and 11% were conducted. Considering only the direct costs and benefits, none of the projects were financially feasible. However, when the environmental benefits were included, the projects became profitable in all cases except those with a flow rate of 5200 m³/day and discount rates of 5%, 7%, 9%, and 11% and those with flow rates of 10,000 and 25,000 m³/day and an 11% discount rate. Further, CBAs of water reclamation projects in industrial parks for irrigation were conducted with post-treatment processes consisting of sand filtration and chlorine disinfection for flow rates of 240, 480, 2400, 3600, and 4800 m³/day. The projects are profitable, regardless of environmental benefits.

Nan River Basin contributes about 25 to 40 percent of annual flows in the Lower Chao Phraya River Basin, Thailand. Land use and climate change result in change in meteorological and hydrological conditions in Nan River Basin. In addition, water demand in the basin has been increasing from the economic development. Understanding cross-sectoral interactions from both water resources and economic points of view provides better insight in planning and management. This study proposes an integrated framework of hydrological and economic analysis to assess impacts of water deficits under changing climate and regional development. The objectives of the study are to analyze water supply under climate change scenarios, estimate water demand under economic development scenarios, and assess cross-sectoral impacts of water deficits. A rainfall-runoff model, integrated flood analysis system (IFAS), was calibrated, verified, and used to simulate runoff. Regional input-output model was developed for Nan River Basin to assess economic impacts of water deficits. Analysis of water deficits under climate change scenarios and economic development scenarios was carried out during the period of 2040-2059. Runoff simulations under climate change scenarios using two GCMs, IPSL-CM5A-MR and MIROC5 under RCP4.5 and RCP8.5 showed increasing trend. Water demand projections of all sectors also showed increasing trend especially in agricultural sector. The uncertainty of water supply under the climate change scenarios is found to be relatively small compare to the uncertainty of water demand under the economic development scenarios. Assessment of indirect economic loss from cross-sectoral analysis is found to be two to three times higher than the direct loss. The results demonstrate the need to consider the indirect economic loss across sectors in water allocation planning and water deficit mitigation policy.

Nan River Basin contributes about 25 to 40 percent of annual flows in the Lower Chao Phraya River Basin where main agricultural, manufacturing, service, and domestic water use sectors located. Water allocation during dry season depends mainly on the amount of water storage at the end of rainy season in the four main reservoirs in the upstream of the Chao Phraya River. However, impacts across sectors are also important in developing strategies to mitigate drought. Understanding cross-sectoral interactions from both water resources and economic point of view provide better insight in decision making. This study proposes a framework of cross-sectoral analysis of water allocation during dry season between three sectors (agriculture, manufacturing, and service and domestic) in the Nan River Basin with the consideration of impacts to the Lower Chao Phraya River Basin. An assessment model in this study is based on the water budget and the Input-Output model. Preliminary results of economic analysis of cross-sectoral impacts of water allocation in the Nan River Basin show the importance of considering interactions between sectors and non-hydrologic factors in developing strategies to mitigate droughts.

Groundwater is one of the important sources of water supply in Thailand especially in non-irrigated areas during dry season. Numerous groundwater contaminated sites have been reported from both natural and anthropogenic (i.e., man-made) activities with extent of plume migration, leading to a degrading quality of groundwater which is unacceptable for human consumption. Determination of contaminant transport parameters in the saturated zone is of great importance for groundwater risk assessment. For our study, a series of column experiments were conducted to obtain the transport parameters of 2-nitrophenol in natural soil which are collected from a contaminated site in Thailand. 26 porous media samples were randomly collected from the site from 1.5 m depth below ground surface and further analyzed for their grain size distribution using ASTM D422-63 standard method (standard test method for particle-size analysis of soils) to cluster the sample. Upward flow direction column setup was employed with 23.7 mM phosphate buffer containing 10 mg/L NaCl solution (as a conservative tracer) influent for at least five pore volumes (PV) at 30 mL/h constant rate injection, then switched to 10 mg/L of 2-nitrophenol in 23.7 mM phosphate buffer solution and the column was consecutively flushed for another 5 PVs. Effluents were systematically collected in every 0.25 PV and further analyzed for their Cl- and 2-nitrophenol contents by using a well-calibrated conductivity meter and gas chromatograph (GC), respectively. Natural soil from the study area could be clustered into three groups based on their D₅₀ values of 0.16 mm, 0.27 mm, and 1.08 mm, respectively. Cl- and 2-nitrophenol breakthrough curves were plotted and compared to assess the contaminant transport parameters, including its dispersivity and retardation factor in comparison to the conservative tracer. The dispersivity of 2-nitrophenol for three groups of sample is 0.41 cm, 0.34 cm, and 0.35 cm, respectively. For retardation factor, they were equal to 1.127, 1.086, and 1.086, respectively.