Reservoir characteristics are the essential information for water management planning and reservoir operation. Regular monitoring and assessment of the reservoir characteristics can reduce risks associated with the reservoir operation. This research assessed the reservoir characteristics (water surface, volume) of Vajiralongkorn Dam using remote sensing. Reservoir water surface was classified using the Normalized Difference Water Index (NDWI) derived from the Landsat 8 data, and validated using the streamline matching rate (SMR) and the streamline matching error (SME) techniques for shoreline accuracy assessment. The volume between two water levels was calculated using the prismatic equation. The storage capacity curve was constructed from the reservoir water level and cumulative volume. The accuracy of NDWI technique was satisfactory in identifying reservoir water surface with a good accuracy of shoreline delineation (SMR>95% and SME=11.7 m). The water surface has decreased on the average of 8.2 km 2 (2.8%) compared with the original data in 1980. The storage capacity has decreased 495.3 million m 3 (MCM) over 38 years from 1980 to 2018, an annual capacity loss of 13 MCM. Finally, sustainable service of the reservoir needs better knowledge of the effects of storage loss, the erosion and sediment-transport processes, and conservation measures.
Seawater intrusion associated with climate change and sea level rise (SLR) has been postulated for the last decade that causes negative impact on worldwide environmental resources. In Thailand, however; the pertaining information to its effect on soil properties in agricultural areas has not been clearly reported yet. Hence, this study aimed to investigate the seawater intrusion effect on soil properties in agricultural areas of Nonthaburi Province, Thailand. Five study locations, which anticipated to be affected by seawater intrusion, were selected based on the different distances from the Chao Phraya River. Soil morphological properties at depth of 0-15 and 15-30 cm were recorded, besides disturbed soil samples at depth of 0-15, 15-30, 30-60, 60-90 and 90-120 cm were collected to determine the soil physical and chemical properties. Additionally, the soil electrical conductivity (ECe) and sodium adsorption ratio (SAR) analyses demonstrating soil salinity and sodicity were monthly conducted from March 2018 to February 2019 and their annual average values were calculated. The results revealed that all soils were deep to very deep, consisted of silty clay, clay textures, and its field soil pH varied from 6.0-8.0. Soil saturated hydraulic conductivity rating exhibited that it was very slow to moderate. ECe and SAR values of these soils ranged from 0.21-4.38 dS m-1 and 8.29-41.89 consecutively, which trended to increase from its annual average during March and April 2019 as well as July and August 2019. These results suggested that seawater intrusion could be presumptively regarded as a co-factor affecting the variability of soil salinity and sodicity occurring at the interval of insufficient freshwater content for forcing seawater. The implementation strategies for freshwater management and planning are required to prevent future potential seawater intrusion.
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