No abstract

The preservation of terrestrial dune field in a tropical region is rare and relies significantly on the degree of weathering process, humidity and anthropogenic condition. In this paper, we report the remnants of sand dunes that is uncovered from Thungkula Ronghai (TKR) dune field in the southern part of the Khorat Plateau, northeastern Thailand. We reveal, for the first time, the results of systematic geomorphological, sedimentological and chronological analyzes of barchanoid ridges and parabolic dunes found on terraces of the Mun and the Chi Rivers. Interpretation in a series of 1952 aerial photographs, satellite images coupled with Ground Penetrating Radar (GPR) survey, and optically stimulated luminescence (OSL) dating were applied. As a result, we found remnants of mega-barchanoid ridges and isolated parabolic dunes varying in height from 1-2 m with maximum length of 4 km, locally distributed in between terraces of the Mun and Chi Rivers, the middle to eastern part of TKR. Dune shapes include lobate, en-echelon and elongate partially overlying on crevasse sand splay, meandered scar, paleo-channel, mid-channel bar of the fluvial depositional sequences. Orientation of all dunes is in NW-SE direction reflecting the formation was due to the prevailing NW monsoon wind. Transition from barchanoid ridge to parabolic dune was observed. Preliminary OSL dating reveals the deposition of sand dunes occurred between 45 to 28 ka. This age range can be inferred to a warmer and drier period occurred in Marine Isotope Stage 3 (MIS3) before the Last Glacial Maximum.

In Southeast Asian countries, flooding is common and occurs a few weeks after tropical storms. In Thailand, the government’s approach to dealing with flooding is focused on the construction of anthropogenic megastructures. The loss of life, property, and ecosystem from flooding still occurs and will likely become increasingly more severe soon due to global climate variation. Here, in this brief report, we show a case study analyzing the cause of unusual flooding that occurred from September to November 2021 during the tropical depression “Dianmu” and the tropical cyclone “Kompasu” that hit the Khorat Plateau, northeastern Thailand. These two tropical storms left behind vast flooded urban and agricultural areas in the upstream part of the Chi River on this, the largest plateau in mainland Southeast Asia. The flood water stagnated for a month and unusually drained downslope in the upstream zone. In this work, a series of free online access satellite images taken by the Sentinel-1 C band GRD and Sentinel-2 available in the Google Earth engine platform was analyzed. As a result, we confirmed that the normal nature of water flow was problematic due to the presence of anthropogenic structures, especially roads. The installation of different design and dimensions of culverts are urgently recommended, particularly in the floodplain zone. The quick responsible idea provided in this paper highlights and simplifies the resilience to future extreme weather events of the rural community and ecosystem.