Geomorphological change of the upper Yom river in Phrae province

Abstract

Yom River is the main tributary of the Chao Phraya River; the upper Yom River flows through Phrae Province. This research selected the upper Yom River because of meander processing in an active basin, which rapidly migrates and changes landforms all the time, The object of this research is to study geomorphological change, thickness and behavior of the upper Yom River in Phrae Province.

By assessing aerial photographs and satellite images from 1954 to 2019, the researchers were able to interpret the geological changes that occurred over the past 65 years. The study identified several geomorphological changes from channel migration which can be obvious on maps. The upper and middle sections of the research site, characterized by a flat and wider floodplain area, exhibited more remnants of cut-offs compared to the lower section. To compare the changes, five geomorphic criteria were used: channel width (W), channel length (L), sinuosity index (SI), radius of curvature (Rc), and channel migrations. The width (W) underwent significant alterations due to increased bank deposition resulting from human activities and deforestation. Changes in land use were found to have various impacts on runoff and sediment supply. The channel's length and sinuosity index (SI) showed a decreasing trend, indicating frequent cut-offs at the neck and chute during floods. Erosion rates were observed to be lower in the upper and middle parts of the Yom River due to previous cut-offs, while the lower portion exhibited active bending as evidenced by migration rates versus Rc/W values. Lower Rc/W values corresponded to slower rates of bend migration.

The sedimentology and geophysics field investigation from different landforms. Grain size analysis revealed sediment types including mud, sandy mud, muddy sand, sand, gravelly sand, and sandy gravel in point bars and paleo-channels, and mud and sandy mud in floodplains and meander scars. ERT and GPR analyses provided insights into the lithological characteristics of the study area. The ERT profiles displayed visible vertical and horizontal changes in fluvial deposits, which ranged in thickness from 5 to 20 meters, similar to the floodplain, point bar, and paleo-channel. Additionally, five types of radar facies were observed in river deposits: Continuous (Parallel), Inclined, Concaved-up (Channel fill), Chaotic, and Reflection Free.

This study's comprehensive analysis of various data sources and techniques shed light on the geomorphological changes that have occurred in the upper Yom River over the past decades. The findings also contribute to our understanding of the Yom River behaviors, landform evolution, the sediments and the paleochannels' thickness.