Predictions of suspended sediment yield in ungauged basins in Thailand | |
| Author | Piyawat Wuttichaikitcharoen |
| Call Number | AIT Diss. no.WM-17-02 |
| Subject(s) | Sediment, Suspended--Thailand--Ungauged basin Erosion--Thailand--Ungauged basin |
| Note | A dissertationsubmitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Water Engineering and Management, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-17-02 |
| Abstract | An estimation of suspended sediment yield is required for engineering practices that deal with improved land and water management practices in a river basin. Similar to other developing Southeast Asian countries, land degradation is a major problem in Thailand. This problem manifests itself in terms of the soil structure and its fertility, in particular for sloping land. The study of erosion and sediment yield has long established itself as an important area of hydrological research due to the economic significance of the processes involved. However, sediment data is rarely available due to lack of monitoring. Erosion and sediment transport are complex phenomena and these processes are affected by several factors such as climatic and geomorphological conditions and land use etc. In Thailand, the study of soil erosion for land conservation planning is mostly based on an empirical Universal Soil Loss Equation (USLE). It is a popular empirical model and has been extensively applied throughout the world to predict soil erosion. However, since soil and rainfall characteristics substantially vary in different regions, these empirical models do not reflect the overall effect of various factors affecting soil erosion. These are lumped models and do not have the ability to describe the spatial variability of soil erosion in a watershed. These days there seems to be a shift in emphasis from empirical modeling to process-based modeling. Although physically-based soil erosion models are widely developed over the last decade, their applications in ungauged basins are still not much due to the huge amount of required data and complexity involved. Climate change has been observed in the past decades, and more changes have been projected for the coming decades. An increase in global temperature is expected to increase evapotranspiration and to cause precipitation changes, which will significantly affect the hydrological regimes of river systems, including streamflow, soil erosion rates, and sediment yield. This study investigates a methodology for using both empirical-based and physically-based erosion and sediment transport models towards better understanding the erosion related processes and develop the methodology for predicting the suspended sediment yields in ungauged basins. The impact of climate change on suspended sediment yield in the study basin was also explored. To achieve the objectives, the study was divided into five parts; the first part involved the analysis of factors influencing suspended sediment yield using principal component analysis (PCA), the second and third parts made estimation of suspended sediment yield using empirical and physically-based modeling approaches (using regression relationships and SWAT model, respectively), the fourth part analyzed the effects of climate change on suspended sediment yield in the study basins, and the final part proposed a methodology for estimating suspended sediment yield in ungauged basins. The study basin covers an area of 102,636 km2 of Ping, Wang, Yom, and Nan River Basins in northern Thailand which are the main tributaries of the Chao Phraya River, the most important river of Thailand. The analysis of factors influencing suspended sediment yield from the PCA with Varimax rotation analysis using the Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy and Bartlett's test of sphericity indicates that there are six components of key factors that can explain at least up to 86.7% of the variation of all suspended sediment related variables. The six components consist of 14 high loading factors, namely total channel length, basin area, main channel length, wet season rainfall, annual rainfall, hierarchical anomaly density, basin slope, relief ratio, basin circularity, agricultural area, forest area, precipitation concentration index, dry season rainfall, and basin elongation. The results of regression models analysis revealed that basin size, channel network characteristics, land use, basin steepness and rainfall distribution are the key factors affecting sediment yield. The validation of regression relationships for estimating suspended sediment yield shows the error of estimation ranging from -55% to +315% and -59% to +259% for suspended sediment yield and for area-specific suspended sediment yield, respectively. Parameters in SWAT model were analyzed for sensitivity on a station to identify the important parameters for runoff and sediment transport. The results showed that GWQMN, RCHRG_DP and CN2 are the top three parameters with the highest sensitivity to runoff. For suspended sediment yield, the parameter USLE _ C has the highest sensitivity followed by USLE _P which is half as sensitive as the top parameter. The usage of the global parameters in ungauged basins was verified with two test stations. The results show that, SWAT model is capable for calculating runoff and sediment transport. The error of estimation in ungauged basins was observed from the PBIAS value which ranges from -21 % to 36% and -91 % to - 122% for flow and suspended sediment estimation respectively. It is applicable for preliminary study for finding model parameters in ungauged basins, when there is no better observed data available. The impact of climate change on suspended sediment yield was assessed at Mae Chaem river basin where data from three GCMs were downscaled and corrected using gamma-gamma and normal-normal methods for rainfall and temperature data respectively. Results show that in most of the cases correlation coefficient (R2), Nash-Sutcliffe efficiency coefficient (NSE) and Percent bias (PBIAS) were improved significantly after bias correction was applied. Study results showed that, in the 30 year future 30 period (2016-2045), the temperature exhibits an increasing trend for both maximum and minimum temperatures by approximately 1°C and rainfall is also expected to increase by 1.97% and 0.65% for RCP4.5 and RCP8.5, respectively. The results also suggest a decrease in total rainfall for the dry season and an increase in the wet season. River flows are expected to increase by 37% and 29% for RCP4.5 and RCP8.5, respectively, while total suspended sediment yields are expected to decrease by 31 % and 36% for RCP4.5 and RCP8.5, respectively. The results of the study provide the knowledge base and reference for suspended sediment assessment for gauged and ungauged basins in Ping, Wang, Yom, and Nan river basins. In addition, the assessment of climate change impacts on sediment yield is also provided for sustainable further watershed management and mitigation plan. The proposed frameworks may be considered useful for predicting suspended sediment yield in ungauged basins of Northern Thailand that have geologic, climatic and hydrologic conditions similar to the study area. |
| Year | 2017 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-17-02 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Babel, Mukand S.; |
| Examination Committee(s) | Sutat Weesakul;Sarawut Ninsawat; |
| Scholarship Donor(s) | Royal Thai Government; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2017 |