Hydraulic performance analysis of vetiver grass system for soil and water conservation on steep slope areas | |
| Author | Somchai Donjadee |
| Call Number | AIT Diss. no.WM-08-03 |
| Subject(s) | Vetiver--Research Water conservation--Research Soil conservation--Research |
| Note | A dissertation submitted 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-08-03 |
| Abstract | This research investigated the hydraulic performance of vetiver grass system (VGS) for soil and water conservation on steep slope areas by determining the effects of rainfall intensity, land slope and vetiver hedge interval (VI) in conserving runoff and trapping sediment. The research study involved field experiments with land slopes of 30, 40 and 50% and varying rainfall intensities using an artificial rainfall simulator. The rainfall intensities which were used in the study were 35, 60, 85, 110 and 135 mm h⁻¹. Also, three vertical intervals of 0.75, 1.5 and 3.0 m ofvetiver grass system were used. VGS showed to be an effective management practice to control sediment transport and conserve runoff. In the experiment, the average steady runoff rate corresponded to rainfall intensities with values ranging from 4.7 - 21.4 cm³s⁻¹m⁻² and 1.6 - 15.81 cm³s⁻¹m⁻² for rainfall intensities from 35-135 mm h⁻¹ in control plots and vetiver plots, respectively. Runoff volume also increased with rainfall intensity for both control plots and vetiver plots. The values of runoff volume ranged from 19.7-108.1 mm in control plots and from 5.9 - 68.5 mm in vetiver plots. The narrow VI preserved more runoff volume than the wider VI. However, the values did not vary much among different VIs. Runoff volume had decreased with increasing slope of the control plots. However, land slope did not affect runoff volume in the vetiver plots. The VGS.conserved runoff effectively by 34.4 - 72.0 % as compared with similar plot without VGS. The effectiveness of vetiver grass for trapping sediment reduced when runoff increased due to increase in rainfall intensity. The average steady erosion rates ranged from 1.63 - 49.16 g m⁻² min⁻¹ and 0.30 - 11.09 g m⁻² min⁻¹ for control plots and vetiver plots, respectively. The total soil loss positively correlated with rainfall intensity for both control and vetiver plots. Soil losses were 1.21 - 45.70 t ha⁻¹ on the control plots and 0.22 - 10.00 t ha⁻¹ on the vetiver plots. The results also showed that narrower VI reduced the soil loss more than the wider VI. The soil loss increased more with land slope for both control plots and vetiver plots. The VGS reduced total soil loss by 62.1 - 85.6% compared with the plots without VGS. The percentage reduction in soil loss increased with land slope but, it decreased with increasing VI and runoff volume. The study also developed a general equation for evaluating soil loss under vetiver grass system by using data from previous researches and from measurements done in this study. The equation showed that runoff volume has the highest effect on soil loss, followed by land slope and VI. The MUSLE gives the values of soil loss which were less than observed values. When the MUSS model was used to predict soil loss under vetiver grass system, results indicated that MUSS model prediction is in better agreement with measured values. When rainfall intensity increased, the median sediment grain size (D₅₀) passing through the vetiver strips also increased. The experiment also showed that the land slope and VI had no significant effect on D₅₀. Therefore, the vetiver grass system had a good potential in trapping medium and coarse sediments under steep slopes |
| Year | 2009 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-08-03 |
| 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) | Clemente, Roberto S.; |
| Examination Committee(s) | Athapol Noomhorm ;Tawatchai Tingsanchali ;Chaiyuth Chinnarasri; |
| Scholarship Donor(s) | Royal Thai Government ;Kasetsart University, Thailand; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2009 |