An experimental campaign was set up to quantify the contribution of evapotranspiration fluxes on hillslope hydrology and stability for different forest vegetation cover types. Three adjacent hillslopes, respectively, covered by hardwood, softwood, and grass were instrumented with nine access tubes each to monitor soil water dynamics at the three depths of 30, 60, and 100 cm, using a PR2/6 profile probe (Delta-T Devices Ltd) for about 6 months including wet periods. Soil was drier under softwood and wetter under grass at all the three depths during most of the monitoring period. Matric suction derived via the soil moisture measurements was more responsive to changes in the atmospheric conditions and also recovered faster at the 30 cm depth. Results showed no significant differences between mean matric suction under hardwood (101.6 kPa) with that under either softwood or grass cover. However, a significant difference was found between mean matric suction under softwood (137.5 kPa) and grass (84.3 kPa). Results revealed that, during the wettest period, the hydrological effects from all three vegetation covers were substantial at the 30 cm depth, whereas the contribution from grass cover at 60 cm (2.0 kPa) and 100 cm (1.1 kPa) depths and from hardwood trees at 100 cm depth (1.2 kPa) was negligible. It is surmised that potential instability would have occurred at these larger depths along hillslopes where shallow hillslope failures are most likely to occur in the region. The hydrological effects from softwood trees, 8.1 and 3.9 kPa, were significant as the corresponding factor of safety values showed stable conditions at both depths of 60 and 100 cm, respectively. Therefore, the considerable hydrological reinforcing effects from softwood trees to the 100 cm depth suggest that a hillslope stability analysis would show that hillslopes with softwood trees will be stable even during the wet season.
|Original language||English (US)|
|Number of pages||14|
|State||Published - Jul 30 2018|
Bibliographical noteFunding Information:
This research was supported by the University of Tehran under Grant 3591874. The effort of J. L. Nieber on this project was partially supported by the USDA National Institute of Food and Agriculture, Hatch/Multistate Project 12‐059. This work was also supported by the University of Minnesota during the data analysis and processing. Gratitude is expressed to Mr Moharramali Nazarirad, Mohsen Gorgandi, Fatollah Ghomi, Rahmat Ghomi, Nour Ali Samarghandi, and Ghodrat Daneshvar for their valuable assistance during experimental set‐up and measurements. We also thank Mr M. T. Tirgarsoltani and Mr Asadollahi for their assistance in soil labs. Dr Bruce Wilson's and Ehsan Ghane's support during statistical analysis and Dr Diana Karwan's and Dr Andrew Simon's constructive comments are much appreciated.
© 2018 John Wiley & Sons, Ltd.
- forested hillslope hydrology
- hillslope stability
- matric suction
- soil water content