Streamflow and Soil Moisture of Agroforestry and Grass Watersheds in Hilly Area

A study was conducted in a hilly area of Sichuan Province,Southwestern China, to compare the streamflow and soil moisture in two upland watersheds with different land use patterns. One was an agroforestry watershed, which consisted mainly of trees with alder (Alnus cremastogyne Burkill) and cypress (Cupressus funebris Endl.) planted in belts or strips with a coverage of about 46%, and the other was a grassland primarily composed of lalang grass (Imperata cylindrica var. major (Nees) C. E. Hubb.), filamentary clematis (Clematis filamentosa Dunn) and common eulaliopsis (Eulaliopsis binata (Retz.) C. E. Hubb) with a coverage of about 44%. Streamflow measurement with a hydrograph established at the watershed outlet showed that the average annual streamflow per 100 mm rainfall from 1983 to 1992 was 0.36 and 1.08 L s-1 km-2 for the agroforestry watershed and the grass watershed, respectively. This showed that the streamflow of the agroforestry watershed was reduced by 67% when compared to that of the grass watershed. The peak average monthly streamflow in the agroforestry watershed was over 5 times lower than that of the grass watershed and lagged by one month. In addition, the peak streamflow during a typical rainfall event of 38.3 mm in August 1986 was 37% lower in the agroforestry watershed than in the grass watershed. Results of the moisture contents of the soil samples from 3 slope locations (upper, middle and lower slopes) indicated that the agroforestry watershed maintained generally higher soil moisture contents than the grass watershed within 0-20 and 20-80 cm soil depths for the upper slope, especially for the period from May through July. For the other (middle and lower) slopes, soil moisture contents within 20-80 cm depth in the agroforestry watershed was generally lower than those in the grass watershed, particularly in September, revealing that water consumption by trees took place mainly below the plow layer. Therefore, agroforestry land use types might offer a complimentary model for tree-annual crop water utilization.

Classification and Assessment of Freeze-Thaw Erosion in Tibet, China

Based on the analysis of existing relevant research result, a theoretical basis for the defining freeze- thaw erosion zones of Qinghai-Tibet Plateau was been put forward, and a equation for calculating the altitude of the lower bound of the freeze-thaw erosion zones of Qinghai-Tibet Plateau was been established in this paper. Moreover, the freeze-thaw erosion zones in Tibet was been identified by using Geographical Information System (GIS) software. Next, based on the comprehensive analysis of impact factors of freeze-thaw erosion, this paper chooses annul temperature range, slop and vegetation as three indexes, works out the criteria for relative classification of freeze-thaw erosion, and realizes the relative classification of the freeze-thaw erosion in Tibet under the support of GIS software. Then, a synthetic assessment of freeze-thaw erosion in Tibet was been done according to the relative classification result.

Multi-Layer Forecast Project of Rain-Induced Debris Flow

Based on four kinds of methods—numerical weather prediction model, cloud image of stationary meteorological satellite, echo image of meteorological radar and telemetric rain gauge, multi space-time scale precipitation prediction products have been achieved, and multi-layer project of debris flow forecast is established with different space-time scale to get different forecast precision. The forecast system has the advantages in combination of regions and ravines, rational compounding of time and space scale. The project, which has debris flow forecast models of Sichuan province, Liangshan district and single ravine, can forecast debris flow in 3 layers and meets the demand of hazard mitigation in corresponding layer.

Analysis on River Sediment Changes of the Upper Reaches of Yangtze River

The sediment load and river sedimentation of the upper reaches of YangtzeRiver has been undergoing constant changes as complex landform, large mountain area and plentifulprecipitation make the drainage area of Yangtze River very vulnerable to watererosion and gravityerosion. Through analyzing the hydrological and sediment load statistics recorded by majorhydrological stations along Yangtze River since 1950s, and editing the accumulation graph of annualrunoff volume and annual sediment load, wefind out that the suspended-sediment of Yangtze river hasbeen decreasing year by year in Wulong Hydrological Station on Wujiang River, Beibei HydrologicalStation on Jialingjiang River, Lijiawan Hydrological Station on Tuojiang River and GaochangHydrological Station on Minjiang River, Yichang Hydrological Station, Cuntan Hydrological Stationalong Yangtze River mainstream share the same experience too. But the statistics obtained atPingshan Hydrological Station on Jinshajiang River shows the sedimentload there has increased.Taking ecological construction, hydraulic engineering construction and precipitation changes intoconsideration, the thesis analyses the causes for the sediment load decrease of Jialingjiang River,Tuojiang River, Minjiang River and Wujiang River and provides us both scientific foundation forfurther study of river sediment changes of the upper reaches of Yangtze River, and measures tocontrol river sedimentation.