关键词: 黄土高原, 侵蚀产沙强度, 时空变化

Abstract:

Based on the distribution of the hydrological station and it's observation series of sediment information on loess Plateau, the study area was divided into 120 hydrological control area firstly, then according to the different soil erosion type area, the 120 hydrological control area were divided into 292 soil erosion units. The main results are as following: (1) The sediment yield of loess plateau (average condition from 1955 to 1989) are mainly come from the violence erosive area with erosion modulus ＞5000t/km².a, the area of it made up 42.8% of the total sediment yielding area, and the sediment from it amounted to 85.0% of the total amount of erosive sediment yield. And the mighty violence erosive area with erosion modulus ＞10000t/km².a, the area of it only made up 18.4% of the total sediment yielding area, but the sediment from it amounted to 50% of the total amount of erosive sediment yield. In the 8 grade of erosion intensity, the sediment yield from the area with erosion modulus2500-15000t/km².a amounted to about 90% of the total amount of erosive sediment yield, and the sediment from the area with erosion modulus 10000-15000t/km².a reach 35.0%. (2) Sediment intensities have changed evidently because of rainfall factor and the effects of soil and water conservation. From the view of structural features of sediment area, the sediment area with erosion modulus ＞10000t/km².a reduced rapidly, from 8.7×104km² (1955-1969)to 2.5×104km² (1970-1989), reduced 71.8%, and the proportion in the total area decreased from 28.2% to 7.9%. And the sediment area with erosion modulus ＞15000t/km².a reduced from 2.9×104km² to 0.6×104km² , reduced 78.3%; the area with erosion modulus ＞20000t/km².a reduced from 1.0×104km² to only 0.2×104km² , reduced 81.0%. In the 8 grade of erosion intensity, the sediment area with erosion modulus ＞20000t/km².a , 15000-20000 t/km².a and 10000-15000 t/km².a decreased greatly , and the reductive degree is 81.0%,76.9% and 68.7% respectively. And from the view of structural features of sediment yield, the proportion of sediment yield of mighty violence erosive area with erosion modulus ＞10000t/km².a in that of total area reduced from 66.0% to 27.8%. And sediment yield reduced more greatly is the area with erosion modulus ＞20000t/km².a , 15000-20000 t/km².a and 10000-15000 t/km².a, the reductive degree is 77.1%, 76.7% and 71.6% respectively. (3) The regions where the sediment yield reduced evidently are mainly distributed in the mighty violence erosive area surrounding Wuding River, and the majority of Fen river, the reductive degree is above 50%. Before soil and water conservation(1955-1969), the regions with erosion modulus ＞10000t/km².a were distributed in the majority of the mainstream reaches of Yellow River between Hekouzheng and Longmen area, the upper reaches of Beiluo River, the most part of upper and middle reaches of Jing River, and the much area of Hulu River and Sandu River in Wei River basin. After soil and water conservation(1970-1989), the regions with erosion modulus ＞10000t/km².a were scattered in Huangpuchuan river, the lower reaches of Kuye River, Jialu River, Wuding River and Qiushui River near to the mainstream reaches of Yellow River, and the riverhead of Beiluo River and Jing River. After control, the area with erosion modulus ＞10000t/km².a in Hekouzheng - Longmen area, the upper reaches of Jing River and Wei River decreased on a large scale, and the erosion modulus reduced to 5000-10000 t/km2.a. the area with ＜5000 t/km².a has changed not too much. (4) The sediment yield of loess plateau, calculated according to tributaries, are mainly come from Hekouzheng - Longmen area (54.8%), next from Jing River (17.6%) and Wei River (13.3%); according to soil erosion type areas, are mainly from loess Mao hill gully region and arid loess hill gully region (50.5%), next from loess Liang hill gully region (11.0%), loess flat hillock hill gully region (9.8%), and loess plateau hill gully region (9.7%); according to soil erosion belts, are mainly from wind and water erosion belt in semi-arid steppe region and water erosion belt in semi-arid forest steppe region (67.4%), next is from water and gravity erosion belt in sub-humid broad-leaf forest region (23.6%). (5) Taking sediment yield intensity ＞10000t/km².a as criterion, there are 7 sediment yield centers on Loess Plateau. The area of the 7 centers made up 15.5% of the total sediment yielding area, however, the sediment yield amounted to 42.1% of the total amount of erosive sediment yield.

Key words: Loess Plateau, sediment yield intensity, time and spatial variation