The Reservoir Sedimentation Volume And Its Function To Sedimentation In Region Of Helong Reaches Of Yellow River

The issues of reservoir sedimentation is affected the ecological and economic benefits for reservoir, so the reservoir sedimentation study has important practical applications. In recent year, the issues of the water and sediment dropped for Yellow River has caused widespread concern by the public, research studies for water and sediment reduction of water and sediment conservation measures was carried out, for example research the sediment reduction of Check dam, Terraced, Grass and climatic to the reduction of Yellow River sediment load ratio, in order to probe the reason of the reduction of Yellow River sediment load, but currently little research was aimed at the problem of the reservoir sedimentation, in particular,research for reservoir siltation problem on a region and the estimation for no monitoring reservoir siltation was less. This paper used a variety of mathematical statistics such as Mann-Kendall test method and Double accumulative curve, et al to research the runoff, sediment and the reservoir sedimentation on Helong Region, to analysis the change rule of the runoff and the sediment as well as the siltation rule of the reservoir, to calculated the water and sediment reduction by human activity and estimated the total reservoir sedimentation volume, so as to quantitative evaluation the function of sedimentation reduction in Region of Helong Reaches of Yellow River. In order to provide an important reference to the efficient use of reservoirs in the region and provider a scientific basis for comprehensive management of water and sediment of Yellow River, it has important scientific significance. The main conclusions are:(1) Annual rainfall on Helong region shows a slow downward trend from 1957 to 2012, declined by an average annual rainfall of 1.38 mm, the distribution of the space is gradually decreases from southeast to northwest; The runoff and sediment yield on Helong region were showed a decreasing trend from 1950 to 2012, decreased by approximately 0.99×108m3 and 0.17×108t per year; The runoff and sediment load on Helong region were suddenly changed in around 1970 s and 1990 s, from these two year on, both fall trend were significantly enhanced.(2)The runoff during the year on the Helong regionwere were concentrated in July to October, the change of runoff on each tributary shows a downward trend, of which the largest decrease runoff per nuit area is Kuye river, is 6.18×104 m3/km2·a, while the minimum is Yanhe River Basin, is 3.41×104m3/km2·a; the sediment load distribution during the year were concentrated in July to October, the sum of sediment load on that four months accounted for more than half of the total annual sediment load, the change of sediment load on each tributary shows a downward trend, of which the largest decrease runoff per nuit area is Huangfuchuan river, is 1.27×104t/km2·a, while the minimum is Wuding River, is 0.35×104t/km2·a.(3) Comprehensive analysis the relation between the runoff, sediment discharge and rainfall, analyze and calculate the atarting year for reduce runoff and sediment load by human activity and calculate the runoff and sediment reduction by human activity. The influence of starting year on Helong region is 1974, due to the impact of human activities, the reduction of runoff on Helong region is 905.06×108m3 from 1975 to 2012, the average annual reduction is 23.21×108m3; sediment load was reduced 179.75×108t from 1975 to 2012 and the average annual reduction is 4.73×108t, the amount of sedimention on 2012 is 10.04×108t.(4)The reservoirs on Helong region were constructed uneven distribution of time and space, from 19556 to 2012, 1970 s is the peak of reservoir built, the total number of reservoir built is 134, accounting for 65% of the total number of reservoir, with a total capacity of 17.53×108m3; the spatial distribution of reservoir were concentrated in several major tributaries, which the medium-sized reservoirs were focused on Wuding river basin(the number is 26), the small reservoirs mainly in Wuding river basin(the number is 67), Hong river basin(the number is 19), Huangfuchuan basin(the number is 16) and the Kuye river basin(the number is 10).(5)The siltation features for reservoir on different modulus of sediment yield have different deposition characteristics, divided the middle and small reservoir on Helong region into five types based on sediment yield: micro-eroded area(the sediment modulus is 0-2000t/km2·a), mild-eroded area(the sediment modulus is 2000-10000t/km2·a), moderate-eroded area(the sediment modulus is 10000-15000 t/km2·a), severe-eroded area(the sediment modulus is 15000-20000t/km2·a) and strong-eroded area(the sediment modulus is more than 20000t/km2·a), the deposition characteristics of reservoir on different types area are as fllows: the capacity loss rate for reservoir on micro-eroded area were remained unchanged from 1990 s, and the average loss rate was negative linear correlation with the reservoir construction time; the capacity loss rate for reservoir on mild-eroded area, moderate-eroded area after 1970 s, severe-eroded area and strong-eroded area after 2000 were logarithmic correlation with the number of years used, and reservoir on bigger sediment modulus its capacity was larger; the capacity loss rate for reservoir on moderate-eroded area before 1970 s and strong-eroded area before 2000 were remained unchanged and the capacity were kept 0.834 and 0.7755.(6)Based on data about the siltation and the deposition characteristics for medium-sized and small reservoir on Helong region, combined with the sedimention reduction by human activity, quantitative evaluation the proportion of sedimentation reduction by reservoir sedimentation to the total amount of sediment reduction in Region of Helong Reaches of Yellow River. The total amount of reservoir sedimentation was 15.14×108m3 until 2011, and the larger reservoir was deposited 6.22×108m3, about 8.08×108t, the middle reservoir was deposited 7.40×108m3, about 9.62×108t, the small reservoir was deposited 1.52×108m3, about 1.95×108t, the reservoir sedimentation volume on Helong region were account for 11.58 of the total sediment reduction by human activity, and the larger reservoir account for 4.76; medium-sized reservoirs had a share of 5.67%; small reservoir that the proportion accounted for 1.15%.