第 26 卷 第 2 期 农 业 工 程 学 报 Vol.26 No.2 64 2010 年 2 月 Transactions of the CSAE Feb. 2010

Effects of check-dams on sediment storage-release in Chabagou Watershed

Zhang Luan1,2 , Shi Changxing1※, Zhang Hao3 (1. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; 2. Graduate university of Chinese Academy of Sciences, Beijing 100049, China; 3. College of Information and Business, North University of China, Taiyuan 030051, China)

Abstract: For clarifying the response of sediment yield to the strengthening of human interventions in the middle Yellow River, Chabagou Watershed was selected as the study area to explore the relationship between development of check-dams and dynamic of sediment storage-release both in time and space. Construction of check-dams in the Chabagou Watershed started in the late 1950s, speeded up swiftly in the 1960s and 1970s, and nearly stopped in the 1980s and 1990s. The results showed that most of eroded sediment was stored in the Chabagou Watershed in the 1980s, with a sediment delivery ratio of 0.325. The low sediment delivery ratio can be attributed to the check-dams, which can not only trap sediment, but also reduce the frequency and intensity of hyper-concentrated flow to a greater extent. However, it is worth noting that the storage capacity of check-dams in the Chabagou Watershed had been decreased significantly due to filling up of early built dams as well as slowdown of dam construction since the 1980s. Moreover, the potentiality of sediment release from destroyed dams is increasing as a result of low design standards and poor maintenance of existing dams. Therefore, the role of check-dams as soil and water conservation measures should be paid adequate attention in the future. It is necessary to strengthen construction and management of check-dams for maintaining and even promoting their sediment trapping capacity. Key words: erosion, soil conservation, water conservation, sediment transport, sediment traps doi：10.3969/j.issn.1002-6819.2010.02.012 CLC number: TV5 Document code: A Article ID: 1002-6819(2010)-02-0064-06

Zhang Luan, Shi Changxing, Zhang Hao. Effects of check-dams on sediment storage-release in Chabagou Watershed[J]. Transactions of the CSAE, 2010, 26(2): 64－69. (in Chinese with English abstract)

 restructuring and rational water utilization, and improving 0 Introduction people's living and production conditions. The past 50 years Sediment problem is the key issue of the Yellow River. can be divided into four phases of check-dam construction, Though the opinion that the multi-year average sediment i.e. demonstration (1949-1957), widely promotion delivery ratio is close to 1 on the Loess Plateau has been the (1958-1970), accelerated construction (1971-1980) and basic understanding to the academic community for a long consolidation and reparation (after 1981). Now, a great time[1-2], soil erosion and sediment transport in the middle number of check-dams that retard sediment transport to Yellow River had become much more complicated due to downstream in Loess Plateau region in northern Shaanxi the strengthening of human interventions, and the regional Province have emerged. The dam system in the Chabagou variations in the response of sediment storage-release on Watershed is a typical example. It is recorded that soil and different space and temporal scales[3-5]. water conservation measures were implemented in the [6] In the long history of struggle against soil erosion, Chabagou Watershed first in the 1950s . By the end of people in Loess Plateau in China have created check-dam, 1989, both the quantity and quality of soil and water which is one of the most effective engineering measures in conservation project had been greatly increased. Many trapping sediment, resolving “hanging river” problem, studies have been done to elucidate the importance of [7-9] increasing basic farmlands of high quality, solving food check-dams in trapping sediment and reducing erosion . [10] problems, promoting returning farmland to forest, and Based on hydrological data, Xu and Sun indicated that improving eco-environment, as well as stimulating industrial sediment storage-release was affected strongly by sediment trapping and releasing of check-dams, which could act as Received date: 2009-05-07 Revised date: 2009-11-02 artificial sinks when they were empty and intact, and in Foundation item: National Natural Science Foundation of China（Grant No. contrast, as sediment sources when they collapsed or were 40971012） destroyed. However, the relationship between development Biography：Zhang Luan(1982－)，Ph D, Research direction: Soil erosion and of check-dams and dynamic of sediment storage-release conservation, Graduate School of the Chinese Academy of Sciences, Beijing both in time and space has not been explained in detail. 100049, China. Email：[email protected] Therefore, with more available detailed data of sediment ※Corresponding author：Shi Changxing(1963－), Ph D, Professor, Research direction: Fluvial geomorphology, Institute of Geographic Sciences and Natural load and check-dams in the Chabagou Watershed, and by Resources Research, Chinese Academy of Sciences, Beijing 100101, China. using statistical methods, Googleearth, Arcgis and other Email：[email protected] technology on raw data mining, authors intend to further 第 2 期 张 鸾等：岔巴沟流域淤地坝对泥沙存贮-释放的影响 65 investigate the relationships between temporal-spatial water conservation measures. In addition, sediment changes of sediment storage-release and the development reduction mechanism of check-dams was also explored by and construction of check-dams. analyzing ten-year average sediment delivery ratio in the watershed in the 1980s. For calculating sediment delivery 1 Study area ratio, authors used data of precipitation and sediment yield The Chabagou Watershed is located at the longitude of recorded at Caoping Station from 1980 to 1989[12], 109°47' and latitude of 37°31' and covers an area of 205 km2, Chabagou Digital Elevation Model (DEM) with a 25 m 24.1 km in length and 7.22 km in width on average. There resolution, 1︰250 000 Land-use data and 1︰1 000 000 soil are one main stream named Chabagou and 11 main branches properties database (from Data Center of Resources and in the watershed (Fig.1). The outlet station is set up at Environmental Sciences, Chinese Academy of Sciences). In 2 Caoping, with a drainage area of 187 km . order to quantify the effects of check-dams on sediment storage and release in the 1980s, the sediment delivery ratio was calculated. It is defined as the ratio of the suspended sediment load measured at the outlet to total soil erosion of a watershed: SDR=Y/T. In this study, the factor Y is the suspended sediment load measured at Caoping Station, and the factor T is calculated by RUSLE (Revised Universal Soil Loss Equation) equation with the channel erosion being taken into account. Details of the method for calculating soil erosion can be found in another paper of the same author (Zhang et al. [13], 2009). 3 Results and discussions 3.1 Development of check-dams 3.1.1 Construction time and number of check-dams Of 484 registered reservoirs and check-dams in the Chabagou Watershed, 83.68% is recorded with specific Fig.1 Schematic diagram of Chabagou Watershed construction time. The statistics of the amount and construction time of these dams give the following results: As a result of the continental dry climate, rainfall Construction of check-dams in the Chabagou Watershed distribution in the Chabagou Watershed is uneven, 70% began at 1953. Only 25 check-dams were built in the 1950s, concentrating in the three months from July to September mostly in 1958. In the 1960s, the number of check-dams and falling mainly in intensive and short rainstorms. With began to increase, and it reached 124 by the end of 1969. In broken terrain, destroyed natural vegetation and agricultural the 1970s, it was up to 248. In the 1980s and 1990s, there activities, the highly erodible loess in the Loess Plateau were only 13 newly built check-dams, and some existing tends to generate hyper-concentrated flows in rainstorms, check-dams were repaired or reinforced. Figure 2 gives the leading to serious soil erosion. The extensive occurrence of tendency of the development of check-dams in the hyper-concentrated flows on the Loess Plateau can be Chabagou Watershed. The trend of histogram graph also regarded as a zonal phenomenon[11].According to the reflects the development process of check-dams in the Loess observations at Zizhou Hydrological Station from 1954 to Plateau in northern Shaanxi region. 1958, the average and largest annual erosion modulus was 15 780 t/km2 and 23 670 t/km2, respectively. Located in the transitional zone with sandy loess and loess, the study area has been subjected to more intensive soil erosion as a result of silt-sized particle of the loess there besides other causes. To control the serious soil erosion, soil and water conservation measures, such as terraces, forests and grass, check-dams, have been put in practice on the Loess Plateau and developed to a large scale since the 1950s. 2 Data sources and methods The study of the relationship between the development and sediment-trapping effects of check-dams was based on data of reservoirs and check-dams in the Chabagou Fig.2 Changes in number of check-dams in 40 years Watershed, which was provided by local water authorities and include construction time, location, height, storage Before 1980, 372 dams were built. Among them 180 capacity and area, as well as the reserved area of soil and check-dams were more than 10 meters in height and more 66 农业工程学报 2010 年 than 6 670 m2 in area, and 63 of the 180 check-dams were number of dams in the 1960s was more than that in the more than 15 meters in height. The percentage of these two 1950s, but the dams concentrated in the central valley. In the categories of dams is shown in Fig.3. It can been seen that period of 1970-1979 much more dams were built and they the percentage of dams of more than 10 meters in height were widely distributed in the whole watershed and some showed a decreasing trend from the 1950s to the 1960s and appeared in the uppermost small gullies. an increasing trend after the 1960s, while that of the dams of more than 15 meters in height showed an increasing trend from the 1950s to the 1970s. The percentage of dams of more than 10 meters in height was lower than 50% in its highest and was much higher than that of dams of more than 15 meters in height, which was still lower than 37% in the 1970s. This indicated that, even being improved in the 1970s, most of the check-dams had a lower design standard in the Chabagou Watershed. This would greatly increase the risk of serious collapse of dams in future. Figure 4 shows the spatial distribution of dams in different periods. It can be clearly seen that the dams built in the 1950s were more concentrated, only in some branches of Fig.3 Changes in percentage of check-dams Liqugou, Yandonggou, Gaojiagou and Liujiagou. The with different scales

Fig.4 Location of check-dams in Chabagou Watershed in different periods

The above results showed that a lot of check-dams were collapsed. Results are as follows: constructed in the 1960s and 1970s. They had played a very In the booming period, sediment trapping of the dams important role in trapping sediment in the Chabagou was effective. However, the dams were filled gradually with Watershed which had only an area of 205 km2. However, the time. Up to 1978, 206 dams had been totally filled up, and fact is that heavy and concentrated rainstorms, although 143 dams were partly filled. In 1993, the number of partly short, usually cause a large volume of floods carrying a large filled dams decreased to 26. In 2001, only two of the 451 sediment load. These floods are mostly beyond the capacity check-dams had remaining capacity. Although some dams of small-scale check-dams, resulting in the damage and were heightened and repaired before the flood season in collapse of dams. According to Wang’s[14] (1996) report, in 2001, 106 dams were still totally filled-up (Fig.5). the rainstorms in August 1973 and 1975, 43.6% and 30.5% Some dams were heightened for several times every of dams were damaged in Yanchuan County and Yanchang three to five years for sustaining their capacity of silt County in Shaanxi Province, respectively. High-intensity detainment and promoting their capacity of flood prevention. rainstorms in rainfall data are common in Shaanxi Province. However, they were still threatened by extraordinary floods. For this reason, it is necessary to analyze the status of Statistics showed that there were 47 collapsed dams and 55 check-dams. totally destroyed dams within the whole watershed after the 3.1.2 The status of check-dams of different period flood season of 1978. The numbers increased to 204 and 70 Based on the records of reservoirs and check-dams in the before the flood season of 1993, and 223 and 120 in 2001, Chabagou Watershed in three periods, which include respectively. The collapsed and totally destroyed dams capacity, silted area, sediment volume, erosion amount and together account for 76.05% of the total (Fig.5). remaining capacity, as well as height, thickness and notes, Spatial distributions of collapsed dams, totally filled-up statistics of 451 check-dams is made by dividing the status dams and partly filled dams differ among the three periods of dams into four types: unfilled, filled, destroyed and mentioned above (Fig.6). Reasons for this phenomenon are 第 2 期 张 鸾等：岔巴沟流域淤地坝对泥沙存贮-释放的影响 67 quite complicated, and may result from the diversities of 3.2 Sediment reducing mechanism and benefit of repairing time, height, capacity, quality, etc. check-dams The role of check-dams in sediment trapping has been confirmed by many studies [8,15]. According to a survey of check-dams in Yulin and Yan’an carried out by Shaanxi Provincial Water Resources Bureau recently, there was total silted area of 43 286.7 hm2 behind 31 797 dams by the end of 1989. Report of Jiao[9] showed that the sediment trapping effects of single dams in the loess hilly-gully area in five watersheds, including the Huangfuchuan River, the Kuye River, the Jialu River and the Tuwei River, were 30.8%, 32.5%, 52.9%, 23.3% and 41.5%, respectively, indicating positive roles of dams in trapping sediment and reducing erosion. Our data support this finding, too. It could be Fig.5 Changes of status of check-dams in different periods calculated that the volume of silts behind dams in the Chabagou Watershed was 13 574 900 m3 and 16 590 600 m3 by the ends of 1978 and 1993, respectively. Assuming a bulk density of 1.35 t/m3, the mass of silts would be 18 326 100 tons and 22 397 300 tons, respectively. Therefore, in the 14 years from 1978 to 1993, about 4 071 200 tons of sediment was trapped by dams. It would be a total of about 2 908 000 tons in the 1980s if the yearly mean rate of sediment accumulation was the same. However, the mass of silts behind dams is much less than the difference between the calculated volume of soil erosion and sediment load measured at the outlet of the watershed. Our result showed that, the sediment delivery ratio in 1980s was 0.325, or the percentage of sediment storage was 67.5% in the watershed, while only 12.1% of eroded soil had been checked behind Fig.6 Status of check-dams in Chabagou Watershed in 2001 dams. This means sediment in Chabagou Watershed was unbalanced. It seems to be a mistake, but it is reasonable. It can be seen from the above analysis that dams in the Soil erosion in the Chabagou Watershed was serious in Chabagou Watershed have been developed greatly since the natural condition, even in the areas with bedrock exposed. 1950s. However, later in the 1970s, rainstorms destroyed The frequent hyper-concentration flows carried a great deal many dams and put many in danger. With fewer new dams of sediment out of the watershed. However, the being built in the 1980s and 1990s and the decrease of implementation of soil and water conservation measures in silting capacity of the poorly maintained dams, 92.8% dams the 1970s and 1980s, such as terraces, planting grass and in the Chabagou Watershed had collapsed, been destroyed or check-dams, changed this situation by altering local [6] filled-up before the rain season of 2001. Given by Ye , the micro-topography and increasing precipitation infiltration. preserved silting area behind dams built upstream of The decrease of runoff and sediment erosion was effective in Caoping Station from 1956 to 2000 validates the above facts reducing hyper-concentrated flow[16]. Xu[16] analyzed the (Fig.7). relationship between 5-year moving average value of hyper-concentrated flows and the area with soil and water conservation measures. His results suggested that the frequency of sediment-laden flows had been noticeably lowered due to the effects of soil and water conservation measures, especially check-dams, on erosion reduction. The comparison between sediment delivery ratio and the volume of silt behind dams in the Chabagou Watershed in the 1980s also showed that, in addition to sediment trapping, check-dams effectively reduced the frequency and intensity of hyper-concentration flows and sediment yield. Besides, check-dams also reduced erosion by raising erosion base level, which controlled the down-cutting of valleys and the Fig.7 Changes of silting area of check-dams extension of gully heads. from 1956 to 2000 68 农业工程学报 2010 年

spatial scales in hilly areas of the Loess Plateau[J]. North 4 Conclusions China, 2007, 27(9): 3572－3581. Check-dams in the Chabagou Watershed have played a [6] Ye Aizhong. Study on Simulation of Catchment Water Cycle very important role in reducing sediment yield by trapping in Changing Environment[D]. Wuhan: Wuhan Unversity, sediment and lowering the frequency and intensity of 2007. (in Chinese with English abstract) sediment-laden flows. However, this study also reveals some [7] Li Jing, Zheng Xinmin. Analysis on erosion reduction problems of check-dams in the Chabagou Watershed, such mechanism and sediment reduction function of as the lower design standards, lacking of large dams, poor check-dams[J]. Bulletin of Soil and Water Conservation, management. Conclusions and recommendations of this 1995, 15(2): 33－37. (in Chinese with English abstract) study are as follows: [8] Fang Xuemin, Wan Zhaohui, Kuang Shangfu. Mechanism 1) Constructing check-dams in the Chabagou Watershed and effect of silt-arrest dams for sediment reduction in the started in the late 1950s, boomed in the 1960s and 1970s, middle Yellow River basin[J]. Journal of Hydraulic and stagnated in the 1980s and 1990s. Most of the early built Engineering, 1998, (10): 49－53. (in Chinese with English dams had a low designing standard and a low capacity. In abstract) the booming period, sediment trapping of the dams was [9] Jiao Juying, Wang Wanzhong, Li Jing, et al. Silting land and effective. With the filling up of more and more dams in the sediment blocking benefit of check-dams in hilly and gully Chabagou Watershed, damage or collapse of dams in storms region on the Loess Plateau[J]. Transactions of the Chinese has increased with time. Society of Agricultural Engineering, 2003, 19(6): 302－306. 2) In addition to sediment trapping, check-dams (in Chinese with English abstract) depressed the sediment yield by reducing the frequency and [10] Xu Jiongxin, Sun Ji. Study of temporal variation of intensity of hyper-concentration flows and by reducing soil check-dam construction in the Wudinghe River basin and erosion in gullies through raising their erosion base level. some suggestions for some countermeasures[J]. Journal of 3) The role of check-dams as soil and water conservation Soil and Water Conservation, 2006, 20(2): 26 － 30. (in measures should be paid adequate attention in the future. It Chinese with English abstract) is necessary to strengthen construction and management of [11] Xu Jiongxin. Erosion caused by hyper-concentrated flow on check-dams for maintaining and even promoting their the Loess Plateau of China[J]. Catena, 1999, 36(1/2): 1－19. sediment trapping capacity and reducing the frequency of [12] Yellow River Conservancy Commission of Ministry of Water high sediment-laden flows. Resources of the PRC. Hydrology Yearbook of People's Republic of China— Hydrological Data of the Yellow River [References] Basin[Z]. Zhengzhou[s.n.]: 1980－1989. [1] Chen Yongzong. Time variation of origin of sediment of the [13] Zhang Luan, Shi Changxing, Du Jun, et al. Research on Yellow River and yield of sediment as a result of erosion[J]. sediment storage-release of a small watershed in loess Soil and Water Conservation in China, 1988, (1): 23－29. (in hilly-gully area[J]. Research of Soil and Water Conservation, Chinese with English abstract) 2009, 16(4): 39－44. (in Chinese with English abstract) [2] Yao Wenyi, Wang Weidong. Review of researches on the [14] Wang Wanzhong, Jiao Juying. Sedimentation caused by source of the Yellow River sediment[J]. Yellow River, 1997, rainfall erosion and runoff in Loess Plateau and sediment (6): 14－18. (in Chinese with English abstract) transport by Yellow River[M]. Beijing: Science Publishing [3] Xu Jiongxin, Yan Yunxia. Scale effects on specific sediment House, 1996. (in Chinese) yield in the Yellow River basin and geomorphological [15] Ran Dachuan, Luo Quanhua, Liu Bin, et al. Effect of explanations[J]. Journal of Hydrology, 2005, 307(1/2/3/4): soil-retaining dams on flood and sediment reduction in the 219－232. middle reaches of Yellow River[J]. Journal of Hydraulic [4] Fang Haiyan, Chen Hao, Cai Qiangguo. Effect of spatial Engineering, 2004, 5(2): 7－13. (in Chinese with English scale on suspended sediment concentration in flood season in abstract) hilly loess region on the Loess Plateau in China[J]. [16] Xu Jiongxin, Yao Wenyi, Han Peng, et al. Research on Environment Geology, 2007, 54(6): 1261－1269. Erosion Processes in the Middle Reaches of Yellow River by [5] Zheng Mingguo, Cai Qiangguo, Chen Hao. Effect of Coupling Climate-Landform-Vegetation[M]. Beijing: Science vegetation on runoff-sediment yield relationship at different Press, 2009: 170－173. (in Chinese) 第 2 期 张 鸾等：岔巴沟流域淤地坝对泥沙存贮-释放的影响 69

岔巴沟流域淤地坝对泥沙存贮-释放的影响

张 鸾 1,2，师长兴 1，张 灏 3 （1．中国科学院地理科学与资源研究所 陆地水循环及地表过程重点实验室，北京 100101； 2．中国科学院研究生院，北京 100049； 3．中北大学信息商务学院，太原 030051）

摘 要：为分析黄河中游流域产输沙对人类干预增强的响应机制，该文选取岔巴沟为坝系小流域研究区，探讨淤地坝的建设和发展 对流域内泥沙存贮-释放时空变化的影响。研究表明，20 世纪 80 年代岔巴沟处于泥沙存贮状态，10 a 平均泥沙输移比为 0.325，经 分析，始于 20 世纪 50 年代，并于 60、70 年代得到发展，80、90 年代趋于稳定的岔巴沟淤地坝拦截了大量泥沙是造成泥沙存贮的 主要原因。和拦沙作用相比，其减少高含沙水流发生频率，降低高含沙水流发育程度的作用更大。值得注意的是，淤地坝在几十年 的发展过程中可淤库容显著下降，多数原有坝地淤满，加上 20 世纪 80 年代以后坝体建设速度减缓，以及设计标准低，后期管理和 维护不利，垮坝和毁坝造成泥沙再释放的潜在性在增加。 因此，今后在对淤地坝作为一项重要的水保措施引起足够重视的同时， 维护和巩固现有淤地坝的拦泥库容也非常必要。 关键词：侵蚀，土壤保持，水资源保护，泥沙输移，淤地坝