Topographical surveying for improved assessment of sediment retention in check dams applied to a Mediterranean badlands restoration site (Central Spain)

Purpose

The effects of check dams used in restoration projects have been discussed in a number of papers in recent years. This paper studies the effectiveness of retaining sediments from check dams constructed in the badlands restoration site of Tórtoles, located in the Corneja River basin (Spain), using a new topographical method.

Materials and methods

In order to assess the sediment-retaining capacity of the check dams, we measured the volume of sediment trapped by 15 of the 123 check dams built in 1965. We carried out a detailed topographical survey using a Total Station, with an accuracy of ±1 cm, to measure cross sections of the sediment trapped by each check dam. The results were then compared with those of two simplified methods which consider the volume of retained sediment as a simple geometric figure.

Results and discussion

According to our results, 258 m³ of sediment has been retained by the check dams. These results show a significant discrepancy between the topographical method and the two other methods, whose values are consistently lower (14 to 20 %). According to our survey, the mean value for the volume of sediment retained by each check dam is 17.23 m³, versus 13.86 and 14.74 m³ when applying the other methods. Although there is a strong correlation between the volume of retained sediment computed by the topographical method and the other two methods (r ² from 0.96 to 0.94), the differences between them increase with the increasing size of the check dams. Therefore, total differences are expected to be more significant with larger check dams. The erosion rates, calculated on the basis of the retained sediment in the Tórtoles check dams, are 16–21 % lower when using the simpler methods. The bed slopes of the streams were reduced 12.44 % because of the presence of the check dams.

Conclusions

After having completed a more detailed topographical survey of the sediment trapped in the check dams, our results are more likely to estimate erosion rates and sediment yield correctly, thus leading to a better understanding of the effects of check dams on badlands restoration.     

A Biophysical and Economic Assessment of a Community‐based Rehabilitated Gully in the Ethiopian Highlands

Gully erosion reduces agricultural productivity by destroying valuable land resources, increases sediment concentrations, reduces water quality, and fills up reservoirs. Gully rehabilitation has proven to be challenging especially in the high‐rainfall areas of the Ethiopian Highlands and has therefore had limited success. This paper describes a successful low‐cost gully rehabilitation effort with community participation in the Birr watershed in the Blue Nile basin that begun in early 2013. Initially, farmers were reluctant to participate for religious reasons, but with the aid of local priests and respected elders, community discussions, and a visit to a rehabilitated gully, a consensus was reached to rehabilitate a 0·71‐ha upland gully. The rehabilitation measures consisted of regrading the gully head at a 45° slope, constructing low‐cost check dams from locally available materials, and planting Pennisetum purpureum grass and Sesbania sesban. At the end of the first post‐implementation rainy season, 2,200 tons of soil was conserved by the constructed check dams and newly planted vegetation, compared with soil losses of 680 and 560 tons in two untreated, nearby gullies. In 2014, an additional 3,100 tons of soil was conserved. In 2013, the marginal rate of return (MRR) on the gully rehabilitation investment was 2·6 based on the value of increased forage production alone. When we include trapped soil nutrient values, the rehabilitation MRR was increased to 10. Although these numbers are impressive, the best proof of the success was that farmers on their own initiative rehabilitated an additional five gullies in 2014. Copyright © 2015 John Wiley & Sons, Ltd.     

砒砂岩区典型淤地坝沉积泥沙特征及来源分析

黄土高原地区的淤地坝是拦减入黄泥沙的关键措施,尤以对泥沙具有绝对控制的"闷葫芦"淤地坝为甚。为研究淤地坝对侵蚀泥沙的拦蓄作用,以砒砂岩区皇甫川流域园子沟淤地坝为研究对象,采集坝地淤积剖面及沟间地、沟谷地表层样品,对沉积旋回进行断代分析,计算泥沙贡献率,反演其淤积过程。结果表明:坝地沉积泥沙粒径分布以2~0.05 mm砂粒为主,其次为粉粒、黏粒,砂粒中以极细砂和细砂占比最多。园子沟坝控流域内侵蚀性降雨事件对应的最小日降雨量为22.8 mm;淤地坝运行可划分为2个阶段,前期主要依靠坝体拦蓄泥沙,后期随着拦蓄泥沙的增多,减蚀作用凸显。坝地沉积泥沙主要来源为沟谷地,贡献率达71.4%,沟间地为28.6%,其中沟间地侵蚀产沙并非受植被唯一影响,在降雨量>45.4 mm时,地形因素会限制侵蚀的加剧。     

基于MIKE模型的不同淤地坝型组合情景对小流域侵蚀动力和输沙量的影响

为科学认识黄土高原淤地坝建设对小流域侵蚀动力过程的影响,通过分布式水文模型MIKE SHE和一维水动力模型MIKE 11耦合模拟了王茂沟流域的洪水过程,并计算了流域主沟不同断面的侵蚀动力参数和不同坝型组合的减沙效益。结果表明:(1)淤地坝建设在不同程度上改变了小流域沟道的侵蚀动力分布,坝系建成后沟道的侵蚀动力参数减幅最大。(2)小流域径流侵蚀功率表现为上中游剧烈变化,下游趋于稳定,且下游径流侵蚀功率明显小于上游。(3)淤地坝建设可以有效减小流域的输沙量,其中单独建设骨干、中型、小型坝相比流域未建坝时,输沙模数分别减少24.74%,47.11%,64.11%;流域坝系建成后减沙效益最明显,流域输沙量减少83.92%。研究成果可为黄土高原淤地坝减沙效益评估提供科学参考。     

Sediment Yield Deduction from Check–dams Deposition in the Weathered Sandstone Watershed on the North Loess Plateau,China

As the basic unit of erosion and sediment yield, it was critical to determine the amount of soil erosion and sediment yield in the small watersheds for sustaining a reasonable water resource and sediment regulation system. In this study, we determined the sediment yield from the dams‐controlled watershed on the North Loess Plateau. Three check dams in the watershed were investigated by drilling ten‐hole sedimentation cores. The corresponding flood couplets were dated according to thickness of deposition layers, distribution of sediment particle size and historical erosive rainfall events. On the basis of the check dams capacity curve, the soil bulk density and the thickness of couplets, the deposit mass of check dams, and then the sediment yield of watershed at different temporal and spatial scale were deducted. In total of the 33, 60 and 55 couplets were corresponded to individual flood events in the dam MH1# from 1976 to 1984, the dam MH2# from 1985 to 2007, and the dam MH4# from 1981 to 2009, respectively. The specific sediment yield for flood events was 1,188.5–11,527.9 Mg km⁻², 1,278.6–17,136.7 Mg km⁻², and 3,395.9–33,698.5 Mg km⁻², and the annual average sediment yield was 10,728.6 Mg (km² · a)⁻¹, 12,662.9 Mg (km² · a)⁻¹, and 16,753.3 Mg (km² · a)⁻¹ in dam MH1#, MH2# and MH4# controlled watershed, respectively. The sediment yields were inversely proportional to the dams – controlled areas. For the whole watershed, the annual average sediment yield was 14,011.1 Mg (km² · a)⁻¹ from 1976 to 2009. There were large amounts of sediments (42.3–50.5%) were intercepted gradually along the way from small watersheds to the river channel. And the minimum rainfall for sediment deposited in the dams was greater than 20 mm in this watershed. The results of this study suggested that the sediments retained behind check dams were helpful to quantifying the amount of erosion sediment yield and understanding the soil erosion evolution in the small and ungauged watersheds. Copyright © 2016 John Wiley & Sons, Ltd.     

黄河流域鄂尔多斯十大孔兑淤地坝减沙效应

为了定量评价十大孔兑地区淤地坝的减沙效益,基于历史资料整理与实地详查,统计了十大孔兑地区1986年以来现存淤地坝的数量和分布特征;采用淤积体概化法,确定了影响淤地坝减沙量的主要参数,并计算了研究区354座淤地坝的减沙量。结果表明：十大孔兑354座淤地坝累计减沙3.205 61×10⁷t,其中减沙量最大的孔兑为西柳沟,达1.239 76×10⁷t;通过分析不同时段淤地坝的减沙特征表明,1986—1999年、2000—2009年和2010—2018年3个时段的淤地坝减沙量分别为4.946 6×10⁶t, 1.155 57×10⁷t, 1.555 38×10⁷t。十大孔兑地区淤地坝具有显著的减沙作用,具有很高的减沙指标(达5 720.33～58 141.81 t/座),2000年以后的两个时间段内,随着坡面林草措施的增加,淤地坝减沙量增加,表明在这一地区,淤地坝仍然是最有效的水土保持措施之一。     

Run-off and sediment yield in relation to differential gully-plugging schemes in micro-catchments of Shiwaliks in the lower Himalayas

Gully-management strategies adopted in the Shiwalik range of hills in the lower Himalayas of India, which involve treatment of only higher order gullies, have not been successful. A study was conducted in the four selected micro-catchments in the region to monitor run-off and sediment yield variations in relation to differential gully-plugging schemes. One of the study catchments (catchment III) with highest run-off and sediment yield was selected for an alternative scheme of gully management. In this, all the first-order and 25–30% of the second-order gullies were plugged with locally available stones, and native grass vegetation wasplanted on the upstream side. Other catchments (catchments I, II and IV) were treated as per the the conventional method of gully plugging involving the installation of loose stone check dams in the highest order gullies. The highest run-off coefficient (15.5%) for the period 2000–2006 was registered in catchment III. However, this decreased to 12.8% during 2007, when the catchment was treated using an alternative gully-management scheme. The sediment yield from catchment III decreased by 20% in 2007 from 15.2 t ha^?1 during 2000–2006. The results indicate that to control gully erosion, lower order gullies should be treated as a priority.     

Using LiDAR data to map gullies and headwater streams under forest canopy: South Carolina,USA

The southeastern Piedmont of the USA was severely gullied during the early 20th century. A thick canopy established by reforestation in many areas now inhibits the identification or mapping of gullies by aerial photography or other conventional remote sensing methods. An Airborne Laser-Scanning (ALS or LiDAR) mapping mission flown for the U.S. Forest Service in April, 2004 acquired bare-Earth topographic data. This paper tests the ability of the ALS topographic data to identify headwater channels and gullies for two branching gully systems in forested areas and to extract gully morphologic information. Comparisons are made with field traverses using differential GPS and reference cross sections measured by leveling surveys. At the gully network scale, LiDAR data provide accurate maps – the best available – with robust detection of small gullies except where they are narrow or parallel and closely spaced. Errors in mapping channel location and network topological connectivity under forest canopy increase with attempts to identify smaller features such as large rills. The ability of LiDAR data to map gullies and channels in a forested landscape should improve channel-network maps and topological models. At the gully reach scale, attempts to use LiDAR data to extract gully cross-section morphologic information under forest canopy were less successful due to systematic underestimation of gully depths and overestimation of gully top widths. Limited morphologic accuracy of the data set at this scale may be due to low bare-Earth point densities, shadowing of gully bottoms, and filtering of topographic discontinuities during post-processing. The ALS data used in this study are not suitable for detailed morphometric analysis or subtle change detection to monitor gullies or develop sediment budgets. Data collection may be improved by orienting flights over gullies and with increased point densities through improved scanner technology or better filtering and software capabilities to differentiate between vegetation and ground surfaces.     

Effectiveness and geomorphological impacts of check dams for soil erosion control in a semiarid Mediterranean catchment: El Cárcavo (Murcia, Spain)

The construction of transverse structures (check dams) is a widely used method in Spanish Mediterranean areas to stabilise gullies and ephemeral streams, to reduce channel incision and to prevent sediment deposition downstream. The effectiveness of check dams and their effects on the morphology of ephemeral channels (ramblas) were investigated in a semiarid, highly degraded catchment. In the study area, 36 dams were surveyed, of which 29 were filled up with sediments, 2 had been destroyed and only 5 had still not completely filled with sediments. The streams above the dams held sediments, which resulted in a decrease in the longitudinal gradient. Field observations of changes in the cross-sectional shape of the stream channel, the composition of channel bed material, and bankfull stage measurements indicated that the dams cause erosion downstream. The amount of sediments stored by the dams was found to be higher than the amount of eroded material in the downstream reaches of the dam.     

Check dams and sediment control: final results of a case study in the upper Corneja River (Central Spain)

Journal of Soils and Sediments - The sediment yield and erosion rate in an area can be estimated by calculating the volume of sediment retained by check dams. However, results can show unrealistic...     

Morphological Similarity of Channels: From Linear Erosional Features (Rill,Gully) to Alpine Rivers

The geometric characteristics of incised features such as channels, rills, ephemeral gully, gully, represent the erosional transport regime and the fluvial dynamic equilibrium, and thus it is critical for the understanding of the long‐term evolution of natural, agricultural, and anthropogenic landscapes. This paper examines the morphological similarity of channelized erosion in two different environments such as Alpine landscapes and cultivated hillslopes. The first dataset comprises six rivers in the Italian Alps, three in the Carnia region and three in the Dolomites, where erosion is mainly the effect of discharges with high sediment loads or landslides and debris flows. The agricultural areas dataset includes rills, ephemeral gullies, and gullies surveyed in literature. This research highlights that the eroded volume in Alpine rivers is in line with that of agricultural landscapes or badlands around the world. Dolomites rivers of colluvial origin, flowing on soils that are not particularly deep and subject to natural disaggregation, tend to behave similarly to ephemeral gullies. Contrarily, channels that exhibit evident alluvial morphologies and coarse grain sizes are more similar to gully erosion. At different spatial scales, the results demonstrated that length–volume equations calibrated on rills, ephemeral gullies, gullies and badlands, might be feasible also for Alpine channels. The research areas present soils and bedrock lithology that differs from those in literature, thus suggesting that the morphology of linear erosion is independent of the intrinsic soil characteristics. Differences emerged between Dolomites and Carnia rivers: this highlights the importance of taking into account in future analyses other forcing factors (e.g. climate) on land degradation processes. Copyright © 2017 John Wiley & Sons, Ltd.     

无定河淤地坝拦沙措施时间变化的分析与对策

运用大量实测资料对无定河淤地坝及其拦沙效应进行了研究。坝地面积增加率在20世纪70年代达到峰值。80年代发生显著衰减，90年代进一步衰减。用水文法对无定河流域水土保持措施的减沙效益进行了估算．结果表明，减沙效益从70年代开始急剧增大，并在70年代末、80年代初达到峰值，随后有减小的趋势。历年新增坝地面积从60年代中期开始急剧增大，并在70年代初达到峰值．随后有减小的趋势。由于后续淤地坝的建设未能及时跟上，新增坝地面积在70年代末和80年代中大幅度减少后．随着原有的淤地坝逐渐淤满失效，淤地坝减沙效益衰减。在这一因素的影响下，无定河产沙量在70年代开始大幅度减小，但在1986～1996年，修建于60年代末、70年代和80年代初的淤地坝相继淤满失效之后．后续淤地坝建设未能跟上，故无定河产沙量有增加的趋势。基于本研究，我们建议．在无定河的水土保持中应加强淤地坝建设，实现淤地坝的持续拦沙效应，才能使入黄泥沙减少的趋势能够长期持续下去。     

Natural and anthropogenic controls on soil erosion in the Internal Betic Cordillera (southeast Spain)

Soil erosion in southeast Spain is a complex process due to strong interactions between biophysical and human components. Significant progress has been achieved in the understanding of soil hydrological behavior, despite the fact that most investigations were focused on the experimental plot scale. Although experimental plots allow exploring the effect of multiple biophysical and anthropogenic factors, they provide limited insights in the combined effect of all factors acting together at the landscape scale. In this study, area-specific sediment yields (SSY) have been estimated based on the volume of sediment trapped behind 36 check dams in the southeast of Spain. Low SSY-values were reported (mean = 1.40 t ha⁻¹ year⁻¹: median = 0.61 t ha⁻¹ year⁻¹). SSY variability could be explained for 67% by catchment characteristics such as drainage area, soil characteristics, land cover, average catchment slope, and annual rainfall. The low SSY values are probably caused by the agricultural abandonment that occurred over the past decades and allowed the recovery of natural vegetation. Furthermore, our results suggest that the soils have eroded in the past to such an extent that nowadays not much sediment is detached by overland flow due to residual enrichment of clay and stones. Also, sediment is to a large extent trapped locally in the catchment, as indicated by the negative relationship between SSY and catchment area.     

黄土高原梯田和淤地坝坡沟治理措施对产流产沙的协同效应

黄土高原地区的梯田和淤地坝措施发挥了重要的水土保持功能,然而现有的研究主要关注单个措施的减水减沙效应,对坡沟治理措施综合配置协同调控水沙过程的作用一直认识不清。因此,该研究为解析梯田和淤地坝措施对水沙过程的协同调控效应,构建了10个坡沟系统物理模型,设置了对照组（CO）,单一措施组（梯田措施（T0）,4种因淤地坝淤积导致坡沟区域的坡长缩短（L1、L2、L3和L4））和组合措施组（梯田与4种因淤地坝淤积导致坡沟区域的坡长缩短的综合配置（T1、T2、T3和T4））,进行降雨强度为90 mm/h的室内模拟降雨试验,量化不同试验方案下坡沟系统的产流产沙过程。结果表明：1）梯田措施和淤地坝淤积导致坡沟区域坡长缩短均有效调控了坡沟系统的产流产沙过程,梯田能分别减少46.30%～83.59%的径流总量和25.82%～82.41%的泥沙总量,淤地坝导致坡沟区域坡长缩短能分别减少7.87%～33.42%的径流总量和10.20%～30.57%的泥沙总量。2）不同试验方案下坡沟系统的产沙率和产流率之间满足线性关系,而累计产沙量和累计产流量满足幂函数关系。3）综合措施配置发挥了“1+1> 2”的水土保持...     

Slope and rainfall effects on the volume of sediment yield by gully erosion in the Souar lithologic formation (Tunisia)

The Souar lithologic formation in semi-arid Tunisia is undergoing severe gully erosion which is threatening soil and water resources. Soil conservation strategies have focused more on terracing than on gully control techniques, since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown. The paper reports investigations into the sediment yield provided by head-cut as well as sidewall–floor erosion of first order gullies on gentle and steep slope catchments underlined by the Souar lithologic formation. We measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments, respectively. Two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established. The treatment with a Geographic Information System (Arc View) of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls–floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights. Total gully erosion was on average 1.66 m³ ha^− 1 year^− 1 for the gentle slopes and 5.603 m³ ha^− 1 year^− 1 for the steep slopes. Sidewalls–floor contribution in total erosion was on average 81.5% for the gentle slopes and 77.8% for the steep slopes. We found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds. Two equations between these two variables were established both for gentle and steep slope catchments.     

水土保持措施对无定河流域沟道-河道系统泥沙收支平衡的影响

流域系统可以分为坡面系统和沟道-河道系统2大单元,可以分别建立泥沙收支平衡关系。结果表明：1）实施水土保持措施以后,无定河流域系统泥沙收支平衡中各变量均随时间而变化。沟道-河道系统泥沙输移比发生了极显著的减小趋势,泥沙存储量发生了显著的增大趋势,流域产沙量的变化发生了较显著的减小趋势,坡面净侵蚀量有所减少,但变化趋势不显著。2）对于不同的泥沙收支平衡变量的变化而言,水土保持措施变化和降雨变化的贡献率是不同的;对坡面净侵蚀量的变化而言,汛期降雨的变化起着决定性的作用,贡献率高达90.82%,坡面水土保持措施的贡献率仅为9.18%;对沟道河道系统泥沙存储量的变化而言,淤地坝拦沙的变化起着决定性的作用,贡献率高达76.16%,汛期降雨变化的贡献率仅为23.81%;对流域产沙量的变化而言,汛期降雨和水土保持措施的变化都起着重要作用,前者贡献率为57.84%,后者贡献率为42.16%。3）对沟道-河道系统泥沙输移比RSDRc的变化而言,淤地坝拦沙的变化起着决定性的作用,贡献率高达87.27%,汛期降雨变化的贡献率仅为12.73%。     

Evaluation of the Effectiveness of Forest Restoration and Check‐Dams to Reduce Catchment Sediment Yield

Reforestations and check‐dams are two commonly used measures to reduce soil erosion rates and sediment export from highly eroding catchments. Here, we evaluated the impact of the construction of 94 check‐dams and land use changes (caused by agricultural abandonment and reforestations) on sediment yield in the Upper Taibilla catchment (320 km², SE Spain) from 1956 to 2000. We combined land use change analysis, field surveys, and application of the WaTEM‐SEDEM erosion and sediment yield prediction model for nine scenarios combining land use maps (1956, 1987, and 2000) and different numbers of check‐dams throughout the catchment. Land use changes alone reduced sediment yield up to 14%, but in combination with check‐dams, the reduction in sediment yield reached 44 ± 6%. Sediment yield reduction was higher in smaller sub‐catchments, with, on average, a higher transport capacity than larger catchments, illustrating the scale dependency of human impacts on sediment fluxes and the buffer capacity of larger catchments. From an economical perspective, the construction of check‐dams was estimated to be more expensive than reforestation programs in the studied catchment, while adding more check‐dams did not always result in a proportional reduction of sediment yield. This indicates that optimizing check‐dam distribution relative to land use patterns is crucial to decrease catchment sediment yield. Check‐dams have a large and instantaneous impact on sediment yield over a restricted time period, while reforestations have important sustained effects at a lower economic cost. These contrasting effects require a careful evaluation for optimal effective catchment management. Copyright © 2014 John Wiley & Sons, Ltd.     

Sediment management options for the lower Ebro River and its delta

Background, Aim and Scope  Past and present management of the Ebro catchment have altered water, sediment and nutrient fluxes of the lower Ebro River and its delta. The construction of the Mequinensa and Riba-Roja dams during the 1960s disrupted the sediment transport continuity. As a result, the lower Ebro River and its delta are facing a reduction in sediment delivery which is estimated to be up to 99% of its original yield (about 3 × 10⁷ t/yr). Consequently, about 45% of the emerged delta will be under the mean sea level by 2100 due to subsidence and sea level rise, whereas the delta coast is retreating at a rate of several meters per year in the mouth area. This paper aims to establish the basis for a sediment management plan directed to offset the effects of the sediment delivery deficit of the Ebro delta. Main Features  A new management plan named ‘Integrated Plan for the Protection of the Ebro Delta’ (PIPDE) is being presently elaborated in order to develop sustainable management of the Ebro River and delta through an integrated management of water, sediment and habitats, in order to achieve European Union (EU) Water Framework Directive (WFD) requirements. Among other aspects, the plan aims to restore the sediment flux of the lower Ebro River by means of both the removal of the sediment trapped behind the dams and the transport of the sediment downstream of the reservoirs to the river mouth and delta plain. Results  Preliminary studies show that the ‘flushing flood’ method has lower costs and is the most adapted method to transfer the sediments retained into the Riba-Roja dam. The required sediment load to stop coastal retreat in the mouth area and to compensate relative sea level rise represents 10 times the present suspended load (0.021 g/l), but is 10 times lower than the total volume of sediment delivered to the sea under natural conditions. Sediment delivery to the delta plain can be accomplished through the rice irrigation system, a method used prior to dam construction. Discussion  Problems of achieving a sustainable management of water and sediment are mostly linked to reservoir management. Technical problems associated with by-passing sediments through the reservoirs can be solved through operational and structural changes. Benefits of sediment flow recovery are multiple, including maintenance of the reservoir capacity, possible decline of invasive species, reduction of elevation loss and coastal retreat in the delta. Conclusions  The partial restoration of sediment fluxes in the lower Ebro River and its delta is technically feasible and environmentally desirable, but further detailed studies need to be carried out before the plan can be implemented. Perspectives  Overall, the sustainability of the lower Ebro River and delta can only be guaranteed by the implementation of a new reservoir management concept where the ecological and morphological values, as well as the economical and social values, have to be taken into consideration.     

坝地沉积旋回泥沙养分变化及其对小流域泥沙来源的解释

黄土高原广泛分布的坝地沉积泥沙中赋存了大量小流域侵蚀特征及侵蚀环境变化的信息,泥沙特性的变化则是这些信息的直接体现。该文通过对比分析淤地坝沉积旋回泥沙中和坝控小流域内不同泥沙源地土壤中有机质、全氮、全磷和全钾的含量,发现小流域内土壤养分含量变异性明显大于沉积旋回泥沙中的变异性,沉积旋回泥沙养分含量与沟壁土壤中的相接近,其中与沟壁中的全氮、全磷和全钾无显著差异(p>0.05),但显著小于荒草地和坡耕地中的有机质、全氮和全磷含量(p<0.05),表明淤地坝运行期间小流域泥沙主要来源于沟壁坍塌和沟道扩展,重力侵蚀和沟蚀是主要侵蚀类型;有机质和全氮在坝地沉积旋回中呈明显阶段性变化,分析认为其反映了农村土地联产承包责任制对小流域土地利用和土壤侵蚀的影响。     

黄河中上游地区水利水保措施蓄水拦沙作用分析评价

对黄河中上游地区水利水保措施的蓄水拦沙作用分析的结果表明,现阶段水保措施年均蓄水量为10亿m~3,年均拦沙量3亿t,支流水库和淤地坝的拦沙量占水保措施拦沙量的77.8％。这种蓄水拦沙作用是在80、90年代降雨量减少的情况下得出的,由于前期积累、隐蔽、潜伏着许多泥沙问题,某些支流遇到较大暴雨产沙量激增,这对黄河下游可能会造成一定影响。当前应当把更多的精力和投资放在沟道的整治和利用上,大力修建控制性的大型骨干水库或淤地坝。