Gully Land Consolidation Research Articles

Assessing the effects of soil and water conservation in gully land consolidation using the modified SWAT-Terrace model

To alleviate the competition for cropland between ecological restoration and agricultural production, a Gully Land Consolidation (GLC) project has been widely executed in the Chinese Loess Plateau. This project involves mechanically excavating slopes and filling gullies to expand cropland area. Therefore, in the context of climatic and topographical changes, an assessment of the impact of GLC as a key land use measure of water and sediment in space and time is urgently needed. However, due to scale effects, there is a lack of relevant assessments for the GLC. This study utilized the Soil and Water Assessment Tool (SWAT) and SWAT-Terrace model to analyze the temporal-spatial changes of water and sediment in the Yanhe watershed during 1985–1998 (R1) and 1999–2017 (R2). Additionally, it assessed the effectiveness of GLC in erosion control across different sub-basin clusters. The results showed that (1) at the temporal scale, the runoff and sediment decreased by 30.09 % and 72.73 % respectively, during R2 compared to R1; (2) at the spatial scale, 56 % and 71 % of the sub-basins located in the central and northern parts of the watershed showed a reduction in water and sediment yield, respectively, during R2 compared to R1, while the remaining sub-basins located in the southern part showed an increasing trend in water and sediment yield; and (3) the GLC can reduce 1.17 %-1.93 % of water yield and 0.94 %-1.91 % of sediment yield in the three clusters of sub-basins. The assessment of the soil and water conservation effects of the GLC is beneficial to policymakers in designing effective land management plans and the extension of the project to other regions.

Responses of Soil Moisture to Gully Land Consolidation in Asian Areas with Monsoon Climate

Groundwater resources are essential for sustaining ecosystems and human activities, especially under the pressures of climate change. This study employed Electrical Resistivity Tomography (ERT) to assess the impact of Gully Land Consolidation (GLC) engineering on the groundwater hydrological field of small watersheds in the China Loess Plateau (CLP). Results revealed ample subsurface water storage in backfilled areas, primarily migrating along the original river path owing to topographical limitations. Although the distribution patterns of soil moisture in each backfilling block varied slightly, the boundaries of soil moisture content and variation mainly appeared at depths of 8 m and 20 m underground. Significant moisture variation occurred across the 0–20 m underground layers, suggesting the 8–20 m layer could function as a groundwater collection zone in the study area. Human activities could disturb groundwater, altering migration pathways from the original river path. An optimized “Drainage–Conveyance–Barrier” system is proposed to enhance GLC sustainability, involving upstream groundwater level control, midstream soil moisture management, and downstream hydrological connectivity improvement. These findings carry substantial implications for guiding the planning and execution of GLC engineering initiatives. The novelty of this study lies in its application of ERT to provide a detailed spatial and temporal understanding of soil moisture dynamics in the GLC areas. Future research should focus on factors such as soil types and topographical changes for a comprehensive assessment of GLC’s impact on small watershed groundwater hydrology.

TIC-driven sustainable land use mode in the Loess Plateau: A case study of gully land consolidation project in Yan'an City, China

The Loess Plateau is one of the most severely eroded areas in the world. The complexity of the multiple challenges facing the Loess Plateau entails the support of scientific and systematic innovations in land use. Based on technological innovation cluster (TIC) theory, this paper develops a self-circulation structure model for the TIC to analyze the hierarchical structure of the land-use innovations in the Loess Plateau. Then, employing the self-circulation structure model and taking the “Gully Land Consolidation Project” (GLCP) as a case study, this paper proposes one TIC-driven sustainable land use mode (TSLUM). A TIC has been developed among innovations in the TSLUM. The structure of TSLUM consists of three types of innovations: basic, related, and infrastructure innovations. Basic innovations are generally radical innovations that breed related, and infrastructure innovations. Diffusion-based and reversal-based mechanisms govern the evolution of the TSLUM. These two clustering mechanisms integrate with each other and jointly promote the development of the TSLUM in a self-circulation way. Furthermore, the TSLUM exhibits multiple functions, such as optimizing gully-slope interaction mechanism, providing continuous driving forces, consolidating the achievements of the “Grain for Green Project”, bolstering rural livelihoods, and fostering some feasible ways for food security. The results obtained will be useful for advancing sustainable land use and regional sustainable development in the Loess Plateau via TICs effectively and systematically.

Intensive land restoration projects alter mechanisms underpinning spatiotemporal soil moisture variability at a catchment scale: A case study in China

Soil moisture (SM) is a critical factor for material circulation and energy exchange in Earth’s critical zone, but it is spatially and temporally variable. This study aimed to provide new insight into spatiotemporal SM variability and its associative controls in areas where land restoration projects have been implemented. Specifically, we compared environmental controls on spatiotemporal SM variability in deep soil layers (0–500 cm) of two paired catchments, one of which was treated by the Gully Land Consolidation (GLC) project and the other which was not, where the slopes of both catchments had initially been impacted by the Grain for Green (GFG) program. For this purpose, we used the empirical orthogonal function (EOF) to decompose spatial and temporal SM anomalies. Two dominant spatial and temporal EOF anomalies (EOF1 and EOF2) were obtained from six soil layers in both catchments, with an explained variance of 86%–97% and 32%–53%, respectively. These spatial anomalies that derived from spatial structures exhibited similar characteristics and controls in both catchments, while underlying temporal SM dynamic mechanisms differed. Temporal dynamics of the treated catchment were lower in the gully area (a relative flat region), while the opposite was true for the gully area (at a lower elevation) in the untreated catchment. The GLC and GFG programs both altered catchment scale temporal SM dynamic forcings. Results obtained from this study are helpful for understanding spatiotemporal SM variability with associated the hydrological processes in areas where the intensive land restoration projects have been implemented at a catchment scale.

Effects of gully land consolidation on soil organic carbon, soil enzymes and its influences on maize yield

The change characteristics of 5 indicators of soil organic carbon (SOC) content, dehydrogenase activity, protease activity, catalase activity, and maize yield were analyzed at 0a before and 3, 4, and 8 years after remediation in the study area. Results showed that the coefficient of variation (CV) of each index in the study area was generally small, the variation degree of soil organic carbon content was the highest, and the variation degree of catalase activity and maize yield was the least. After the implementation of the gully land consolidation, the CV of each index in the gully showed a decreasing trend, and the distribution of each index in the gully tended to be uniform. With the increase of remediation years, SOC content, soil enzyme activity and maize first yield showed a trend of decrease and then increase, and the change trend of each index was slightly different at gully head, the middle of gully and the gully outlet, the change is significant. At the gully head, the SOC content did not return to the level of 0a after 8a of remediation, and the other indicators returned to the level of 0a or higher than that of 0a. At the gully head, at p < 0.05 level, maize yield showed a very significant positive correlation with catalase activity, and a negative correlation with protease activity. In the middle of gully, there was a significant positive correlation with organic carbon content, soil protease and catalase activities, and it was negatively correlated with dehydrogenase activity but not significantly. At the gully outlet, there was a very significant positive correlation with protease activity. Bangladesh J. Bot. 52(2): 459-466, 2023 (June) (Special)

Effects of gully land consolidation on soil organic carbon, soil enzymes and its influences on maize yield

The change characteristics of 5 indicators of soil organic carbon (SOC) content, dehydrogenase activity, protease activity, catalase activity, and maize yield were analyzed at 0a before and 3, 4, and 8 years after remediation in the study area. Results showed that the coefficient of variation (CV) of each index in the study area was generally small, the variation degree of soil organic carbon content was the highest, and the variation degree of catalase activity and maize yield was the least. After the implementation of the gully land consolidation, the CV of each index in the gully showed a decreasing trend, and the distribution of each index in the gully tended to be uniform. With the increase of remediation years, SOC content, soil enzyme activity and maize first yield showed a trend of decrease and then increase, and the change trend of each index was slightly different at gully head, the middle of gully and the gully outlet, the change is significant. At the gully head, the SOC content did not return to the level of 0a after 8a of remediation, and the other indicators returned to the level of 0a or higher than that of 0a. At the gully head, at p < 0.05 level, maize yield showed a very significant positive correlation with catalase activity, and a negative correlation with protease activity. In the middle of gully, there was a significant positive correlation with organic carbon content, soil protease and catalase activities, and it was negatively correlated with dehydrogenase activity but not significantly. At the gully outlet, there was a very significant positive correlation with protease activity. Bangladesh J. Bot. 52(2): 459-466, 2023 (June) (Special)

Retracted: Effects of Different Soil Modifiers on Salt Improvement and Distribution, Crop Growth of the Gully Land Consolidation on Loess Plateau

Retracted: Effects of Different Soil Modifiers on Salt Improvement and Distribution, Crop Growth of the Gully Land Consolidation on Loess Plateau

Model experimental study on the failure mechanisms of a loess-bedrock fill slope induced by rainfall

Large-scale gully land consolidation projects have been implemented on the Loess Plateau of western China. These projects have formed a large number of fill slopes, which are prone to failure induced by rainfall. However, the failure mechanisms of the loess-bedrock fill slope, especially the influence of the weak interlayer between the loess fill and bedrock on slope failure, are not clear. In this study, a laboratory flume model experiment was carried out to investigate rainfall infiltration processes and failure mechanisms of a loess-bedrock fill slope induced by rainfall. The volumetric water content, pore water pressure, wetting front migration, and deformation characteristics of the slope were analyzed to reveal the effects of the weak interlayer on slope failure. The results show that rainfall-induced failure of loess-bedrock fill slope exhibited characteristics of mode transformation, initiated by the local failure of the slope toe and gradually transforming into a multi-stage rotational slide-earthflow and gully erosion with continued rainfall. The maximum migration rate of the wetting front in the weak interlayer is about 3 times that in loess fill, occurring in the weak interlayer within a depth of 0.64 m (about 16 m in the prototype). The preferential flow formed in the weak interlayer accelerated the saturation of the fill slope and generated seepage force towards the outside of the slope, which makes the upper fill slope more prone to shear failure along the weak interlayer. These results provide a theoretical basis for preventing or mitigating related risks associated with gully land consolidation projects on the Loess Plateau.

Effects of the Gully Land Consolidation Project on Geohazards on a Typical Watershed on the Loess Plateau of China

From 2011 to 2013, a mega project, known as the Gully Land Consolidation Project (GLCP), was implemented in the hilly gully region atop China’s Loess Plateau. However, the GLCP involved large-scale slope excavation and gully backfilling that changed the local geological environment, which led to serious geohazards, such as erosion, soil salinization, and dam failure. In this study, various geohazards caused by the GLCP in the Gutun watershed (GTW) were investigated by combined remote sensing analysis, geophysical exploration, and field surveys, and the relationships between the hazards were also explored. According to the achieved results, increased soil erosion with an average doubling from 2018 to 2020 is widely distributed in the GTW. Furthermore, 195 areas containing clear evidence of salt precipitates were observed in some of the newly created arable lands, especially downstream of the dam. This was mainly attributed to the high water table, evaporation, and soluble salt concentration of the loess. Fifty-nine newly built silt dams, primarily located in the branch channels and at the gully mouth of the Gutun channel, broke in 2020. The osmotic damage and softening caused by the combined effect of the incomplete compaction of the dam body and concentrated heavy rainfall were the main reasons of the dam breaks. The different types of disasters in the GTW after the implementation of the GLCP show a strong spatial relationship that follows the surface water flow path and forms a disaster chain consisting of slope erosion, silt dam breaks, and the soil salinization of near-dam farmlands downstream. This disaster chain amplifies disaster risks and losses. These findings can guide the improvement of the GLCP and inform geohazard mitigation strategies in areas impacted by the GLCP.

Effects of the Gully Land Consolidation Project on soil erosion and sediment yield on the Loess Plateau, China

AbstractLand consolidation can increase the area of arable land and improve the ecology and environment and is widely used worldwide. The Gully Land Consolidation (GLC), as a special type of land consolidation, significantly impacts soil erosion. The purpose of this study was to investigate the effect of the GLC on soil erosion and sediment yield under different rainfall events and hydrological years in the Xingshuyaozi watershed on the Chinese Loess Plateau, where the GLC area accounted for 10.36% of the watershed. A computer model integrated with the Chinese soil loss equation (CSLE) and the continuity equation of sediment was used. Sediment connectivity before and after the GLC was compared to illustrate the effect of the GLC on sediment yield. The results showed that the reduction in soil loss increased with increasing rainfall amount, and the reduction rate of soil erosion was over 50%. The GLC had the greatest effect on soil erosion in wet years. The GLC effectively decreased sediment at the outlet of the watershed, with over 99% of the sediment being trapped. The reduction efficiency of soil erosion and sediment yield decreased in order of wet year, normal year and dry year. The decreased soil erosion and sediment yield resulted from the significantly lowered slope gradients and sediment connectivity after the GLC. These results indicate that the GLC is an effective soil and water conservation measure. These results can provide technical support for the application of the GLC and policymaking.

Agronomic technology to promote sustainable utilization of newly created farmland in the Chinese Loess Plateau

AbstractThe new farmland created by land consolidation often faces the problems of poor soil structure and low productivity, which cause potential degradation risk. The Gully Land Consolidation Program (GLCP) significantly increased the quantity of farmland in the Chinese Loess Plateau (LP), but the research on a comprehensive method of simultaneously improving soil quality, agricultural profit, and utilization efficiency of newly created farmland (NCF) is relatively scant. This study explored an agronomic technology to improve soil quality, agricultural profit, and utilization efficiency NCF by the GLCP in the LP. Our field experiment was carried out in Yangjuangou catchment with seven soil treatments and planting Brassica napus (B. napus) on these soils: dry mixing Malan Loess and red clay at volumetric ratios of 1:0 (MR10), 5:1 (MR51), 2:1 (MR21), 1:1 (MR11), 1:2 (MR12), 1:5 (MR15), and 0:1 (MR01). The results showed that: the soil microstructure, physico‐chemical properties, and productivity of NCF were significantly improved after soil reconstruction by dry mixing Malan Loess and red clay. More specifically, the MR51 boosted the root thickness and fresh weight of B. napus by 78.69% and 45.01% compared to that of red clay (MR01). Crop optimization by the B. napus helped to increase the agricultural profits of NCF. The proposed three portfolios of B. napus' silage, vegetable plus rapeseed, and vegetable plus silage enhanced the profits by 35.39%, 57.05%, and 66.93% in comparison with that of traditional crop planting, respectively. Therefore, industrial integration through effective, ecological and economic (3E) agriculture could advance sustainable utilization of NCF. Further, developing efficient agriculture, animal husbandry, agricultural products processing industry, and ecological tourism would enhance the multi‐functional value of farmland. Our study suggests that targeted agronomic technology based on agricultural geographical engineering oriented to human‐environment interaction can provide technical support for minimizing the degradation risk of NCF and generating more sustainable development in ecologically fragile areas.

Impacts of ecological programs on land use and ecosystem services since the 1980s: A case‐study of a typical catchment on the Loess Plateau, China

AbstractChina' Loess Plateau, which was once dominated by sloping fields with poor farming conditions and serious soil erosion, has experienced a series of ecological programs. This article sought to explore the impacts of ecological programs on land use and ecosystem services in a typical catchment of China's Loess Plateau from 1984 to 2017, and thus understand what needs to be improved for future ecological programs. The findings showed that: (a) Due to the implementation of various ecological programs, the land use structure was optimized, and vegetation coverage was significantly increased, especially with the implement of the Grain for Green (GFG) Program. (b) The change of the total ecosystem service value (ESV) presented a U‐shaped curve. The total ESV decreased under the Comprehensive Management of Small Catchments Program, and increased significantly since the implementation of the GFG. The rapid increase stage can be traced to the effects of the Gully Land Consolidation Program, reflecting the time lag effect of ecological programs on the improvement of ecosystem services. (c) The various ecosystem services were improved significantly, except for the food provisioning value (FPV). The abandonment of croplands without consolidation determined the decline of the FPV, implying the necessity for a land‐use efficiency boost. Our research proposed to build up an actor network to integrate local governments, rural cadres, villagers, enterprises, and natural resources, especially land resources, into ecological programs to ensure ecological restoration and activate the factors of production, thus securing the sustainable development of China' Loess Plateau.

Effects of Different Soil Modifiers on Salt Improvement and Distribution, Crop Growth of the Gully Land Consolidation on Loess Plateau

Due to the strong evaporation and leakage loss, secondary saline-alkali was the main problem in the watershed of gully land consolidation on Loess Plateau. Through field farming experiments, five modifiers (maize stalk (MS), humus acid (HA), Yan Ke (YK), He Kang (HK), and nanobiochar (NB)) were studied to investigate the effects of these soil modifiers on soil water and salt distribution, leaf photosynthetic characteristics, and maize growth and yields, as well as economic benefits in secondary saline-alkali soils of gully land consolidation watershed on Loess Plateau in 2019 and 2020. The results showed that soil modifiers could increase the water-holding capacity of the soil, reduce the salt content of the soil profiles, and decompose the accumulation of salt. The maximum desalination rate obtained in 2019 and 2020 increased, respectively, by 71.57% and 46.02%, compared to that in the control treatment. Soil modifiers could increase the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and decreased the intercellular CO2 concentration (Ci). The output increased by 13.63%-31.84%, and revenue increased by 6.48%-38.01%. According to analyzing the production of soil modifier application, we found that the highest net profit was achieved when HK application rate was 52.4 kg/ha. Therefore, this study suggested that 52.4 kg/ha might be recommended as an appropriate soil modifier application strategy to deal with crop growth and improve economic benefit in secondary saline-alkali soils of Northwest China.

Effects of the Gully Land Consolidation Project on Runoff and Peak Flow Rate on the Loess Plateau, China

The Gully Land Consolidation (GLC) project, aiming to create land for agriculture on the Loess Plateau, heavily interfered with the underlying surface and thus affected the hydrological process. The purpose of this study was to investigate the effects of the GLC on the surface runoff and peak flow rates of watershed on the Loess Plateau under different rainfall events and hydrological years. A GIS-based Soil Conservation Service Curve Number (SCS-CN) model was used. The results showed that GLC reduced the mean event surface runoff by 6.2–24.7%, and the reducing efficiency was the highest under light rain events. GLC also decreased annual surface runoff, and the reducing efficiency was 12.04% (normal year) > 7.63% (wet year) > 4.45% (dry year). In addition, GLC decreased the peak flow rate of the watershed by 8.1–30.2% and prolonged the time to peak flow rate. The efficiency of GLC in reducing the peak flow rate was higher under light rain events than that under extraordinary storm events. The reason for the decrease in runoff and peak flow rate after GLC was that the GLC decreased the slope gradient and hydrological connectivity of the watershed. The results will provide guidance for the application of GLC on the Loess Plateau and watershed management for similar regions.

Evaluation of the impact of the Gully Land Consolidation Project on runoff under extreme rainfall

AbstractExtreme rainfall is an important driver of soil erosion and land damage. The Gully Land Consolidation program (GLCP) was first launched in 2011 as a major land reclamation practice to increase farmland in the Loess Plateau of China. Studying the impact of artificial projects on hydrology can help humans to respond to the various water issues, but the assessment of the effects of the GLCP on extreme rainfall‐induced water runoff at watershed scale is currently lacking. Our study used the soil and water assessment tool (SWAT) to evaluate the influence of the GLCP at different locations and areas on water runoff under extreme rainfall events in the Yanhe watershed. Results showed that: (1) the GLCP can improve the interception of surface runoff, with interception efficiency in downstream of the watershed approximately twice that at midstream and entire watershed as well as seven‐times that at the upstream; (2) when GLCP measures are evenly distributed in a watershed, as the area of GLCP increases from 76.40 km2 (1% of watershed area) to 382.01 km2 (5%), the interception of surface runoff increases by 0.77 mm; (3) and the GLCP can increase soil infiltration and groundwater recharge. This research is expected to provide insights into the optimized layout of the GLCP at watershed scale. Correspondingly, policymakers can refer to this information in developing policies on the sustainable use of land.

Spatiotemporal soil water storage variation comparison between newly formed and untreated gully land sites under a land restoration project and associated implications on land management

Soil water storage (SWS) can effectively be used as an important indicator to manage soil water resources in water-limited ecosystems, being strongly linked to land-use and land management changes. The Government of China launched the Gully Land Consolidation (GLC) project in 2011 to reclaim landforms and resolve land scarcity and food shortages in the Chinese Loess Plateau (CLP) without endangering the environment. Corollary effects of this project were alterations to original landscapes and associated hydrological processes. However, temporal dynamics in available soil water of the newly formed land for cultivation purposes remain unclear. Accordingly, this study measured SWS to a 5 m soil depth over a 5-year period at two gully sites, one newly formed under the GLC project (i.e., the experimental site) and the other left untreated (i.e., the control). SWS exhibited similarly weak temporal variation at both gully sites (coefficient of variation [CV] = 6% at the experimental site; CV = 11% at the control site). Although SWS always negatively correlated to mean temperature and wind speed (p < 0.05) with no observable hysteresis, SWS responded to precipitation at both sites with obvious hysteresis (experimental site = two month hysteresis; control site = three months hysteresis). Seasonal SWS characteristics confirmed the lag response to precipitation. Moreover, spatial SWS patterns differed distinctly at both sites. The mean proportion of available SWS to the available water holding capacity was 69% at the experimental site, indicating that stored soil water was available for crop cultivation without the threat of water shortages. Our results provide new insight into spatial and temporal SWS variation in newly formed land engineered by restoration projects. Furthermore, clarifying SWS temporal dynamics and spatial distributions based on long-term monitoring is essential to evaluate, model, and manage water resources in areas affected by anthropic activities.

Characteristics and prevention mechanisms of artificial slope instability in the Chinese Loess Plateau

Numerous artificial slopes emerged in the watersheds of the Chinese Loess Plateau (LP) after the Gully Land Consolidation project (GLCP) that cut slopes to create farmland in the gully, which had incurred instabilities over time and could potentially resulted in soil erosion and geological hazard. This paper explored the characteristics and prevention mechanisms of artificial slope instability after the GLCP with field investigation in a typical watershed and the Back Propagation Neural Network (BPNN) method. The results showed that: (1) 439 instabilities induced by infiltration and erosion were found in 79 artificial slopes. (2) The difference of soil moisture and failure mode resulted in the instability degree of shady slope and lower slope were significantly higher than that of sunny slope and upper slope. (3) Among the surface condition factors, slope instability volume was significantly influenced by gradient, soil compactness, height and soil shear strength. Platform instability volume had great connection with soil compactness and its shear strength. (4) A “Drain-Improve-Green-Reinforce (DIGR)” system was proposed as the prevention mechanism for artificial slope instability, which included drainage system, soil improvement, vegetation protection, and reinforcement engineering. Taken together, this research provides the scientific reference for a better understanding and prevention of artificial slope instability, which would contribute to ensuring GLCP effectiveness and ecological security in the LP.

Measuring the Ecological Safety Effects of Land Use Transitions Promoted by Land Consolidation Projects: The Case of Yan’an City on the Loess Plateau of China

Land consolidation projects play an important role in promoting agricultural land use transitions, ensuring national food security, and accelerating the construction of ecological civilization. The Loess Plateau in China is a typical ecologically fragile area, where the Gully Land Consolidation Project (GLCP) has been implemented recently and had a major impact on local ecological safety. In this study, we established a quantitative evaluation model for ecological safety effects from the four aspects of dam safety, slope stability, efficient farmland, and effective management, and then scientifically measured the ecological safety effects of land use transitions promoted by land consolidation projects. Three small watersheds (Gutun, Yangjuangou and Luoping) within the GLCP area were employed to verify the evaluation model for ecological safety effects. The results showed that the GLCP can effectively improve the ecological environment and promote the development of modern agriculture, but the ecological safety of gullies and slopes in some areas may also facing a series of threats due to improper project management measures. Among them, Gutun had the highest ecological safety evaluation value, followed by Yangjuangou, while Luoping had the lowest value. The indicator system and evaluation method established in this research could be helpful to systematically diagnose the problems and scientifically guide the implementation of the GLCP from the perspective of ecological safety.

Effects of land-use management on soil erosion: A case study in a typical watershed of the hilly and gully region on the Loess Plateau of China

The effect of land use on erosion over space and time is relevant. In this study, two types of land-use management practices, the gully land consolidation (GLC) project and the land consolidation (LC) project, were applied on the Loess Plateau. Based on the soil erosion that occurred from 2010 to 2019, the spatial distribution, spatiotemporal evolution and susceptibility map of soil erosion were analyzed by geospatial analysis, statistical methods and frequency ratio (FR) models. The results showed that the implementation of the GLC project can have two effects on soil erosion. Firstly, a large amount of slope erosion was caused by slope excavation in the GLC watershed; secondly, the amount and scale of gully erosion were effectively controlled by hydraulic engineering. In addition, the unreasonable hydraulic engineering of the LC project can cause large areas of soil erosion. The influencing factors of gully erosion can be ranked as follows: reservoir > elevation > dam land > flow length > geology > LS. Three aspects of engineering optimization measures for the GLC project were proposed: 1. Slope excavation should be reduced, and diverse slope protections should be implemented in this project, especially for the bottom of the slope, which should adopt different measures than the top of the slope. 2. For trenches within 1.2 km of the gully head, more attention should focus on soil and water conservation measures than on land leveling. 3. Hydraulic engineering and irrigation and drainage engineering should effectively cooperate with leveling projects and adjust the applied measures to the local conditions and the natural shape of the original rivers. As a new land-use management approach, our results highlight that little is known about the effect of the GLC project on soil erosion, and our results can provide specific guidance for the next step of project implementation.

Evaluating the flow and sediment effects of gully land consolidation on the Loess Plateau, China

Gully land consolidation (GLC) is a slope-gully reclamation program that was implemented after “Grain for Green” project on the Loess Plateau, China. Through the GLC project, the Chinese government planned to increase the area of cropland by 337.80 km2 from 2013 to 2017. To quantify the impact of GLC on runoff and sediment transport, the coupled SWAT (Soil and Water Assessment Tool) model, which was integrated with a process-based terrace algorithm, was employed in this research. The results showed that the improved SWAT model was proven to be a powerful tool for detecting the effect of GLC on flow and sediment discharge. The effect of GLC on flow and sediment loading was concentrated in the flooding period, its runoff interception efficiency was 169,350 m3/(km2·yr), and sediment trap efficiency was 3979 t/(km2·yr), showing that it had good flow and sediment reduction benefits. However, the GLC project drastically altered the water and sediment flux equilibrium, and excessive expansion was likely to lose parts of riparian-ecosystem functions of the downstream river. In view of this, we integrated the improved SWAT (embedded in the terrace module), double-mass curve and Pettitt test to identify the recommended ratio of GLC area to the total area in the Yanhe watershed. The results demonstrated that if the reclaimed gully area accounted for 0.8% (61 km2) of the total area (7608 km2), the runoff abruptly changed. Therefore, the reclaimed gully area should remain within 0.8% of the total area in the Yanhe watershed, if so, GLC not only alleviates the contradiction between agricultural development and ecological restoration, but also gives full play to its functions of reducing flood and restricting sediment transport.