Abstract:

With the ongoing intensification of agriculture, non-point source pollution has emerged as a leading cause of global water quality degradation. This is particularly pronounced in regions with concentrated sloping farmland, where rainfall-induced runoff carries significant loads of sediment into adjacent rivers and lakes. This process not only elevates water turbidity but also introduces nutrients such as nitrogen and phosphorus, subsequently triggering eutrophication and posing a substantial threat to regional aquatic ecological security and the sustainability of agricultural development. As a nature-based solution, ecological drainage ditches systems mitigate this issue by incorporating vegetation or porous media to increase hydraulic roughness. This effectively reduces flow velocity, prolongs hydraulic retention time, diminishes sediment transport capacity, and thereby enhances the sedimentation and retention of pollutants. To systematically evaluate the sediment retention efficiency of different ecological drainage ditches structures and their responses under varying hydraulic conditions, this study conducted field scouring experiments on four ditch types—three ecological ditches (ED1, ED2, ED3) and a traditional concrete control (CD)—at the Jingouxing Soil and Water Conservation Demonstration Park in Ganzhou City. The configurations were as follows: ED1 is a concrete pier-porous brick ditch, featuring vegetated shale porous bricks on the sidewalls, a concrete-hardened bottom, and staggered concrete piers; ED2 is a fully-lined vegetated porous brick ditch, where both the sidewalls and bottom are constructed with porous bricks and entirely covered with grass; ED3 is a composite substrate ditch, with sidewalls lined with Zoysia japonica turf and a permeable base consisting of layered gravel, fine sand, and red soil. In ED1 and ED2, the porous bricks were vegetated with a mixture of local grass species, including Zoysia japonica, Paspalum wettsteinii, and Cynodon dactylon, at a density of 200-300 plants·m⁻² following a 105-day establishment period. The control ditch (CD) was a typical smooth, three-side-hardened concrete channel without vegetation. The experimental setup involved 6-meter-long straight segments for each ditch type, tested at slopes of 1° (gentle) and 9° (steep) with three replicates per configuration. Each segment was equipped with an inlet, and monitoring cross-sections were established at 2 m, 4 m, and 6 m downstream. Scouring experiments were performed using water with a sediment concentration of 10 g·L⁻¹ at flow rates of 70 L·min⁻¹ and 140 L·min⁻¹. During each run, the flow arrival time, velocity, and depth were meticulously recorded at each cross-section. After the flow stabilized, water samples were collected simultaneously from all three sections at 30-second intervals. These samples were left to settle, the supernatant was decanted, and the remaining sediment was dried and weighed to determine sediment concentration, enabling a comprehensive analysis of longitudinal sediment variation and the trapping efficiency of each ditch type under different slope and flow regimes. The key findings are as follows: 1) The sediment reduction efficiency of all ecological drainage ditches significantly surpassed that of the traditional concrete ditch, with an overall performance ranking of ED2 (8.51%-18.01%)>ED3 (8.17%-13.22%)>ED1 (3.62%-7.11%)>CD (2.3%-4.59%). 2) Increasing the slope generally reduced trapping efficiency; for instance, ED1 decreased from 7.11% to 3.62%, and ED2 from 18.01% to 9.33%, whereas ED3 demonstrated greater resilience, maintaining a relatively high efficiency between 9.13% and 13.22%. Similarly, higher flow rates typically led to decreased performance, with the efficiencies of ED1, ED2, and ED3 dropping to 4.95%, 8.51%, and 8.17% respectively under the high-flow condition. 3) Structural design fundamentally determined hydraulic resistance; ED2 achieved the highest efficiency under low-flow conditions but was highly sensitive to hydraulic changes, while ED3’s multi-layer infiltration and buffering mechanisms conferred optimal stability across varying slopes and flows. 4) Operational and maintenance requirements differ: ED1 necessitates focused sediment removal from the wake zones behind its concrete piers; ED2 requires regular cleaning of its porous brick voids and root systems to prevent clogging, alongside vegetation management; and ED3 needs periodic monitoring and clearing of accumulated sediments within its bottom media layer to sustain permeability. 5) For future applications, designs should be tailored to regional topography and hydraulic conditions, incorporating dynamic monitoring of sediment gradation along the ditch and periodic scouring tests to balance high interception efficiency with long-term operational stability. This study systematically elucidates the regulatory mechanisms of different ecological drainage ditches structures on sediment transport, providing a robust theoretical foundation and practical technical support for structural optimization, operational maintenance, and the effective control of agricultural non-point source pollution.

Key words: ecological drainage ditch, sediment, agricultural non-point source pollution, slope, flow rate

摘要：

坡耕地受降雨冲刷易引发水土流失，导致泥沙及携带的营养盐进入下游水体，威胁区域生态环境安全。为探究不同生态排水沟结构对泥沙削减效率的影响及其在不同水力条件下的响应特征，在赣州市金钩形水土保持示范园建设了3种生态排水沟（ED1，混凝土墩-多孔砖排水沟；ED2，植被多孔砖排水沟；ED3，砾石－细砂－红壤复合基底排水沟）和1条传统混凝土沟（CD）。通过开展含沙质量浓度10 g·L⁻¹、坡度1°、9°与流量70、140 L·min⁻¹的野外冲刷试验，分析了不同坡度与流量组合条件下的沿程泥沙浓度变化与削减效率。结果表明：1）沟型结构对泥沙削减效率影响显著，整体表现为ED2（8.51%－18.01%）>ED3（8.17%－13.22%）>ED1（3.62%－7.11%）>CD（2.31%－4.59%）；2）坡度增加导致排水沟削减效率下降，ED1由7.11%降至3.62%，ED2由18.01%降至9.33%，而ED3仍保持在9.13%－13.22%；3）流量增加也引起削减效率普遍降低，在高流量条件下，ED1、ED2和ED3的削减效率分别降至4.95%、8.51%、8.17%；4）ED2在低流量下泥沙削减效率最高（18.01%），但对水力条件变化敏感，而ED3由于其多层渗透和缓冲机制，在不同流量和坡度条件下均表现出最佳的稳定性。研究结果可为生态排水沟型优化设计以及控制农业面源污染提供科学依据。

关键词: 生态排水沟, 泥沙, 农业面源污染, 坡度, 流量