关键词: 生态排水沟, 泥沙, 农业面源污染, 坡度, 流量

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