The invention discloses a step type low elevation greenbelt for purifying surface
rainfall runoff. The step type low elevation greenbelt comprises a road shoulder, a high position region and a low position region from inside to outside, wherein the elevation of the road shoulder, the elevation of the high position and the elevation of the low position region are sequentially and gradually decreased. The road shoulder, the high position region and the low position region are connected through a herbal
plant belt. The high position region sequentially comprises a planting soil layer I, a coarse sand layer and a gravel layer I, herbal plants are planted on the planting soil layer I, a pipeline is laid in the gravel layer I, and the other end of the pipeline is led to the low position region. The low position region sequentially comprises a planting soil layer II, a fine sand layer, an
oxygen slow-release material layer, a gravel layer II and a
geosynthetic clay liner, and an overflow opening is formed in the low position region. Herbal plants are planted on the planting soil layer II, and a perforated drainage
pipe is laid in the gravel layer II. Water is converged to the overflow opening through the drainage
pipe, and the overflow opening is communicated with a rainwater
pipe duct. According to the low elevation greenbelt, SS entering the low elevation greenbelt is remarkably reduced, the content of dissolved
oxygen in a low elevation greenbelt matrix is increased through an
oxygen slow-release material, and the degradation capacity of COD and
nitrogen and
phosphorus pollutants is enhanced.