Subcatchment division and simulation precision of rainwater pipe network model

In recent years,it is common for cities to accumulate rain and flood during rainstorm.On the one hand,due to the negative impact of human activities on the environment,extreme rainstorm events occur frequently.On the other hand,with the acceleration of urbanization,urban hardening road surface increases,green space decreases,urban rainwater infiltration capacity is insufficient,easy to form waterlogging water.To solve urban waterlogging problem,urban waterlogging model needs to be built.An important part of urban waterlogging model is urban stormwater pipe network model.The key step of urban rainwater pipe network model construction is the division of subcatchment area,and the division result has great influence on the simulation accuracy of urban rainwater pipe network. Based on the theory of surface hydrological analysis of urban DEM,a basin analysis based Thiessen polygon subcatchment division method was proposed to solve the problem of inaccurate division of urban subcatchment area.This method took into account the effect of topography on the simulation accuracy of stormwater pipe network model.Basin analysis was carried out based on the raster data of the high resolution urban digital elevation model,and the runoff unit with concentrated catchment area was divided.The elevation variation in the runoff unit was small,and the runoff unit was defined as the primary sub-catchment area.The primary catchment area was revised to ensure that there are pipe network nodes in each primary catchment area.The primary catchment area was subdivided by Thiessen polygon method and the corresponding sub-catchment area was obtained. Taking a certain area in Beijing as an example,the basin analysis based Thiessen polygon subcatchment division method was compared with the two most commonly used subcatchment partitioning methods:manual drawing method and traditional Thiessen polygon method.The manual drawing method is a method for professionals to manually delineate the sub-catchment area corresponding to each pipe network node according to DEM elevation raster data,satellite image and data of different land use types in the study area,and then refine ground object elevation data.The classification process of this method is tedious and the workload is heavy,but it can accurately match the catchment area served by the actual pipe network nodes.Thiessen polygon method uses geographic information system software to delimit molecular catchment area based on inspection well,which is quick,simple and easy to operate.Based on the simulation results of downhole liquid level peak,peak emergence time,flow peak,peak emergence time and total runoff,the simulation accuracy of different catchment division methods was analyzed and the advantages of basin analysis based Thiessen polygon subcatchment division method were evaluated.The case study showed that the error between basin analysis based Thiessen polygon subcatchment division method and measured data was the smallest,and the deviation of the peak value of underground liquid level,peak flow value and total water amount were 1.115%,1.301% and 6.796%,respectively. The indexes of the model obtained by the Thiessen polygon method to divide the molecular catchment area had great deviations from the measured values,among which the total water amount deviation is 40.343%,showing a poor fitting degree.Moreover,the model flow peak value of Thiessen polygon method was significantly smaller than that of manual drawing method,resulting in low accuracy of simulation results.The deviation between the manual drawing method results and the measured data was small,which met the requirements of the specification and had high precision.The basin analysis based Thiessen polygon subcatchment division method had a small deviation between the simulated results of molecular catchment and the measured values,which met the specification requirements.Compared with the manual drawing method,the index error was smaller and the model accuracy was higher.Therefore,the urban stormwater network model constructed by the method proposed to divide the molecular catchment area had high precision,and the method proposed was simpler to operate than manual drawing method,which can reduce the workload and improve the drawing efficiency.

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