Low impact development (LID) is a storm management philosophy. This paper aims at choosing the LID for urban storm management by comparing the efficiency in the south urban district in the Taiyuan Basin. Firstly, we set up a 1D–2D model to simulate the hydrological and hydraulic process of the area. Then the efficiency of different LID scenarios was analyzed by ratio of surcharging pipeline, percentage of ponding road, external outflow, infiltration, surface runoff, facility storage, and LID area ratio. It was found that the continuous porous pavement and rain garden are beneficial for use in residential and commercial settings in urban areas, and the rain garden performs more effectively and efficiently than the continuous porous pavement. The area occupied by LID might be under 20% of the impervious building area, because the LID performance was not improved significantly with the LID area when the ratio exceeded 20%. The LIDs could be more useful for small return periods and short duration storms, and could not replace conventional runoff management practices and drainage systems.

Varying active stream network lengths (ASNL) is a common phenomenon, especially in hilly headwater catchment. However, direct observations of ASNL are difficult to perform in mountainous catchments. Regarding the correlation between active stream networks and stream recession flow characteristics, we developed a new method to estimate the ASNL, under different wetness conditions, of a catchment by using streamflow recession analysis as defined by Brutsaert and Nieber in 1977. In our study basin, the Sagehen Creek catchment, we found that aquifer depth is related to a dimensionless parameter defined by Brutsaert in 1994 to represent the characteristic slope magnitude for a catchment. The results show that the estimated ASNL ranges between 9.8 and 43.9 km which is consistent with direct observations of dynamic stream length, ranging from 12.4 to 32.5 km in this catchment. We also found that the variation of catchment parameters between different recession events determines the upper boundary characteristic of recession flow plot on a log–log scale.

As a storm management philosophy, low impact development (LID) is used to control the surface flow and its pollution, especially in the intending urban area in China. Finding the proper LID plan to balance the cost and surface flow effect is very important for the administrators of the cities. Firstly, we combined the SWMM with NSGA II to find the Pareto set of these optimal LID plans. Then, a structural decision-making approach was used to select the proper scheme from the Pareto set. The numerical tests consisted of 40 combinations of different return periods and durations and were conducted. The result shows that the SWMM-NSGA II model is a distributed model which could be used to find the multi-objective optimization LID plans for an intending urban area. When the SDA is used to select the suitable scheme from the Pareto set composed by the optimal alternatives, the weights could reflect the management demand of people. The LIDs might be more effective for more frequent, lighter, and shorter duration storms. It could cost too much, but the control effective might not be obvious in a heavy storm.

The flood of the urban in a basin might be more serious than the urban district in the plain. In this paper, we take the south urban district in the Taiyuan Basin as a case, and set up a 1D-2D model to analyse the runoff and drainage during different designed storm scenarios. The hydrological model calibrated by the designed storm and flood is taken as an inflow boundary of the plain, instead of observed data series. The 1D-2D model is used to model the drainage, surface flow, and flooding. The model shows that the flooding might occur in the urban district during the three designed 24-hour rainfalls, 20 years, 50 years and 100 years, and the roads between building blocks and the low-lying farmland might experience heavy flooding.

Accurate estimation of loss of life caused by dam breaches is critical for reservoir risk management and emergency planning. Traditional methods rely on static population data with poor timeliness and low spatial resolution. This study proposes a real-time estimation method by integrating population heat maps with land use data. A temporal variable is introduced to distinguish newly inundated populations from those already counted in previous time steps, thereby avoiding double counting during flood routing, while differences in public understanding of flood severity are considered to evaluate loss of life under various warning conditions. Taking the Shiyan Reservoir in Shenzhen as a case study, the BREACH model and HEC-RAS 2D are employed to simulate dam breach and flood routing. Results show that the final inundation area reaches 16.99 km², with residential areas accounting for 97.13%. The total at-risk population after land use correction is 200,963, which is 32.7% higher than the uncorrected estimate of 151,482. Loss of life estimates are highly sensitive to warning time and public understanding, reaching 129,691 under the most adverse conditions (no warning, vague understanding) but dropping to 20 when warning time exceeds 1 h with precise understanding. The proposed method provides an effective tool for real-time urban dam breach risk assessment.