Hydrological Cost – Benefit Analysis of Stormwater Management Strategy in Northern Coastal Mountain Parks

Objective Mountain parks serve as a crucial green open space within the city. Due to their complex and variable hydrogeological conditions, they often exhibit hydrological characteristics like high flow rate, poor infiltration performance and short confluence time, making them susceptible to soil erosion and related disasters such as flash floods and downstream waterlogging. Unlike southern mountainous cities with plentiful rainfall and numerous water systems where rainwater management focuses on rapid drainage and flood prevention, northern coastal mountainous cities experience less rainfall. This research aims to address the rainwater issues in the northern coastal mountainous area, and proposes a stormwater management strategy that combines cost-effective hydrological methods with rainwater storage and utilization.

Methods Initially, the current site conditions are assessed, and ArcGIS is used to simulate changes in elevation gradient, surface property, and soil infiltration in the Daiwang Mountain area in Yantai City. This helps analyze the site’s hydrological process characteristics. Based on the upper planning requirements and the hydrological conditions of the Daiwang Mountain area, this research introduces a mountainous hydrological regulation strategy called “source reduction, process interception, and terminal storage and utilization”. A rainwater management system oriented towards “infiltration, detention, and storage and utilization” is established to facilitate layered storage from top to bottom, thus enhancing rainwater storage and utilization. With annual runoff control rate being kept qualified and the volume of detention, regulation and storage facilities kept equal, three different stormwater management and control schemes with different focuses are compared: Scheme S1 focuses on source reduction and interception, Scheme S2 focuses on terminal detention and utilization, and Scheme S3 integrates upstream mountains and downstream residential areas for multi-level control. Finally, the SWMM software is used to analyze and evaluate the hydrological cost − benefit performance of these strategies under various precipitation scenarios.

Result The proposed hydrological regulation strategy for the mountainous area is to transform the upstream source area, which produces the largest volume of runoff, and adopts horizontal steps and fish scale pits to intercept surface runoff and enhance soil moisture, thus improving the environment for vegetation restoration and water conservation. In the midstream area, runoff is collected from scattered upstream slopes, and facilities like ecological side ditches and flood intercepting ditches are established alongside roads and contours to manage rainwater runoff for transmission and purification. This helps achieve interception, infiltration, and peak-shifting regulation and storage. In the downstream area prone to waterlogging, biological detention facilities and wet ponds are adopted for centralized storage. A rainwater regulation and storage tank is also employed for storing and utilizing rainwater for irrigation purposes. The hydrological cost − benefit performance of the three strategies are simulated and evaluated. The simulation results indicate that increasing vegetation at the source can significantly improve the total runoff reduction rate, and using facilities at the end can greatly enhance peak flow reduction. The regulation performance notably declines under high-intensity rainfall due to spatial and rainfall limitations. The utilization of runoff differs in different seasons, mostly concentrated in summer with high rainfall, while storage pools remain idle in other seasons. The hydrological cost − benefit performance is influenced by control efficiency and construction and maintenance costs, with Scheme S3 showing the best cost − benefit ratio under the same rainfall conditions.

Conclusion The research constructs a hydrological cost − benefit analysis framework for mountain parks and explores a suitable stormwater management strategy that balances economic and practical considerations, aiming to mitigate the issues of alternating droughts and floods and the scarcity of rainwater resources. It is expected to provide some reference for the planning and construction of mountain parks in northern coastal mountainous areas and other areas with similar natural conditions.