Sponge City Infrastructure and Stormwater Management Planning for Zhenjiang, China

The Challenge

In Zhenjiang, the lack of adequate stormwater conveyance and management in urban areas has been identified as the primary reason for increases in flooding and degraded water quality. Rapid urbanization and commercial development in China have led to major flooding events, causing damage to infrastructure and the environment, and, in some locations, has led to human fatalities. Considering these issues, stormwater management has become an important focus for the Chinese government.

In April 2015, the government announced the first 16 pilot cities for the “Sponge Cities” initiative. These pilot Sponge Cities, including Zhenjiang, are conceptually envisioned to be adaptive, comprehensive, and environmentally friendly, where urban developments act as systems that can absorb, store, infiltrate, and treat stormwater.

The Sponge City pilot area in Zhenjiang is a 22 km2 (~8.5 mi2) watershed that includes the urban core of the City. The stormwater management goals for the pilot area included control and treatment of runoff from more frequent storms and to prevent flooding from less frequent, but more intense storms. To meet these goals, the City undertook a significant stormwater and flooding assessment and planning effort. The goals include handling flooding caused by a 30-year return period design storm and capturing 75% of runoff for water quality.

The Solution

A robust stormwater modeling framework was necessary to represent the existing system, including the sewer network, storage, drainage channels, diversion structures, and lift stations. LimnoTech was tasked with developing and improving an urban stormwater drainage model in collaboration with project partners. The model was used to evaluate modifications to system operations, the addition of green infrastructure, and other stormwater management measures and the feasibility of design alternatives.

LimnoTech expanded and further developed an existing SWMM model of the study area based on data obtained from City officials, field visits, and drawings. LimnoTech also advised on monitoring strategies and the implementation of green and grey infrastructure solutions to meet stringent flood reduction and water quality improvement goals.

The SWMM collection system model was linked to a two-dimensional surface flow model to route surcharged flow over the surface of the sloped terrain of Zhenjiang. Using the SWMM model and the linked model framework, the project team developed stormwater management design concepts for green infrastructure and underground storage to support stormwater management solutions and planning to control flooding and improve water quality. The models and concept plan developed can be expanded in the future to site and size green infrastructure and other storage facilities.