Abstract
Worldwide, urban rivers suffer various degrees of ecological degradation. Rehabilitating heavily modified urban rivers requires holistic approaches, including environmental flow management. We examine the case of Lower Yongding River, Beijing’s mother river, which had dried up since the 1980s and is undergoing a flow replenishment experiment, receiving 342 million m3 of water during 2019–2020 for ecosystem enhancement. Considering the massive cost of replenishment, we address the urgent need to evaluate its outcomes and inform future management through an interdisciplinary modeling approach under the circumstance of severe data shortage. We simulated the study reach’s landscape evolution under five flow scenarios and assessed their ecological effects using the CAESAR-Lisflood model and habitat suitability index method. Despite overall minor morphological differences across scenarios, individual reaches presented pronounced physical changes. Higher-flow scenarios shaped a distinct channel in certain reaches, but historic channel modifications by mining and farming caused minimal responses in others. Additionally, higher-flow scenarios generally created larger and more evenly distributed habitat areas but showed a low payback given the higher flow volumes needed. Targeted channel-floodplain geomorphological restoration is essential for flows to generate desired ecological outcomes. The demonstrated modeling framework offers great promise, informing future rehabilitation actions for heavily modified urban streams.
Highlights
Due to a long agricultural history and rapid urban development in recent decades, most rivers in China, both urban and rural, are severely degraded [1]
We applied the CAESAR-LISFLOOD-FP model version 1.9j to simulate long-term landscape evolution under four environmental flow scenarios identified from step 1 and compared them with the flow replenishment plan proposed by the Beijing Water Science and Technology Institute (BWSTI)
First, the five flow scenarios showed minor differences in metrics such as monthly average wetted area, average surface water width in summer, water depth and flow velocity distributions, and bed level changes, cross-scenario variations were more pronounced in specific reaches, where high- instead of low-flow scenarios were able to shape a distinct channel
Summary
Due to a long agricultural history and rapid urban development in recent decades, most rivers in China, both urban and rural, are severely degraded [1]. Flow reduction and scarcity due to excessive abstraction, in-stream and floodplain mining, channel modifications, floodplain development, and pollution have fundamentally altered ecosystem structure and function, rendering many rivers ecologically and physically unrecognizable [4]. What is more, these challenges are likely to be exacerbated by future economic development and climate change, in water-stressed northern China [5].
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