教堂山Eastgate洪水淺析：劍指市政府

Understanding Flooding at Eastgate: A Stormwater Lesson from the Booker Creek 

The 3D map of the Booker Creek Watershed in Chapel Hill clearly shows why the Eastgate Shopping Center, located in the southeast corner, has experienced persistent flooding for many years. Urban development has continually added impervious surfaces, which generate more stormwater runoff. This issue has been noticed by both civil engineers and local residents. However, there is a critical factor that is often overlooked, even by professionals, and rarely considered by government officials.

That factor is the stormwater drainage system. These systems are designed to manage rainfall by collecting, transporting, and discharging runoff from roofs, streets, and other surfaces into local water bodies. Ideally, they help prevent flooding and protect property. In Chapel Hill, the performance of the stormwater drainage system is a mixed story.

On one hand, the system does help reduce flooding in upstream areas by quickly channeling water away from streets and buildings through ditches and underground pipes. On the other hand, this efficiency creates a problem downstream. All that water is eventually discharged into tributaries of Booker Creek. Even without a stormwater system, the runoff would still reach the creek. However, under natural conditions, the flow would move much more slowly. Chapel Hill’s landscape is densely wooded, and the forest floor is covered with a thick layer of leaves and organic matter, which absorb water and slow the overland flow.

When stormwater is routed through engineered channels over relatively steep terrain, the speed of flow increases dramatically. This causes rapid accumulation of runoff in Booker Creek. What might have taken an hour to arrive under natural conditions can now reach Eastgate in just ten minutes. This sudden surge in flow volume contributes significantly to flooding, especially because a section of Booker Creek beneath Eastgate was covered over and turned into an underground channel during the construction of the shopping center. If the creek were left open, water might disperse more effectively and cause less damage to nearby neighborhoods. However, in its current form, the floodwater becomes choked at the point where the creek enters the underground section near the US 15/501 bridge.

Are there any solutions to this problem? Potentially, yes. One practical approach is to slow down the speed at which water is routed. This can be done through distributed stormwater retention strategies. For example, the town could encourage residents in upstream areas to install small retention ponds or rain barrels on their properties to temporarily hold water from downspouts. If supported with tax incentives, this grassroots solution could be implemented widely.

Another option is the construction of large municipal retention ponds. This has been discussed by the town, but many residents remain skeptical about the effectiveness and fairness of such projects.

A more fundamental, long-term solution would be to remove the Eastgate Shopping Center entirely and restore the area to its original wetland condition. Building over a creek was a poor planning decision from the start. As long as the creek remains covered and commercial infrastructure sits atop a natural floodplain, flooding will remain an ongoing challenge.

The Eastgate issue is not simply about engineering or changing weather patterns. Even if the climate remained stable, continued urban development upstream would increase runoff and worsen flooding. The real root of the problem lies in past urban planning choices. Blaming climate change shifts attention away from the core issue and delays necessary corrective actions.

In conclusion, the persistent flooding in the Eastgate area is a result of planning decisions, not just natural forces. Addressing the problem requires a rethinking of how cities interact with water. Long-term resilience depends not only on improved infrastructure but also on acknowledging and correcting past mistakes in land use and development.

ChatGPT 翻譯的中文：

位於北卡羅來納州教堂山的布克溪流域三維地圖清晰地展示了為何位於東南角的Eastgate購物中心多年來一直遭遇洪水。城市開發不斷增加不透水表麵，從而產生更多的雨水徑流。雖然這個問題已被土木工程師和當地居民所注意，但有一個關鍵因素往往被忽視，甚至專業人士和政府官員也很少考慮。

這個因素就是雨水排放係統。雨水排放係統的設計目的是收集、運輸並排放從屋頂、街道及其他表麵產生的雨水徑流，最終導入附近的水體。理想情況下，這種係統有助於防止洪水並保護財產。在教堂山，該係統的表現是喜憂參半。

一方麵，該係統確實在上遊區域有效防止了洪水，通過溝渠和地下管道迅速將水從街道和建築物引走。但另一方麵，這種“效率”卻在下遊造成了問題。這些水最終匯入布克溪的支流。即便沒有排水係統，徑流最終也會流入布克溪。但在自然條件下，水流速度會慢得多。教堂山的地貌以森林覆蓋為主，林地上厚厚的落葉和有機質可吸收水分、減緩地表徑流。

而當雨水通過人工設計的排水通道，沿相對陡峭的地形快速流動時，其速度會顯著增加，導致雨水迅速在布克溪匯集。本應在一個小時內緩慢流入的水，現在十分鍾內就能抵達Eastgate。這種流量的突然激增是洪水的一個重要因素。特別是在Eastgate下方的一段布克溪在購物中心建設時被覆蓋並轉為地下通道。如果這段溪流保持開放，水流本可能更好地分散，從而減少對周邊社區的損害。然而在現狀下，洪水在靠近15號/501號高速公路橋附近進入地下通道處形成阻塞。

這個問題有解決方案嗎？可能有。一個可行方法是減緩水流的速度，可以通過分布式的雨水滯留策略來實現。例如，當地政府可以鼓勵上遊居民在自家安裝小型滯留池或雨水桶，用於臨時儲存從屋頂流下的雨水。如果提供稅收激勵，這種“草根式”方案可以廣泛推廣。

另一個選擇是建設大型市政雨水滯留池。這個方案已經被提上議程，但許多居民對其效果和公平性仍持懷疑態度。

更根本且長遠的解決方案是徹底拆除Eastgate購物中心，並將該地區恢複為原始濕地。在溪流上建商業設施從一開始就是錯誤的城市規劃決定。隻要溪流仍被覆蓋，商業建築仍占據天然泛濫平原，洪水問題就不會消失。

Eastgate的問題不僅僅是工程設計或天氣變化的問題。即使氣候保持穩定，上遊城市開發的持續推進也會帶來更多徑流並加劇洪水。真正的根源在於過去的城市規劃失誤。將問題歸咎於氣候變化，隻會掩蓋根本矛盾，拖延必要的修正行動。

總之，Eastgate地區持續的洪水並非完全由自然原因造成，而是源自人為的規劃失誤。要解決這一問題，城市必須重新思考與水的關係。要實現長期的韌性發展，不僅需要改進基礎設施，更需要正視並糾正以往在土地使用和開發上的錯誤。