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 翻译的中文：
位于北卡罗来纳州教堂山的布克溪流域三维地图清晰地展示了为何位于东南角的Eastgate购物中心多年来一直遭遇洪水。城市开发不断增加不透水表面，从而产生更多的雨水径流。虽然这个问题已被土木工程师和当地居民所注意，但有一个关键因素往往被忽视，甚至专业人士和政府官员也很少考虑。
这个因素就是雨水排放系统。雨水排放系统的设计目的是收集、运输并排放从屋顶、街道及其他表面产生的雨水径流，最终导入附近的水体。理想情况下，这种系统有助于防止洪水并保护财产。在教堂山，该系统的表现是喜忧参半。
一方面，该系统确实在上游区域有效防止了洪水，通过沟渠和地下管道迅速将水从街道和建筑物引走。但另一方面，这种“效率”却在下游造成了问题。这些水最终汇入布克溪的支流。即便没有排水系统，径流最终也会流入布克溪。但在自然条件下，水流速度会慢得多。教堂山的地貌以森林覆盖为主，林地上厚厚的落叶和有机质可吸收水分、减缓地表径流。
而当雨水通过人工设计的排水通道，沿相对陡峭的地形快速流动时，其速度会显著增加，导致雨水迅速在布克溪汇集。本应在一个小时内缓慢流入的水，现在十分钟内就能抵达Eastgate。这种流量的突然激增是洪水的一个重要因素。特别是在Eastgate下方的一段布克溪在购物中心建设时被覆盖并转为地下通道。如果这段溪流保持开放，水流本可能更好地分散，从而减少对周边社区的损害。然而在现状下，洪水在靠近15号/501号高速公路桥附近进入地下通道处形成阻塞。
这个问题有解决方案吗？可能有。一个可行方法是减缓水流的速度，可以通过分布式的雨水滞留策略来实现。例如，当地政府可以鼓励上游居民在自家安装小型滞留池或雨水桶，用于临时储存从屋顶流下的雨水。如果提供税收激励，这种“草根式”方案可以广泛推广。
另一个选择是建设大型市政雨水滞留池。这个方案已经被提上议程，但许多居民对其效果和公平性仍持怀疑态度。
更根本且长远的解决方案是彻底拆除Eastgate购物中心，并将该地区恢复为原始湿地。在溪流上建商业设施从一开始就是错误的城市规划决定。只要溪流仍被覆盖，商业建筑仍占据天然泛滥平原，洪水问题就不会消失。
Eastgate的问题不仅仅是工程设计或天气变化的问题。即使气候保持稳定，上游城市开发的持续推进也会带来更多径流并加剧洪水。真正的根源在于过去的城市规划失误。将问题归咎于气候变化，只会掩盖根本矛盾，拖延必要的修正行动。
总之，Eastgate地区持续的洪水并非完全由自然原因造成，而是源自人为的规划失误。要解决这一问题，城市必须重新思考与水的关系。要实现长期的韧性发展，不仅需要改进基础设施，更需要正视并纠正以往在土地使用和开发上的错误。
