Abstract

To date, environmental flow strategies have predominantly been used in cases where a lack of available water has degraded the ecological quality and natural functioning of a river system. In this study, we used environmental flows on an urbanized watershed where flow volumes and flow rates have increased, and large (e.g. 100-year) event return periods become more frequent (∼10 years). Using an environmental flows strategy to model the amount of hydrological alteration, we assessed whether urban development and land cover changes have impacted the flow regime and the ecological health of this watershed. We reconstructed the flow regime at Lovers Creek (Barrie, Ontario, Canada) using three scenarios of urban development: a pre-settlement reference condition with 100% natural cover, mid-development with 6% urban cover and the current condition with 21% urban cover. We found that, in contrast to many other studies, increased urban cover has coincided with increased baseflow volumes, as well as increased volumes in other components of the flow regime. Of particular concern were the increased flow rate and volume of large events such as channel forming and riparian flows; an increased rate of change in event hydrographs, and a much shorter return period of large event storms (e.g. a 100-year event under reference conditions, is now a 10-year event in the current urbanized condition). In this watershed, restoration of flow to the reference condition is not practical; however, using improved stormwater management such as low-impact development technologies and green infrastructure may offset some of the alteration to the flow regime and mitigate future further alterations due to increased urbanization. As Lovers Creek has been identified as a critical coldwater stream habitat with brook trout, the results of this study are being used to assess changes in the ecological health due to increased urban cover, and to develop management strategies that assist in restoring a more natural flow regime in order to better protect both natural habitats and human infrastructure that are vulnerable to flooding caused by more frequent, increased volume flow events.

摘要

迄今为止，环境流量策略主要用于缺乏可用水导致河流系统的生态质量和自然功能退化的情况。在这项研究中，我们在城市化流域使用环境流量，其中流量和流速增加，大型（例如 100 年）事件重现期变得更加频繁（~10 年）。使用环境流量策略来模拟水文变化的数量，我们评估了城市发展和土地覆盖变化是否影响了该流域的流量状况和生态健康。我们使用三种城市发展情景重建了 Lovers Creek（加拿大安大略省巴里）的流态：具有 100% 自然覆盖率的沉降前参考条件，6% 城市覆盖率的中期开发和 21% 城市覆盖率的现状。我们发现，与许多其他研究相比，城市覆盖的增加与基流体积的增加以及流态其他组成部分的体积增加同时发生。特别值得关注的是增加的流量和大型事件的数量，例如通道形成和河岸流；事件水文过程线的变化率增加，大事件风暴的重现期要短得多（例如，参考条件下的 100 年事件，现在是当前城市化条件下的 10 年事件）。在这个流域，将流量恢复到参考条件是不切实际的；然而，使用改进的雨水管理，如低影响开发技术和绿色基础设施，可能会抵消部分流量状态的改变，并减轻未来因城市化进程的增加而导致的进一步改变。由于 Lovers Creek 已被确定为鳟鱼重要的冷水溪流栖息地，因此本研究的结果正用于评估因城市覆盖增加而导致的生态健康变化，并制定有助于恢复更自然水流的管理策略以更好地保护自然栖息地和人类基础设施，这些自然栖息地和人类基础设施容易受到更频繁、增加的体积流量事件引起的洪水的影响。