Dynamic Response of Watershed Subsurface System to Extreme Rainfall Events

2013年9月，科罗拉多前线山脉（英语：Front Range）的暴雨导致该地区大范围洪水泛滥。虽然洪水在几天内退去，但地下水的数据表明，洪水过后很长一段时间，地下水的储存量发生了重大变化。这项研究旨在了解地下水储存的变化，以应对极端降雨事件。了解极端降雨事件的影响，可以为预测更长时间和更大空间尺度的综合影响提供基础。通过评估浅层土壤和深层含水层作为洪水自然储存的潜力，这项研究可以为水管理人员提供科学依据，以评估极端降雨事件期间储存的多余水，并在释放回溪流时及时利用资源。该项目将有大量的教育内容。研究生将直接参与研究。为期两周的本科实地课程将纳入本研究提出的一些原位含水层测试。一个地下水流计算机模型将被创建为一个本科建模类项目。这些领域和建模计划将使大约90名本科生受益，并为他们提供学习实用技能和水科学真实的研究经验的机会。该项目计划还包括通过RESESS计划从代表性不足的群体中招募学生并与他们合作，RESESS计划是NSF支持的暑期实习计划，致力于增加进入地球科学的学生的多样性。 本研究的总体目标是更好地了解流域尺度地下水文系统对极端降雨事件的动态响应。具体的研究问题是：（1）在极端降雨条件下，有多少降水能渗入包气带？(2)在极端降雨的情况下，地下水储存量会发生多大变化？(3)极端天气对地下系统的影响在时间和空间上会达到什么程度？研究计划由三部分组成。首先是收集和分析水文数据，这些数据将为系统的概念化和模型校准的参数提供信息。二是进行现场和实验室测量，表征包气带和饱和带的水文特性。第三个是开发一个综合的渗流区和饱和区流动模型，以综合数据，检验假设，并解决研究问题。科罗拉多博尔德西部的上博尔德溪将被用作试验床，因为现有的水文数据跨越了极端降水期前后的可用性。使用物理为基础的质量平衡的方法，这项研究提供了一个定量的建模框架，连接降水，地下水流量，并在流域尺度的流基流，强调严格的渗流区的渗透过程建模。这项研究将揭示新的光渗透到包气带，地下水存储的动态变化，以及时间和空间的范围内，流域地下系统可能会受到极端降雨事件的影响。研究地点包括不同的地质和地理，使结果可转移到其他地区。本研究将利用最新的模拟能力和利用数据的可用性，推进包气带和饱和带综合流动的模拟。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

The episodes of torrential rainfall in September 2013 in the Colorado Front Range caused widespread flooding in the area. While floodwater receded within days, data from subsurface suggested substantial changes in groundwater storage long after the flood. This study seeks to understand the changes in groundwater storage in response to extreme rainfall events. Understanding the effects of extreme rainfall events can provide the basis for predicting aggregated effects over longer temporal and larger spatial scales. By assessing the potential for shallow soils and deeper aquifers to serve as natural storages for floodwaters, this study could provide a scientific basis for water managers to assess the excess water stored during extreme rainfall events and timely utilize the resource when it is released back to streams. The project will have a substantial educational element. Graduate students will be directly involved in research. A two-week undergraduate field course will incorporate some in-situ aquifer tests proposed for this study. A groundwater flow computer model will be created for an undergraduate modeling class project. These field and modeling plans will benefit approximately 90 undergraduate students and offer them the opportunity to learn practical skill sets and a real research experience in water sciences. The project plan also includes recruiting and working with students from underrepresented groups through the RESESS program, an NSF supported summer internship program dedicated to increasing the diversity of students entering geosciences. The overall goal of this research is to better understand the dynamic response of watershed-scale subsurface hydrologic systems to extreme rainfall events. The specific research questions are: (1) How much could precipitation infiltrate into the vadose zone during extreme rainfalls? (2) How much does the subsurface water storage change in the event of extreme rainfall? (3) To what temporal and spatial extent could extreme rainfalls impact subsurface systems? The research plan consists of three components. The first is to collect and analyze hydrologic data that will provide information for conceptualizing the system and the parameters for model calibration. The second is to conduct in-situ and laboratory measurements to characterize the hydrologic properties of the vadose zone and the saturated zone. The third is to develop an integrated vadose-zone and saturated-zone flow model to synthesize data, test hypotheses, and address research questions. The Upper Boulder Creek west of Boulder, Colorado, will be utilized as a test bed because of the availability of existing hydrologic data spanning over the pre- and post-extreme precipitation periods. Using a physics-based mass-balance approach, this study offers a quantitative modeling framework that links precipitation, subsurface flow, and stream baseflow at watershed scales, with an emphasis on rigorous modeling of infiltration processes in the vadose zone. This study will shed new light on infiltration into the vadose zone, dynamic changes in subsurface water storage, and the temporal and spatial extent that a watershed subsurface system could be affected under extreme rainfall events. The study site includes varying geology and geography, making the results transferrable to other regions. This study will advance modeling integrated vadose zone and saturated zone flow through utilizing latest modeling capability and taking advantage of data availability. On the basis of its contribution to rigorous modeling infiltration and site transferability, this study is potentially transformative.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.