A Study of Temporal Variations of Groundwater Level, Recharge, and Baseflow: Does Scaling Exist in These Processes?

降水补给(R)和底流补给(BF)是流域尺度水循环的两个主要过程。这些过程随着时间和空间的不同而变化。水资源的有效管理需要对这些过程有深刻的理解。然而，由于缺乏数据或测量R和BF的困难，我们目前对这些复杂过程的认识和理解非常有限，特别是关于它们的时间和空间变化。已有的研究对R的空间变化作了各种假设，而对R和BF的时间变化关注较少。虽然很难测量R和BF，但测量观测井水位(H)和河流径流相对容易。在几年或几十年的不同时间间隔内采集的大量地下水位数据往往是可用的。地表水系统中地下水位的波动是系统对补给和排泄的动态响应，包含了大量的补排信息。对艾奥瓦州核桃溪流域7口监测井水位的初步分析表明，地下水位的波动是一个时间分形，其分维D在空间上是变化的。该流域和其他4个流域的基流也表现为时间分维，更重要的是具有尺度突变。我们的目标是：1)确定地下水位和基流的分形标度的存在及其与补给的关系；2)找出分形标度背后的物理原因；3)研究含水层物理非均质性对地下水位、补给和流量波动及其标度的影响，以及4)地下水补给过程的性质。这些目标将通过检验六个假设来实现。这些假设将通过在USGG网站上收集和分析6个地下水区域的42个监测井的长期地下水位测量和11个水文单元的58个测站50-100年的径流，并通过进行综合水文建模(IHM)、随机分析和数值模拟来验证。通过数据挖掘，我们将使用美国地质调查局多年来收集的大量数据来识别时间尺度的存在。使用IHM，我们将能够评估P、ET和？的时空变化的影响。关于h和bf的波动。通过随机分析和数值模拟，我们将研究含水层物理性质的空间变化对h和bf的时间变化及其标度的影响，以及R过程的性质。这项研究最重要的优点是发现了手部高炉的时间尺度，并提供了尺度背后的物理原因。H的时间尺度可能在许多含水层中普遍存在，正如我们在本提案中通过14个USGS井的最长水位数据的光谱所表明的那样。对于这种尺度，可能有一个简单的解释：地下水位的波动是由各种贡献水文变量(例如，P、ET和？)引起的。具有不同的时间和/或空间尺度。因此，头部波动中没有特有的时间尺度！我们急于做进一步的调查。自然界中的过程是否依赖于它们运行的规模是水文科学的主要问题之一。(Sposito，1998)。自从尺度不变性作为指导数据分析和建模方法的基础以来，水文学中的尺度研究一直是一个重要的研究方向(NRC，1991)。在过去的十年中，水文学在寻找空间尺度不变性方面取得了重大进展。然而，对地下水水文变量的时间尺度关注较少。我们提出了一个相对较新的随机研究方向，正如专家小组在最初提案中所总结的那样，并试图在随机方法的应用方面向前迈进一步。广泛的影响包括：1)使用丰富的地下水位和径流数据试图了解h和bf的时间变化模式，使拟议的研究方法和结果具有广泛的适用性；2)拟议的研究与NSF倡议密切相关：水循环研究；3)本研究所获得的知识是水资源的长期管理和规划以及应对气候变化所必需的；4)一名在读的博士生正在研究这一主题。如果提案获得资助，两名新生(一名研究生和一名本科生)将参与这个项目。5)这项研究预计会发表几篇论文，因为根据我们的初步结果，已经写了两篇论文(一篇发表，另一篇最近提交)。最后，我们想说的是，解决评审员和专家小组对提案原稿和第二稿的评论极大地改进了提案。

0510322ZhangGroundwater recharge (R) from precipitation and discharge to rivers as baseflow (BF) are two of the mainprocesses in the basin-scale water cycle. These processes vary with time and space. Effective managementof water resources requires deep understanding of these processes. Due to the lack of data or thedifficulties in measuring R and BF, however, our current knowledge and understanding of these complexprocesses are very limited, especially about their temporal and spatial variations. Various assumptions aremade about spatial variations of R in existing studies and little attention has been given to temporalvariations of R and BF. While it is difficult to measure R and BF, it is relatively easy to measure the waterlevels in observation wells (h) and runoff in rivers. Extensive groundwater level data sampled at varioustime intervals over periods of years or decades are often available. Fluctuations of the water table in agroundwater system are dynamic responses of the system to its recharge and discharge, and thus containsignificant amount of information about the recharge and discharge. Our preliminary analyses of theobserved water levels in seven monitoring wells at the Walnut Creek watershed of Iowa indicate thatfluctuations of the groundwater levels is a temporal fractal whose fractal dimension (D) varies spatially.Baseflow from this and other four watersheds also behaves as a temporal fractal and, more importantly,has a transition time or break in scaling.Our objectives are: 1) to determine existence of fractal scaling of groundwater level and baseflow andtheir relationship with recharge; 2) to identify physical causes behind fractal scaling; 3) to study the effectsof aquifers' physical heterogeneity on fluctuations of groundwater level, recharge, and discharge and ontheir scaling, and 4) to investigate the nature of groundwater recharge process. These objectives will bereached by testing six hypotheses. These hypotheses will be tested by collecting and analyzing the longtermgroundwater level measurements in 42 monitoring wells in 6 groundwater regions and thestreamflow at 58 gauge stations in 11 hydrological units over a period of 50 - 100 years at the USGGwebsite, and by conducting an integrated hydrologic modeling (IHM), stochastic analyses, and numericalsimulations. With data mining we will use the extensive data collected by USGS over the years to identifythe existence of the temporal scaling. With IHM we will be able to assess impacts of temporal and spatialvariations of P, ET, and ? on fluctuations of h and BF. With stochastic analyses and numericalsimulations, we will investigate effects of spatial variations of aquifers' physical properties on thetemporal variations of h and BF and their scaling as well as the nature of R process.The intellectual merits. The most important merits of this research are to find the temporal scaling of hand BF and to provide physical causes behind the scaling. Temporal scaling of h may be pervasive inmany aquifers as we show in this proposal by the spectra of the longest water level data in 14 USGS wells.There may be a simple explanation for the scaling: fluctuations of groundwater levels are due to variouscontributing hydrological variables (e.g., P, ET, and ?) with differing time and/or spatial scales. As aresult, there is no characteristic time scale in the head fluctuations! We are anxious to do furtherinvestigation. Whether processes in the natural world are dependent or independent of the scale at whichthey operate is one of the major issues in hydrologic science . (Sposito, 1998). There has been a significanteffort in searching for scaling in hydrology since an invariance property across scales as a fundamentalshould guide data analysis and modeling methods (NRC, 1991). Significant progresses in searching spatialscale invariance have been made during the last decade in hydrology. However, less attention was given totemporal scaling of subsurface hydrological variables. We have proposed a relatively new direction ofstochastic research, as summarized by the panel on the original proposal, and are trying to make a forwardstep in application of stochastic approaches. The broad impacts include: 1) use of abundant groundwaterlevel and streamflow data in trying to understand the patterns of temporal variations of h and BF make themethods and results of the proposed research widely applicable, 2) the proposed research is closely relatedto the NSF initiative: Water Cycle Research, 3) the knowledge obtained in this research is needed in longtermmanagement and planning of water resources and in dealing with climate changes, 4) A current Ph.D.student is working on this topic. Two new students (one graduate and one undergraduate) will participatein this project if the proposal is funded, 5) Several publications are expected from this research as twopapers have been written (one published and another submitted recently) based on our preliminary results.Finally, we want to say that addressing the comments made by the reviewers and panel on the original andsecond-submission of this proposal has greatly improved the proposal.