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

降水补给地下水和以基流形式排入河流是流域水循环的两个主要过程。这些过程随时间和空间而变化。有效的水资源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知识和理解非常有限，特别是关于它们的时间和空间变化。现有研究对R的空间变化作了各种假设，对R和BF的时间变化关注较少。R和BF的测量比较困难，而观测井水位(h)和河流径流量的测量相对容易。在几年或几十年的不同时间间隔取样的大量地下水位数据通常是可用的。地下水位波动是地下水系统对补给和排放的动态响应，包含了大量补给和排放的信息。本文对爱荷华州核桃溪流域7口监测井的观测水位进行了初步分析，结果表明，地下水位波动具有时间分形特征，其分形维数(D)具有空间差异。来自这个流域和其他四个流域的基流也表现为时间分形，更重要的是，在尺度上有一个过渡时间或中断。我们的目标是：1)确定地下水位和基流是否存在分形标度及其与补给的关系；2)找出分形结垢背后的物理原因；3)研究含水层物理非均质性对地下水位、补给、排放波动及其结垢的影响；4)探讨地下水补给过程的性质。这些目标将通过测试六个假设来实现。这些假设将通过收集和分析6个地下水区域42个监测井的长期地下水位测量数据和usgg.com上11个水文单元58个测量站50 - 100年期间的流量数据，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勘探局多年来收集的大量数据来确定时间尺度的存在。利用IHM，我们将能够评估P、ET和？ ？的时空变化的影响。h和BF的波动。通过随机分析和数值模拟，研究了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。智力上的优点。本研究最重要的优点是找到手BF的时间结垢，并提供结垢背后的物理原因。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口美国地质勘探局井中最长水位数据的光谱所显示的那样。对标度可能有一个简单的解释：地下水水位的波动是由于不同时间和/或空间尺度的各种水文变量（如P、ET和？）造成的。因此，在头部波动中没有特征时间尺度！我们急于做进一步的调查。自然界中的过程是依赖还是独立于其运行的尺度是水文学的主要问题之一。(Sposito, 1998)。由于跨尺度的不变性是指导数据分析和建模方法的基本属性，因此在寻找水文尺度方面已经做出了重大努力（NRC, 1991）。近十年来，水文学在寻找空间尺度不变性方面取得了重大进展。然而，对地下水文变量的时间尺度研究较少。我们提出了一个相对较新的随机研究方向，正如原提案小组所总结的那样，并试图在随机方法的应用方面迈出一步。广泛的影响包括：1)利用丰富的地下水位和河流流量数据，试图了解h和BF的时间变化模式，使所提出的研究方法和结果具有广泛的适用性；2)所提出的研究与NSF倡议密切相关；水循环研究，3)研究中获得的知识对水资源的长期管理和规划以及应对气候变化是需要的，4)目前有一名博士生正在研究这个课题。2名新生（1名研究生和1名本科生）如果获得资助，将参与该项目。5)根据我们的初步研究结果，本研究预计将发表两篇论文（一篇已发表，另一篇最近提交）。最后，我们想说的是，解决了审稿人和专家组对该提案最初和第二次提交的意见，大大改进了该提案。

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.