Water Resources Research

Ishizuka, Masahide; Sone, Yumi; Ii, Hiroyuki; Hirata, Tatemasa

doi: 10.1029/2004WR003810pmid: N/A

Mesoscale spatial distributions and temporal variations of oxygen and hydrogen isotope compositions in surface waters were observed on the Kii Peninsula, Japan, which receives more than 3000 mm of precipitation annually. The enriched isotopic values were distributed along the western, southern, and eastern coasts. To explain this, we proposed a new parameter, early dropped rainwater frequency (ERF), and defined it as the number of times that early dropped rainwater was first observed in a domain. ERF can be considered a characteristic of rainfall, and it is a useful parameter for clarifying mesoscale isotopic distribution. A mass balance simulation suggested the early dropped rainwater determined the specific isotopic value of stream water in a watershed.

Kerachian, Reza; Karamouz, Mohammad

doi: 10.1029/2005WR004575pmid: N/A

In this study, an algorithm combining a water quality simulation model and a deterministic/stochastic conflict resolution technique is developed for determining optimal reservoir operating rules. As different decision makers and stakeholders are involved in reservoir operation, the Nash bargaining theory is used to resolve the existing conflict of interests. The utility functions of the proposed models are developed on the basis of the reliability of the water supply to downstream demands, water storage, and the quality of the withdrawn water. The expected value on the Nash product is considered as the objective function of the stochastic model, which can incorporate the inherent uncertainty of reservoir inflow. A water quality simulation model is also developed to simulate the thermal stratification cycle and the reservoir discharge quality through a selective withdrawal structure. The optimization models are solved using a new version of genetic algorithms called varying chromosome length genetic algorithm (VLGA). In this algorithm the chromosome length is sequentially increased to provide a good initial solution for the final traditional GA‐based optimization model. The proposed stochastic optimization model can also reduce the computational burden of the previously proposed models such as stochastic dynamic programming (SDP) by reducing the number of state transitions in each stage. The proposed models which are called VLGAQ and SVLGAQ are applied to the 15‐Khordad Reservoir in the central part of Iran. The results show that the proposed models can reduce the salinity of allocated water to different water demands as well as the salinity buildup in the reservoir.

Genius, Margarita; Tsagarakis, Konstantinos P.

doi: 10.1029/2005WR004833pmid: N/A

This paper analyses the extent to which households in an urban area are willing to pay to ensure a fully reliable water supply when the latter induces changes in drinking water quality. The water supply system in the city of Heraklion, Greece, is characterized by periodic water rationing, which is more pronounced in the summer months. The generalized use of cisterns and even water tanks helps residents cope with quantity shortages but has a negative effect on the quality of the water reaching their taps. The results of our contingent valuation show that respondents not affected by shortages and already drinking tap water have a smaller willingness to pay, while positive perceptions on quality have a positive effect.

Winsemius, H. C.; Savenije, H. H. G.; van de Giesen, N. C.; van den Hurk, B. J. J. M.; Zapreeva, E. A.; Klees, R.

doi: 10.1029/2006WR005192pmid: N/A

The temporal signature of terrestrial storage changes inferred from the Gravity Recovery and Climate Experiment (GRACE) has been assessed by comparison with outputs from a calibrated hydrological model (lumped elementary watershed (LEW)) of the upper Zambezi and surroundings and an inspection of the within‐month ground track coverage of GRACE together with spatial‐temporal rainfall patterns. The comparison of the hydrological model with GRACE reveals temporal inconsistencies between both data sets. Because the LEW model has been calibrated and validated with independent data sources, we believe that this is a GRACE artifact. The within‐month ground track coverage shows an irregular orbit behavior which may well cause aliasing in the GRACE monthly deconvolutions. This aliasing is the most probable cause of observed temporal inconsistencies between GRACE and other data sets.

Rupp, David E.; Selker, John S.

doi: 10.1029/2006WR005080pmid: N/A

The method of recession analysis proposed by Brutsaert and Nieber (1977) remains one of the few analytical tools for estimating aquifer hydraulic parameters at the field scale and beyond. In the method, the recession hydrograph is examined as −dQ/dt = f(Q), where Q is aquifer discharge and f is an arbitrary function. The observed function f is parameterized through analytical solutions to the one‐dimensional Boussinesq equation for unconfined flow in a homogeneous and horizontal aquifer. While attractive in its simplicity, as originally presented it is not applicable to settings where slope is an important driver of flow, or where hydraulic parameters vary greatly with depth. We compare analytical solutions to the linearized one‐dimensional Boussinesq equation for a sloping aquifer to numerical solutions of the full nonlinear equation. The behavior of the nonlinear Boussinesq equation is also assessed when the aquifer is heterogeneous wherein the lateral saturated hydraulic conductivity k varies as a power law with height z above the impermeable layer (k ∼ zn, n constant ≥ 0). All of the analytical solutions differ in key aspects from the nonlinear solution when plotted as −dQ/dt = f(Q) and thus are inappropriate for a Brutsaert and Nieber‐type analysis. However, new analytical solutions for a sloping aquifer are derived “empirically” from the numerical simulations that are applicable during the late period of recession when the recession curve converges to −dQ/dt = aQb, where b = (2n + 1)/(n + 1) and a is a function of the dimensions and hydraulic properties of the aquifer.

Cortis, Andrea; Harter, Thomas; Hou, Lingling; Atwill, E. Robert; Packman, Aaron I.; Green, Peter G.

doi: 10.1029/2006WR004897pmid: N/A

Complex transport behavior other than advection‐dispersion, simple retardation, and first‐order removal has been observed in many biocolloid transport experiments in porous media. Such nonideal transport behavior is particularly evident in the late time elution of biocolloids at low concentrations. Here we present a series of saturated column experiments that were designed to measure the breakthrough and long‐term elution of Cryptosporidium parvum in medium sand for a few thousand pore volumes after the initial source of oocysts was removed. For a wide range of ionic strengths, I, we consistently observe slower‐than‐Fickian, power law tailing. The slope of the tail is flatter for higher I. At very high ionic strength the slope decays to a rate slower than t−1. To explain this behavior, we propose a new filtration model based on the continuous time random walk (CTRW) theory. Our theory upscales heterogeneities at both the pore‐scale geometry of the flow field and the grain surface physicochemical properties that affect biocolloid attachment and detachment. Pore‐scale heterogeneities in fluid flow are shown to control the breakthrough of a conservative tracer but are shown to have negligible effect on oocyst transport. In our experiments, C. parvum transport is dominated by the effects of physicochemical heterogeneities. The CTRW model provides a parsimonious theory of nonreactive and reactive transport. The CTRW filtration process is controlled by three parameters, Λ, β, and c, which are related to the overall breakthrough retardation (R = 1 + Λ), the slope of the power law tail (β), and the transition to a slower than t−1 decay (c).

Turner, Ned B.; Ryan, Joseph N.; Saiers, James E.

doi: 10.1029/2006WR004972pmid: N/A

To examine the importance of desorption kinetics to colloid‐facilitated transport, we conducted column experiments comparing the transport of cesium and strontium through a saturated quartz sand porous medium in the absence and presence of illite colloids at two ionic strengths. Because cesium desorption from illite was anticipated to be slower than that of strontium, we expected to see a contrast in the colloid‐facilitated transport of the cations. A model of colloid‐facilitated transport accounting for second‐order cation adsorption to and desorption from the quartz, second‐order cation adsorption to and desorption from fast and slow sites on the illite colloids, and second‐order colloid deposition to and release from the quartz accurately simulated the cation transport in the absence and presence of the illite colloids. The column results and model simulations revealed that cesium desorption was indeed slower than strontium desorption and that this contrast in desorption kinetics resulted in greater colloid‐facilitated transport of the cesium. The desorption of both cations was slow relative to the rate of advection. The fast and slow sites on the illite colloids behaved like planar and frayed edge sites typically identified for cesium adsorption to illite. The amount of cesium adsorbed to the slow, or frayed edge, sites was similar to the frayed edge site density of illite estimated by other researchers.

Ochiai, Naoyuki; Kraft, Erika L.; Selker, John S.

doi: 10.1029/2006WR004961pmid: N/A

Prediction of colloid transport in the subsurface is relevant to researchers in a variety of fields such as contaminant transport, wastewater treatment, and bioremediation. Investigations have traditionally relied on column studies whereby mechanistic inferences must be drawn on the basis of colloid behavior at the outlet. Over the past decade, development of noninvasive visualization techniques based on visible light, magnetic resonance, and X rays have provided insight into a number of colloid transport mechanisms by enabling direct observation of individual colloids at the pore scale and colloid concentrations at longer length scales. As research focus shifts from transport of ideal colloids in ideal media such as glass beads to natural colloids in natural porous media, these noninvasive techniques will become increasingly useful for studying the collection of mechanisms at work in heterogeneous pore systems. It is useful at this juncture to review recent progress in colloid transport visualization as a starting point for further development of visualization tools to support investigation of colloids in natural systems. We briefly discuss characteristics of visualization systems currently used to study colloid transport in porous media and review representative microscale and mesoscale visualization studies conducted over the past decade, with additional attention given to two optical visualization systems being developed by the authors.

Osenbrück, Karsten; Fiedler, Stefan; Knöller, Kay; Weise, Stephan M.; Sültenfuß, Jürgen; Oster, Harald; Strauch, Gerhard

doi: 10.1029/2006WR004977pmid: N/A

Nitrate pollution from agricultural activities often persistently affects groundwater quality due to long residence times in the vadose and saturated zone. In this study we used a lumped parameter approach to estimate the residence time of groundwater and nitrate from the agriculturally used Jahna‐Aue drinking water catchment in Saxonia, Germany. Inverse modeling of measured concentrations of tritium and tritiogenic 3He revealed consistent mean residence times between 25 and 50 years for the young, nitrate‐rich groundwater component, and high contributions (>75%) of an old, tracer‐free, and nitrate‐poor groundwater. The obtained age distributions are in accordance with the complex hydrogeological situation of the investigated catchment, suggesting that the shallow and therefore most vulnerable part of the aquifer is not connected to the production wells. High residence times are supported by low concentrations of CFCs and by radiogenic 4He as an independent age indicator. CFC concentrations only yield lower age limits due to identified problems with CFC contamination. Using the tracer‐calibrated age distributions, future nitrate concentrations in the production wells most probably will remain below the drinking water limit because of the high dilution with old, nitrate‐poor groundwater. Deterioration of the groundwater quality with respect to nitrate may occur if the groundwater pumping regime is changed so that the fraction of the younger, nitrate‐bearing water is increased.

Baumann, Thomas; Niessner, Reinhard

doi: 10.1029/2006WR004893pmid: N/A

Colloids are considered as potential carriers of otherwise immobile contaminants. In this framework the contaminant‐colloid interaction is assumed to be permanent, or the contaminant release from the colloids is not explicitly assessed. In this study, we report on micromodel experiments to visualize and quantify the behavior of colloids in a chemically reactive environment. Fluorescent polystyrene latex beads were injected into a micromodel pore network containing water, air, and 1‐octanol. The colloids were found to attach to the hydrophobic 1‐octanol phase with slightly higher attachment rates compared to the solid interface. Colloids attached to the 1‐octanol sometimes disintegrated because of a swelling of the polystyrene polymer. The hydrophobic fluorescent dye was then found to partition into the 1‐octanol. While the 1‐octanol droplets were slowly dissolving, the fluorescent dye was staying in the droplet at first. At high concentrations and very small droplets the dye was dissolving with 1‐octanol. Although one might be tempted to neglect the repartitioning of contaminants from colloids to other phases because of a limited mass of colloid associated contaminants, this effect has to be included into colloid transport models at contaminated sites with nonaqueous phase liquids, which are more attractive to the contaminant than the colloid or which change the stability of the colloid.