Episodic and Continuous Recharge Estimation from High-Resolution Well Records

Water table fluctuation (WTF) methods are a primary and well-established way to determine groundwater recharge based on the direct response of the water table to precipitation input. An emerging complexity of recharge is whether it occurs as an episodic and transient process, or a continuous steady-state process, however, most studies have not focused on these short-term vs. long-term timescales, in part because of a lack of data resolution. Here, high-resolution (subhourly) precipitation and water-level data are analyzed for wells in the suburbs of New York City using two contrasting WTF approaches, with a common mathematical basis, that are suited to episodic and continuous processes. The resulting hourly recharge results, like the individual water-level records from comparable wells, are sensitive indicators of subtle differences in aquifer conditions such as thickness of the unsaturated zone, position in the flow system and localized preferential flow. While the episodic, transient approach excludes diffuse recharge by design, the continuous, steady-state approach is influenced by short-term precipitation events, and therefore integrates transient processes to some extent. However, the continuous, steady-state approach is subject to its own limitations relating to position in the aquifer system, and may overestimate recharge if aquifer conditions are not well understood. More widespread use of higher resolution data as well as understanding aquifer conditions and refining aquifer parameters would improve WTF recharge estimation.     

Improved Recharge Estimation from Portable,Low‐Cost Weather Stations

Groundwater recharge estimation is a critical quantity for sustainable groundwater management. The feasibility and robustness of recharge estimation was evaluated using physical‐based modeling procedures, and data from a low‐cost weather station with remote sensor techniques in Southern Abbotsford, British Columbia, Canada. Recharge was determined using the Richards‐based vadose zone hydrological model, HYDRUS‐1D. The required meteorological data were recorded with a HOBO^TM weather station for a short observation period (about 1 year) and an existing weather station (Abbotsford A) for long‐term study purpose (27 years). Undisturbed soil cores were taken at two locations in the vicinity of the HOBO^TM weather station. The derived soil hydraulic parameters were used to characterize the soil in the numerical model. Model performance was evaluated using observed soil moisture and soil temperature data obtained from subsurface remote sensors. A rigorous sensitivity analysis was used to test the robustness of the model. Recharge during the short observation period was estimated at 863 and 816 mm. The mean annual recharge was estimated at 848 and 859 mm/year based on a time series of 27 years. The relative ratio of annual recharge‐precipitation varied from 43% to 69%. From a monthly recharge perspective, the majority (80%) of recharge due to precipitation occurred during the hydrologic winter period. The comparison of the recharge estimates with other studies indicates a good agreement. Furthermore, this method is able to predict transient recharge estimates, and can provide a reasonable tool for estimates on nutrient leaching that is often controlled by strong precipitation events and rapid infiltration of water and nitrate into the soil.     

Comparison of Recharge Estimation Methods During a Wet Period in a Karst Aquifer

Management of water resources, implying their appropriate protection, calls for a sound evaluation of recharge. Such assessment is very complex in karst aquifers. Most methods are developed for application to detrital aquifers, without taking into account the extraordinary heterogeneity of porosity and permeability of karst systems. It is commonly recommended to estimate recharge using multiple methods; however, differences inherent to the diverse methods make it difficult to clarify the accuracy of each result. In this study, recharge was estimated in a karst aquifer working in a natural regime, in a Mediterranean‐type climate, in the western part of the Sierra de las Nieves (southern Spain). Mediterranean climate regions are characterized by high inter‐annual rainfall variability featuring long dry periods and short intense wet periods, the latter constituting the most important contribution to aquifer water input. This paper aims to identify the methods that provide the most plausible range of recharge rate during wet periods. Six methods were tested: the classical method of Thornthwaite‐Mather, the Visual Balan code, the chloride balance method, and spatially distributed methods such as APLIS, a novel spatiotemporal estimation of recharge, and ZOODRM. The results help determine valid methods for application in the rest of the unit of study and in similar karst aquifers.     

Joint Estimation of Gross Recharge,Groundwater Usage,and Hydraulic Properties within HydroSight

Groundwater management decisions are often founded upon estimates of aquifer hydraulic properties, recharge and the rate of groundwater usage. Too often hydraulic properties are unavailable, recharge estimates are very uncertain, and usage is unmetered or infrequently metered over only recent years or estimated using numerical groundwater models decoupled from the drivers of drawdown. This paper extends the HydroSight groundwater time-series package ( http://peterson-tim-j.github.io/HydroSight/ ) to allow the joint estimation of gross recharge, transmissivity, storativity, and daily usage at multiple production bores. A genetic evolutionary scheme was extended from estimating time-series model parameters to also estimating time series of usage that honor metered volumes at each production bore and produces (1) the best fit with the observed hydrograph and (2) plausible estimates of actual evapotranspiration and hence recharge. The reliability of the approach was rigorously tested. Repeated calibration of models for four bores produced estimates of transmissivity, storativity, and mean recharge that varied by a factor of 0.22-0.32, 0.13-0.2, and 0.03-0.48, respectively, when recharge boundary effects were low and the error in monthly, quarterly, and biannual metered usage was generally <10%. Application to the 30 observation bores within the Warrion groundwater management area (Australia), produced a coefficient of efficiency of ≥0.80 at 22 bores and ≥0.90 at 12 bores. The aquifer transmissivity and storativity were reasonably estimated, and were consistent with independent estimates, while mean gross recharge may be slightly overestimated. Overall, the approach allows greater insights from the available data and provides opportunity for the exploration of usage and climatic scenarios.     

Estimation of Apollo Lunar Dust Transport using Optical Extinction Measurements

A technique to estimate mass erosion rate of surface soil during landing of the Apollo Lunar Module (LM) and total mass ejected due to the rocket plume interaction is proposed and tested. The erosion rate is proportional to the product of the second moment of the lofted particle size distribution N(D), and third moment of the normalized soil size distribution S(D), divided by the integral of S(D)?D2/v(D), where D is particle diameter and v(D) is the vertical component of particle velocity. The second moment of N(D) is estimated by optical extinction analysis of the Apollo cockpit video. Because of the similarity between mass erosion rate of soil as measured by optical extinction and rainfall rate as measured by radar reflectivity, traditional NWS radar/rainfall correlation methodology can be applied to the lunar soil case where various S(D) models are assumed corresponding to specific lunar sites.     

Recharge characteristics of an unconfined aquifer from the rainfall-water table relationship

The determination of recharge levels of unconfined aquifers, recharged entirely by rainfall, is done by developing a model for the aquifer that estimates the water-table levels from the history of rainfall observations and past water-table levels. In the present analysis, the model parameters that influence the recharge were not only assumed to be time dependent but also to have varying dependence rates for various parameters. Such a model is solved by the use of a recursive least-squares method. The variable-rate parameter variation is incorporated using a random walk model. From the field tests conducted at Tomago Sandbeds, Newcastle, Australia, it was observed that the assumption of variable rates of time dependency of recharge parameters produced better estimates of water-table levels compared to that with constant-recharge parameters. It was observed that considerable recharge due to rainfall occurred on the very same day of rainfall. The increase in water-table level was insignificant for subsequent days of rainfall. The level of recharge very much depends upon the intensity and history of rainfall. Isolated rainfalls, even of the order of 25 mm day⁻¹, had no significant effect on the water-table levels.     

Recharge of aquifers by flood events in an arid region

The process of aquifer recharge by flood events in an arid region was investigated as applied to the Hazeva Formation (the Karkom graben, the Wadi Paran watershed, Israel). The hydrological model was established as a complex system, with due regard for groundwater and transmission losses of surface runoff. It was based on a previously outlined hydrogeological model of the Karkom graben and a model of transmission losses in arid watercourses under conditions of data deficiency. Proceeding from calculation of groundwater balances, the contribution of surface runoff as a decisive balance component was confirmed. The main characteristics of aquifer regimes, such as changes in storage volume and groundwater level, as well as lateral flow, were all found to be dependent upon the net extraction rate, i.e. pumpage discounting replenishment by flood events. Analysis and physical interpretation of model parameters enabled assessment of the influence of groundwater extraction on aquifer recharge. This became apparent as increasing absorption capacity and recharge availability of the aquifer as a result of the groundwater abstraction. Copyright © 2002 John Wiley & Sons, Ltd.     

接收函数的泊松比测量方法及大陆地壳构成的判断

地震观测是了解地球内部物理状态的直接手段,通过一些弹性参数可以推测地球内部的物质构成,而相应的物质构成对分析大陆地壳演化的过程具有重要意义。泊松比是推测地球内部物质构成的有效参数之一,接收函数方法分离出的Ps转换波为获取泊松比提供了一条行之有效的便捷途径。     

Interpolation of Steady-State Concentration Data by Inverse Modeling

In most groundwater applications, measurements of concentration are limited in number and sparsely distributed within the domain of interest. Therefore, interpolation techniques are needed to obtain most likely values of concentration at locations where no measurements are available. For further processing, for example, in environmental risk analysis, interpolated values should be given with uncertainty bounds, so that a geostatistical framework is preferable. Linear interpolation of steady-state concentration measurements is problematic because the dependence of concentration on the primary uncertain material property, the hydraulic conductivity field, is highly nonlinear, suggesting that the statistical interrelationship between concentration values at different points is also nonlinear. We suggest interpolating steady-state concentration measurements by conditioning an ensemble of the underlying log-conductivity field on the available hydrological data in a conditional Monte Carlo approach. Flow and transport simulations for each conditional conductivity field must meet the measurements within their given uncertainty. The ensemble of transport simulations based on the conditional log-conductivity fields yields conditional statistical distributions of concentration at points between observation points. This method implicitly meets physical bounds of concentration values and non-Gaussianity of their statistical distributions and obeys the nonlinearity of the underlying processes. We validate our method by artificial test cases and compare the results to kriging estimates assuming different conditional statistical distributions of concentration. Assuming a beta distribution in kriging leads to estimates of concentration with zero probability of concentrations below zero or above the maximal possible value; however, the concentrations are not forced to meet the advection-dispersion equation.     

跨断层形变测量异常特征分析

在统计近40年我国强震前跨断层形变异常的基础上, 对异常持续时间、 异常空间分布、 异常幅度特征及它们之间的关系进行了分析, 讨论了跨断层形变观测异常特征和监测不同震级地震跨断层场地的最大间距及观测周期。 结果表明: 异常主要以中短期和中期异常为主, 尤其在震前1年内异常最多; 异常持续时间与震级呈正比例的关系; 异常在空间分布上有随震级增大而扩大的现象; 异常幅度有随异常持续时间增大而增大的趋势; 震中距在160~350 km范围内异常幅度较大; 异常形态主要分为趋势型和突变型两种。 监测不同震级的地震跨断层形变场地间距可以不同, 监测7级地震形变场地间距应小于450 km; 6级应小于300 km; 5级应小于200 km; 4级应小于100 km。 跨断层形变观测周期应不大于3个月。