Simulation of groundwater flow in a crystalline rock aquifer system in Southern Ghana – An evaluation of the effects of increased groundwater abstraction on the aquifers using a transient groundwater flow model          下载免费PDF全文

Sandow Mark Yidana  Bob Alfa  Bruce Banoeng‐Yakubo  Millicent Obeng Addai 《水文研究》2014,28(3):1084-1094

Monitored groundwater level data, well logs, and aquifer data as well as the relevant surface hydrological data were used to conceptualise the hydrogeological system of the Densu Basin in Southern Ghana. The objective was to numerically derive the hydraulic conductivity field for better characterization of the aquifer system and for simulating the effects of increasing groundwater abstraction on the aquifer system in the basin. The hydraulic conductivity field has been generated in this study through model calibration. This study finds that hydraulic conductivity ranges between a low of 2 m/d in the middle sections of the basin and about 40 m/d in the south. Clear differences in the underlying geology have been indicated in the distribution of aquifer hydraulic conductivities. This is in consonance with the general assertion that the hydrogeological properties of the aquifers in the crystalline basement terrains are controlled by the degree of fracturing and/or weathering of the country rock. The transient model suggest aquifer specific storage values to range between 6.0 × 10^?5 m^?1 and 2.1 × 10^?4 m^?1 which are within acceptable range of values normally quoted for similar lithologies in the literature. There is an apparent subtle decrease in groundwater recharge from about 13% of the annual precipitation in 2005 to about 10.3% of the precipitation in 2008. The transient model was used to simulate responses of the system to annual increment of groundwater abstraction by 20% at the 2008 recharge rates for the period 2009 – 2024. The results suggest that the system will not be able to sustain this level of abstraction as it would lead to a basin wide drawdown in the hydraulic head by 4 m by the end of the prediction period. It further suggests a safe annual increment in groundwater abstraction by 5% under business as usual recharge conditions. Identification and protection of groundwater recharge areas in the basin are recommended in order to safeguard the integrity of the resource under the scenario of increased abstraction for commercial activities in the basin. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Regime theories in gravel‐bed rivers: models,controlling variables,and applications in disturbed Italian rivers          下载免费PDF全文

G. Kaless  L. Mao  M. A. Lenzi 《水文研究》2014,28(4):2348-2360

Downstream hydraulic geometry relationships describe the shape of alluvial channels in terms of bankfull width, flow depth, flow velocity, and channel slope. Recent investigations have stressed the difference in spatial scales associated with these variables and thus the time span required for their adjustment after a disturbance. The aim of this study is to explore the consequences in regime models considering the hypothesis that while channel width and depth adjust quickly to changes in water and sediment supply, reach slope requires a longer time span. Three theoretical models were applied. One model incorporates an extremal hypothesis (Millar RG. 2005. Theoretical regime equations for mobile gravel‐bed rivers with stable banks. Geomorphology 64 : 207–220), and the other two are fully physically based (Ikeda S, Parker G, Kimura Y. 1988. Stable width and depth of straight gravel rivers with heterogeneous bed materials. Water Resources Research 24 : 713–722; Parker G, Wilcock PR, Paola C, Dietrich W, Pitlick J. 2007. Physical basis for quasi universal relations describing bankfull hydraulic geometry of single‐thread gravel‐bed rivers. Journal of Geophysical Research 112 , DOI: 10.1029/2006JF000549). In order to evaluate the performance of models introducing the slope as an independent variable, we propose two modifications to previous models. The performance of regime models was tested against published data from 142 river reaches and new hydraulic geometry data from gravel‐bed rivers in Patagonia (Argentina) and north‐eastern Italy. Models that assume slope as a control (Ikeda et al., 1988; or Millar, 2005) predict channel depth and width reasonably well. Parker et al.'s (2007) model improved predictions because it filters the scatter in slope data with a relation slope–discharge. The extremal hypothesis model of Millar (2005) predicts comparably to the other physically based models. Millar's model was chosen to describe the recent changes in the Piave and Brenta rivers due to human intervention – mainly in‐channel gravel mining. The change in sediment supply and recovery was estimated for these rivers. This study supports the interpretation that sediment supply is the key factor guiding morphological changes in these rivers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Estimating field‐saturated soil hydraulic conductivity by a simplified Beerkan infiltration experiment          下载免费PDF全文

V. Bagarello  S. Di Prima  M. Iovino  G. Provenzano 《水文研究》2014,28(3):1095-1103

Field‐saturated soil hydraulic conductivity, K_fs, is highly variable. Therefore, interpreting and simulating hydrological processes, such as rainfall excess generation, need a large number of K_fs data even at the plot scale. Simple and reasonably rapid experiments should be carried out in the field. In this investigation, a simple infiltration experiment with a ring inserted shortly into the soil and the estimation of the so‐called α* parameter allowed to obtain an approximate measurement of K_fs. The theoretical approach was tested with reference to 149 sampling points established on Burundian soils. The estimated K_fs with the value of first approximation of α* for most agricultural field soils (α* = 0.012 mm^?1) differed by a practically negligible maximum factor of two from the saturated conductivity obtained by the complete Beerkan Estimation of Soil Transfer parameters (BEST) procedure for soil hydraulic characterization. The measured infiltration curve contained the necessary information to obtain a site‐specific prediction of α*. The empirically derived α* relationship gave similar results for K_fs (mean = 0.085 mm s^?1; coefficient of variation (CV) = 71%) to those obtained with BEST (mean = 0.086 mm s^?1; CV = 67%), and it was also successfully tested with reference to a few Sicilian sampling points, since it yielded a mean and a CV of K_fs (0.0094 mm s^?1 and 102%, respectively) close to the values obtained with BEST (mean = 0.0092 mm s^?1; CV = 113%). The developed method appears attractive due to the extreme simplicity of the experiment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Estimation of soil hydraulic properties and their uncertainty through the Beerkan infiltration experiment          下载免费PDF全文

Saeed Ghavidelfar  Asaad Y. Shamseldin  Bruce W. Melville 《水文研究》2015,29(17):3699-3713

The Beerkan method based on in situ single‐ring water infiltration experiments along with the relevant specific Beerkan estimation of soil transfer parameters (BEST) algorithm is attractive for simple soil hydraulic characterization. However, the BEST algorithm may lead to erroneous or null values for the saturated hydraulic conductivity and sorptivity especially when there are only few infiltration data points under the transient flow state, either for sandy soil or soils in wet conditions. This study developed an alternative algorithm for analysis of the Beerkan infiltration experiment referred to as BEST‐generalized likelihood uncertainty estimation (GLUE). The proposed method estimates the scale parameters of van Genuchten water retention and Brooks–Corey hydraulic conductivity functions through the GLUE methodology. The GLUE method is a Bayesian Monte Carlo parameter estimation technique that makes use of a likelihood function to measure the goodness‐of‐fit between modelled and observed data. The results showed that using a combination of three different likelihood measurements based on observed transient flow, steady‐state flow and experimental steady‐state infiltration rate made the BEST‐GLUE procedure capable of performing an efficient inverse analysis of Beerkan infiltration experiments. Therefore, it is more applicable for a wider range of soils with contrasting texture, structure, and initial and saturated water content. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Steady state flow with hydraulic conductivity change around large diameter wells     

A. Altunkaynak  Z. Şen 《水文研究》2011,25(11):1778-1783

Darcian flow law in aquifers assumes that the aquifer hydraulic conductivity is constant and the groundwater movement is due only to the piezometric level changes through hydraulic gradient. In practice, after the well development the aquifer just around the well has comparatively larger hydraulic conductivity and gradient. Patchy aquifer solutions in the literature consider sudden hydraulic conductivity changes with distance for the steady state flow. The change of transmissivity is demonstrated by the application of slope‐matching procedure to actual field data. It is the main purpose of this paper to derive simple analytical expressions for aquifer parameter evaluations with steadily decreasing hydraulic conductivity around the well. Spatial nonlinear hydraulic conductivity changes around a large‐diameter well within the depression cone of a confined aquifer are considered as exponentially decreasing functions of the radial distance. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A coupled analysis of cavity and pore volume changes for pulse tests conducted in soft clay deposits     

François Duhaime  Robert P. Chapuis 《国际地质力学数值与分析法杂志》2014,38(9):903-924

This paper presents a new interpretation method for pulse tests, a field permeability test that allows for rapid measurements of hydraulic conductivity k in aquitards. This new method applies to soft clay deposits. To initiate a pulse test, a known volume of water is injected into the sand filter of a monitoring well isolated by a packer. The resulting pressure increase yields an outward movement of the sand filter cavity wall. After presenting the usual interpretation methods and their limits, this paper proposes a new interpretation method based on a coupled analysis of the pressure and displacement fields in the soil using the Biot–Darcy formulation. A series of analytical and numerical non‐dimensional velocity graphs, normalized plots of the mean hydraulic head difference versus its rate of change, are given. For a linear elastic material, these type curves show relatively small variations with the sand filter aspect ratio and the Poisson ratio of the tested clay. The type curves are also found to be independent of the clay compressibility (m_v) and k, an important result. A series of pulse tests conducted in a soft marine clay deposit near Montreal, Canada, are interpreted with the proposed method. The hydraulic conductivity values calculated from these tests are closely correlated with independent estimates obtained using long‐duration variable‐head tests. Compared with previous interpretation methods, the proposed method allows soil volume changes to be reconciled with cavity expansion phenomena and the range of type curves available for the interpretation of test data to be constrained. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Fire decreases near‐surface hydraulic conductivity and macropore flow in blanket peat          下载免费PDF全文

Joseph Holden  Catherine Wearing  Sheila Palmer  Benjamin Jackson  Kerrylyn Johnston  Lee E. Brown 《水文研究》2014,28(5):2868-2876

Many peatlands have been subjected to wildfire or prescribed burning, but it is not known how these fires influence near‐surface hydrological processes. Macropores are important flowpaths in the upper layers of blanket peat and were investigated through the use of tension disc infiltrometers, which also provide data on saturated hydraulic conductivity. Measurements were performed on unburnt peat (U), where prescribed burning had taken place 2 years (B2), 4 years (B4) and >15 (B15+) years prior to sampling, and where a wildfire (W) had taken place 4 months prior to sampling. Where there had been recent burning (B2, B4 and W), saturated hydraulic conductivity was approximately three times lower than where there was no burning (U) or where burning was last conducted >15 years ago (B15+). Similarly, the contribution of macropore flow to overall infiltration was significantly lower (between 12% and 25% less) in the recently burnt treatments compared to B15+ and U. There were no significant differences in saturated hydraulic conductivity or macropore flow between peat that had been subject to recent wildfire (W) and those that had undergone recent prescribed burning (B2 and B4). The results suggest that fire influences the near‐surface hydrological functioning of peatlands but that recovery in terms of saturated hydraulic conductivity and macropore flow may be possible within two decades if there are no further fires. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Flood‐loss modelling for assessing impacts of flood‐frequency adjustment,Middle Mississippi River,USA     

Nicholas Pinter  Jennifer Dierauer  Jonathan W. F. Remo 《水文研究》2012,26(19):2997-3002

This study modelled flood losses (economic damages) along the Middle Mississippi River (MMR) (1) using current US government estimates of flow frequencies and (2) using frequencies based on the original, unaltered discharge measurements. The official flood frequencies were quantified in the Upper Mississippi River System Flow Frequency Study (UMRSFFS), but as a last step in that study, early discharges along the MMR were reduced by up to 54% to reflect a purported bias in early measurements. Subsequently, early discharge measurements were rigorously tested, and no such bias was found. Here, flood damages were quantified using a combination of one‐dimensional hydraulic modelling and flood‐loss modelling. For all recurrence intervals, damages were much less using the UMRSFFS flow frequencies compared with the frequencies based on the original discharge measurements, with differences ranging up to 79% (100‐year event) and $2.9bn (200‐year event). Annualized losses in the study area based on the UMRSFFS frequencies were just $41.6m versus $125.6m using the raw frequencies (an underestimation of 67%). These totals do not include flood losses elsewhere along the MMR, including in metropolitan St Louis. In summary, a seemingly small methodological adjustment – in this case, a single hidden adjustment, not documented anywhere within the UMRSFFS – can have dramatic societal impacts in terms of underestimation of flood probabilities and flood risk. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Physical-hydraulic properties of tropical sandy-loam soil in response to rice-husk dust and cattle dung amendments and surface mulching     

Gloria I. Ezenne  Jane Tanner 《水文科学杂志》2013,58(14):1746-1754

ABSTRACT

The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface mulching with dry grasses/legume, on the infiltration characteristics and intrinsic structural properties of a deep, well-drained soil in southeastern Nigeria are assessed. Treatments are RHD-amended, CD-amended and “unamended”, each plot being either surface-mulched or left bare, with the unamended-bare plots as control. Amendments and mulch were applied at 20 t/ha equivalents. Their effects on the soil’s infiltration characteristics 7 months later were not evident; however, there was a tendency for differences: CD-amended ≥ RHD-amended ≥ unamended and surface-mulched ≥ bare-surface. By contrast, saturated hydraulic conductivity (K_s ) differed thus: CD-mulched ≥ unamended-mulched > the rest. Similar values were recorded for K_s (50.89 cm/h) and final infiltration rate (50.74 cm/h) only under CD-amended plots, which also showed the highest values (43.50 cm/h) for transmissivity of the soil. Soil penetrometer resistance was lowest in CD-amended plots (113.44 kPa) and highest in unamended plots (166.78 kPa). Topsoil addition of cattle dung and surface mulching could increase infiltration, though marginally, and permeability of coarse-textured tropical soils beyond the season of their application when their effects on soil structure have almost waned.  相似文献   

Infiltration mechanisms in a herbaceous peat: results of a controlled infiltration experiment/Mécanismes d'infiltration dans une tourbière herbacée: résultats d'une expérience d'infiltration contrôlée     

《水文科学杂志》2013,58(4)

Abstract

The theoretical spatial distribution of hydraulic head during infiltration is used to interpret the results of infiltration experiments made in the field on a single, isolated, column of herbaceous peat in a flood-plain wetland in central England. Crusts of different hydraulic resistance were applied to the column surface. These regulated the water influx enabling the hydraulic conductivity of the peat to be estimated at between 1 and 19.5 m day^-1. It is inferred that, when the hydraulic gradient changes, water may follow different pathways through the peat. Water moves rapidly through macropores in proportion to the applied hydraulic gradient, and infiltrates the peat matrix from the macropore walls. The results indicate the significance of hydraulic conductivity variations with depth, and the importance of precipitation intensity.  相似文献