The water resources that supply most of the megacities in the world are under increased pressure because of land transformation, population growth, rapid urbanization, and climate-change impacts. Dhaka, in Bangladesh, is one of the largest of 22 growing megacities in the world, and it depends on mainly groundwater for all kinds of water needs. The regional groundwater-flow model MODFLOW-2005 was used to simulate the interaction between aquifers and rivers in steady-state and transient conditions during the period 1981–2013, to assess the impact of development and climate change on the regional groundwater resources. Detailed hydro-stratigraphic units are described according to 150 lithology logs, and a three-dimensional model of the upper 400 m of the Greater Dhaka area was constructed. The results explain how the total abstraction (2.9 million m3/d) in the Dhaka megacity, which has caused regional cones of depression, is balanced by recharge and induced river leakage. The simulated outcome shows the general trend of groundwater flow in the sedimentary Holocene aquifers under a variety of hydrogeological conditions, which will assist in the future development of a rational and sustainable management approach.
International Journal of Earth Sciences - The El Abra porphyry copper deposit belongs to the Late Eocene—Early Oligocene metallogenic belt of northern Chile, which host several world-class... 相似文献
The US Army Corps of Engineers (USACE) and the South Florida Water Management District (SFWMD) are partners in an ambitious plan to restore water flows throughout the Everglades ecosystem. An important component of the restoration plan involves storing excess stormwater deep underground in the Floridan Aquifer System using aquifer, storage and recovery (ASR) wells. In order to determine the optimal ASR system and to assess environmental impacts, USACE spent over 11 years and significant resources to develop a three-dimensional groundwater model of the Floridan Aquifer System covering a large portion of the Florida peninsula. This SEAWAT model is capable of evaluating changes in aquifer pressures and density-dependent flows in the entire study area. The model has been used to evaluate the Everglades ASR system already but could also be used by water managers for other important water resources studies in Florida including water supply estimates and adaptation to climate change. As part of an effort to make the model more readily available for other important studies, this study documents and summarizes the overall development of the SEAWAT model including a discussion regarding the intensive calibration and validation efforts undertaken during model development. The paper then demonstrates the use of the model using Everglades ASR project alternatives. Lastly, the paper outlines potential future uses of the model along with its overall limitations. Supplementary online resources are also included that provide researchers with further detail regarding the model development effort beyond the scope of this summary article as well as model development databases. 相似文献
While restoring hyporheic flowpaths has been cited as a benefit to stream restoration structures, little documentation exists confirming that constructed restoration structures induce comparable hyporheic exchange to natural stream features. This study compares a stream restoration structure (cross‐vane) to a natural feature (riffle) concurrently in the same stream reach using time‐lapsed electrical resistivity (ER) tomography. Using this hydrogeophysical approach, we were able to quantify hyporheic extent and transport beneath the cross‐vane structure and the riffle. We interpret from the geophysical data that the cross‐vane and the natural riffle induced spatially and temporally unique hyporheic extent and transport, and the cross‐vane created both spatially larger and temporally longer hyporheic flowpaths than the natural riffle. Tracer from the 4.67‐h injection was detected along flowpaths for 4.6 h at the cross‐vane and 4.2 h at the riffle. The spatial extent of the hyporheic zone at the cross‐vane was 12% larger than that at the riffle. We compare ER results of this study to vertical fluxes calculated from temperature profiles and conclude significant differences in the interpretation of hyporheic transport from these different field techniques. Results of this study demonstrate a high degree of heterogeneity in transport metrics at both the cross‐vane and the riffle and differences between the hyporheic flowpath networks at the two different features. Our results suggest that restoration structures may be capable of creating sufficient exchange flux and timescales of transport to achieve the same ecological functions as natural features, but engineering of the physical and biogeochemical environment may be necessary to realize these benefits. 相似文献
We investigate the importance of selecting two different methodologies for the determination of hydraulic conductivity from
available grain-size distributions on the stochastic modeling of the depth-averaged breakthrough curve observed during a forced-gradient
tracer test experiment. The latter was performed in the Lauswiesen alluvial aquifer, located near the city of Tübingen, Germany,
by injecting NaBr into a well at a distance of about 50 m from a pumping well. We also examine the joint effect of the choice
of the transport model adopted to describe solute transport at the site and the way the spatial distribution of porosity is
assessed. In the absence of direct measurements of porosity, we consider: (a) the model used by Riva et al. (J Contam Hydrol
88:92–118, 2006; J Contam Hydrol 101:1–13, 2008), which relates the natural logarithms of effective porosity and conductivity through an empirical, experimentally-based,
linear relationship derived for a nearby experimental site; and (b) a model based on a commonly used relationship linking
the total porosity to the coefficient of uniformity of grain size distributions. Transport is described in terms of a purely
advective process and/or by including mass exchange processes between mobile and immobile regions. Modeling of flow and transport
is performed within a Monte Carlo framework, upon conceptualizing the aquifer as a random composite medium. Our results indicate
that the model adopted to describe the correlation between conductivity and porosity and the way grain-sieve information are
incorporated to depict the heterogeneous distribution of hydraulic conductivity can have relevant effects in the interpretation
of the data at the site. All the conceptual models employed to describe the structural heterogeneity of the system and transport
features can reasonably reproduce the global characteristics of the experimental depth-averaged breakthrough curve. Specific
details, such as the peak concentration and the time of first arrival, can be better reproduced by a double porosity transport
model when a correlation between conductivity and porosity based on grain size information at the site is considered. The
best prediction of the late-time behavior of the measured breakthrough curves, in terms of the observed heavy tailing, is
offered by directly linking porosity distribution to the spatial variability of particle size information. 相似文献
In this paper, we discuss observations of temperature variability in the tidal portion of the San Joaquin River in California.
The San Joaquin River makes up the southern portion of the Sacramento San Joaquin Delta, the eastern end of San Francisco
Bay. Observations made in August 2004 and August 2005 show significant diurnal variations in temperature in response to surface
heat exchange. However, to account for observed changes in heat content a sizeable downstream heat flux (approximately 100 W
m−2) must be added to the surface heat flux. To account for this flux via Fickian dispersion, a flow-dependent dispersion coefficient
varying from 500 to 4,000 m2 s−1 is needed. These values are much larger than would be predicted for a river of this size, suggesting that the complex topology
of the Delta greatly enhances longitudinal dispersion. Building on these observations, we present a simple theory that explores
how the subtidal temperature field varies in response to changes in flow rate, dispersion, and heat exchange. 相似文献