Alluviums are geological units of fundamental importance for water supply in semi-arid regions of northeastern Brazil. Characterizing alluvial aquifers becomes a key action in the sustainable management of already scarce water resources in the region. Generally, to quantify the storage capacity of these sites and aquifers recharge the hypothesizes that the soil is homogeneous at the field scale or at the mesoscale are adopted. This context neglects the impacts that a heterogeneous profile can cause in the vadose zone flows processes. It can lead to estimation errors putting at risk those water resources so important for the diffuse population. This paper presents a hydrodynamic modeling of the unsaturated zone with a heterogeneous profile in a soil alluvial in the Capibaribe River Basin - Pernambuco - Brazil. Threedimensional infiltration tests were carried out, using single ring infiltrometers of 8.2 cm diameter at different depths of the soil and 100 cm in diameter to evaluate the influence of heterogeneity on the water flow in the field scale. The collected data were used to determine the hydrodynamic properties of the soil with the aid of the Beerkan method with the BEST algorithm. The soil profile was represented by the mapping performed with the ground penetration radar (GPR) and later built in the Hydrus model, considering a heterogeneous and bidimensional simulation profile. The following scenarios were adopted for the modeling: events of internal drainage, variable flow and infiltration tests. An equivalent profile model was proposed to study the phenomenon of soil water transfer in a simpler way, providing a representative equivalent curve for the profile. This model had a good adjustment, generating water transference predictions close to the real. However, it cannot be used to evaluate the behavior of preferential flows of the soil, since it does not quantify sectors, but rather the entire profile. It was observed that, in a heterogeneous soil profile, hydraulic barriers could be created due to pore connectivity factors and distinct water retention between the layers and, consequently, to generate suspended groundwater. Finally, an empirical model of deep drainage flow was proposed, based on hydrodynamic soil data to quantify possible volumes of water drained by a flow or constant pressure event at the soil surface.
ALLENDE - PIEDRAS NEGRAS TRANSBOUNDARY AQUIFER: AN INITIAL MODELING ASSESSMENT
Recently, a total of 36 potential transboundary aquifers have been identified in the Mexican-U.S border. Sixteen aquifers were identified and characterized as transboundary with enough level of confidence; however, only 11 aquifers have been recognized officially as transboundary by Mexico and the United States. The Allende-Piedras Negras aquifer between Texas and the state of Coahuila, Mexico, has been identified as transboundary with reasonable level of confidence; however, it has not been recognized officially by both countries or at international level (ISARM). The purpose of this work is to demonstrate the hydrogeological linkages of this aquifer at transboundary level as well to offer a better understanding of the system with the objective to offer new information that could support its identification and recognition at international levels.
In order to accomplish this objective, a simulation tool will be developed and tested using available well data from prevous studies in the region using primarily historical piezometric levels. The capacities of a modeling tool (MODFLOW) will be tested to verify the hydraulic connectivity of the transboundary aquifer system. After confirmimg the connection of the transboundary flow, and due to limited water well data in the Mexican side, extraction scenarios will be tested to offer potential consequences of the system in both sides of the border, if excessive water extraction occurs. Some of the hydraulic properties will be taken from hydrological studies and previous pumping tests if availabe to start the modeling process; if there is missing informaion, it would be taken from calibration or available data from closer areas, such as hydrulic conductivity or permeability values.
The methodology followed to perform this project will also include the collection of geological information to homogenize and correlate the geological units in both sides of the border. This process would provide more refined information of the aquifers already identified and laking of information. The expected results will offer both the grounds for future simulation models in the poorly studied aquifers in the border between Texas and Coahuila and provide the first assessments for potential groundwater management in the region.
Whole Japanese Archipelago is in serious peril of severe earthquakes as witnessed in the past, because it is situated in the Circum-Pacific Seismic Zone, one of the major seismic zones caused by the plate tectonics. Many Southeast Asian countries as well as North and South American countries facing the Pacific Ocean are also located in the same seismic zone. Most of the megacities not only in Japan but Southeast Asian countries are located on the alluvial plains where the ground is very soft and especially vulnerable for groundwater related disasters like landslides and liquefactions.
Since groundwater is a crucial water resource for most of the cities around the world, it is very important as the first step to understand and evaluate the impact of a huge earthquake on the groundwater levels not only for developing disaster risk deduction countermeasures for land subsidence and liquefaction, but also waster resource risk management. However, so far, almost no such studies have been carried out mainly because no densely distributed groundwater level observations were available at a short time interval when a large earthquake occurred.
The Great East Japan Earthquake occurred at 14:46 JST on March 11, 2011, which was the strongest earthquake on record in Japan (the 4th biggest in the world) with a magnitude of 9.0 (Mw). More than 18,000 people were sacrificed or missing by the earthquake mostly by Tsunami generated by it. In Tokyo Metropolis, the hourly groundwater levels have been observed at 42 sites sine 1952 in order to mainly monitor the land subsidence situation. When the Great East Japan Earthquake occurred, large fluctuations of confined and unconfined groundwater levels were observed at 102 observation wells in Tokyo, although Tokyo is located around 400 km far away from the epicenter.
Under the above background, in this study, taking full advantage of the unique rare case data from the dense groundwater monitoring network in Tokyo, we investigate the fluctuation patterns of confined and unconfined groundwater levels caused by the Great East Japan Earthquake. The groundwater level data used in this study consist of one month time series in March 2011 with one-hour interval.
The fluctuation patterns of groundwater levels caused by the earthquake were identified using Self-Organizing Maps (SOM). The SOM can project high-dimensional, complex target data onto a two-dimensional regularly arranged map in proportion to the degree of properties. As for the results, the fluctuation patterns of the groundwater level were classified into eight clusters. Either abrupt rise or sharp drawdown pattern was identified right after the earthquake for most of the wells. Abrupt rise pattern was typical for the unconfined groundwater levels. For the confined groundwater levels, sharp drawdown just after the earthquake occurred about 90% of the wells, which is inferred as the result of the pressure release derived from crustal expansion. Groundwater level rising just after the earthquake especially for unconfined groundwater may be caused by the phenomenon of liquefaction. In addition, the spatial characteristics of these patterns were also investigated in this study.