Groundwater Elevation Research Articles

Application of Fuzzy Logic in the Selection of a Suitable Sanitary Landfill Site for Solid Waste Disposal and Management in Coastal Area of Nigeria

Solid waste management has been identified as one of the most challenging environmental problems facing cities in most developing countries because of the risks to human health and the general environment. Different methods are available for solid waste disposal and they include; ocean dumping open burning and sanitary landfill. Of these available methods, sanitary landfill remains the most effective and hygienic method of solid waste disposal. Inspite of its effectiveness, the method of waste disposal using sanitary landfill is challenged by the availability of suitable land. To select a suitable site for landfill application numerous factors must be considered, ranging from; flood extent, stream, rivers, swampy areas, ground water, built-up areas, roads, slopes, airport, palaces and point of interests (POIs). In this study, fuzzy logic technique of data analysis was employed to analyze the various factors in order to select the most suitable site for landfill application in the study area. The basic steps involved in the application of fuzzy logic in the modeling and prediction of suitable site for landfill application are as follows; definition of input and output variables, conversion of crisp variables into fuzzy sets, definition of membership functions for each inputs and output variables, creation of fuzzy rules and simulation. Result of the fuzzy simulation revealed that; for river buffer distance of 0.9909km, ground water elevation of 7.13m, road buffer distance of 0.7727km, land slope of 2.673 0 and built-up area buffer distance of 1.37km, suitability ranking is 2 which mean “least suitable. For river buffer distance of 1.355km, ground water elevation of 9.537m, road buffer distance of 1.645km, land slope of 3.655 0 and built-up area buffer distance of 1.778km, suitability ranking is 3 which means “moderately suitable” and for river buffer distance of 2.5km, ground water elevation of 15m, road buffer distance of 2.5km, land slope of 6 0 and built-up area buffer distance of 2.5km, suitability ranking is 4 which means “highly suitable” Keywords: Sanitary landfill, Fuzzy logic, Membership functions, Fuzzy rules and Suitability rating DOI : 10.7176/JEES/10-1-07 Publication date: January 31 st 2020

Agricultural Practices and Hydrologic Conditions Shape the Temporal Pattern of Soil and Stream Water Dissolved Organic Matter

This study investigates the combined effects of land management and hydrology on the temporal dynamics of dissolved organic matter (DOM) quantity and composition in stream water and groundwaters in an agricultural watershed. We assessed dissolved organic carbon (DOC) concentrations, DOM UV–Vis absorbance, and DOM fluorescence in groundwater under cultivated upland, riparian grassland, and riparian woodland land covers, as well as in the stream water at the watershed outlet and livestock-impacted runoff. During one year, stream water and groundwater were monitored weekly to biweekly, complemented by sub-hourly stream sampling during seven storm events. Results showed that: (1) groundwater DOC concentration was lower in cultivated upland (6.4 ± 5.6 mg l−1) than in riparian grassland and woodland (22.4 ± 13.7 mg l−1 and 17.2 ± 9.9 mg l−1, respectively). (2) The proportion of microbially processed compounds decreased in the order upland cropland > riparian grassland > riparian woodland. (3) Principal component analysis (PCA) of groundwater DOM revealed a change in composition indicating that low-aromaticity microbially processed compounds were preferentially exported to the stream. (4) PCA of stream DOM indicated that seasonal increases in groundwater elevation expanded the contributing source areas, thereby increasing the connectivity between upland croplands and the stream, which amplified the effects of cultivation on fluvial DOM during the winter. (5) Storm events occurring after manure application in spring produced hot moments of manure-derived protein-like DOM transport to streams. Together, these results suggest that cultivated uplands in agricultural lands using animal manure as fertilizer may leach more DOM than vegetative buffers.

Evaluation of induced trench twin culverts constructed in deep fill

When culverts are installed beneath high embankments, earth loads become excessive and the induced trench construction method is a viable design option to reduce the culvert loads to acceptable levels. However, limited field studies evaluating the performance of induced trench twin culverts are reported in the literature and the practicality and effectiveness of the induced trench construction method (in general) has been subject to recent criticism. This paper describes the performance of twin 3048 mm inside-diameter reinforced concrete culverts constructed with an induced trench beneath 15.3 m of fill. Research instruments and autonomous data acquisition systems were installed during construction to monitor (i) culvert earth pressures, (ii) embankment deformations, and (iii) groundwater elevations in the vicinity of the compressible fill. The experimental observations recorded throughout the construction phase are presented herein; the embankment deformations are indicative of effective positive arching within the induced trench region, and the average earth pressure at the culvert crown was reduced to approximately 48% of the overburden soil pressure. The experimental data are compared with those reported in the literature by others, and the conclusions attained from this study demonstrate the effectiveness of the induced trench construction method.

Practical considerations for kriging groundwater surfaces

AbstractKriging is an accepted method of characterizing the groundwater elevation surface at sites where the water level data are available but where there may be insufficient additional data necessary for groundwater flow modeling. Groundwater surface interpolation via kriging is readily performed using commercial, state of the practice software, but some practitioners may not be able to justify such efforts because the process is not validated within studies documented in the peer‐reviewed literature. This paper describes the available kriging software and literature studies and then uses a case study to compare practical groundwater surface modeling to the studies available in the scientific literature. The literature review shows that the state of the practice as represented by the commercial software approach is consistent with the literature. Specifically, cokriging with groundwater elevation as the primary variable with trend removal and ground‐surface elevation as the secondary variable is an appropriate point of departure in practice. The literature review‐based summary of variogram model parameters (model type, nugget, sill, range, and trend model) was not useful as a quality‐control step to assess the reasonableness of variogram parameters identified by the standard practice of software‐assisted iteration when applied to the case‐study data set. The literature review indicated that groundwater elevation kriging has been performed using as few as 10 data points but a comparison of the case‐study simulated groundwater elevations and groundwater gradient magnitudes and directions indicated that the 30‐well threshold more commonly found in the literature was an appropriate minimum at the study site.

Sensitivity Analysis and Calibration of an Integrated Hydrologic Model in an Irrigated Agricultural Basin With a Groundwater‐Dependent Ecosystem

AbstractWhile sensitivity analysis and calibration are common practice in integrated hydrologic modeling, little work has been done to understand how the design of the sensitivity analysis and calibration affects the simulation outcome in these often highly nonlinear models. This is especially true for irrigated agricultural basins with a strong connection between land use, groundwater, and surface water. Using a range rather than a single set of initial parameter values, multiple sensitivity analyses, calibrations, and linearity tests were performed using UCODE_2014 on the Scott Valley Integrated Hydrologic Model. Calibration results show that parameters related to crop demand and applied irrigation water are most sensitive. Influence statistics show that low streamflow observations provide the most information during model calibration, indicating preference should be given to these observations during model development, sensitivity analysis, and calibration. Importantly, due to the nonlinearity of the integrated model, significant differences are found in results when initial parameter values are sampled from within their respective expected ranges. Estimates for some parameters varied up to an order of magnitude between calibrations, while all produced similar final objective function values, groundwater elevations, and stream flow. Confidence intervals for individual sensitivity analyses and calibration runs only spanned a fraction of the ensemble estimated parameter range across multiple runs. Our work suggests that a calibration design with multiple sensitivity analyses and calibrations of integrated hydrologic models, each using one of several widely varying sets of initial values, provides a frugal approach to identify parameters across the global parameter space.

Analyzing spatiotemporal characteristics of soil salinity in arid irrigated agro-ecosystems using integrated approaches

Soil salinization is one of the most common land degradation processes that impacts agricultural production, environmental health, and economic welfare. The first task in managing soil salinity is to understand its spatiotemporal characteristics, causal factors and influences, both over large regions and within individual fields. In this study, a typical irrigated agro-ecosystem located in the upper Yellow River basin, suffering from long-term soil salinization problems, was selected as the case study area. Field sampling experiments and investigations related to soil layer salt content, groundwater, irrigation and ground elevation were carried out at three scales (field scale, canal scale and regional scale) covering both croplands and natural vegetation patches during 2016 and 2017. Spatiotemporal characteristics of soil salinity were analyzed for the three scales based on sampling data, remote sensing, geostatistical analysis and model simulation. Results showed that, at the regional scale, the soil salinity distribution was dominated by topography and groundwater depth; at the canal scale, it was dominated by irrigation and cropping pattern; at the field scale, it was dominated by micro-topography and the uniformity of field irrigation. Scale-dependent soil salinity management strategies should be adopted to maintain agricultural production and the sustainability of natural ecosystems. It can be concluded that using integrated approaches including multi scale soil sampling, model simulation and other modern techniques is an effective way for thorough understanding and management of soil salinity.

Pengaruh Perbedaan Elevasi Muka Air Tanah Pada Pondasi Telapak Berdasarkan Studi Numerik

The south Kalimantan Province has various soil characteristic, the difference of ground water level included . Experimental modeling of foot plate foundations in various ground water level is too difficult to be performed. There were so many variables that need to be evaluated in the modeling. The numerical model was based on finite element method such in Abaqus allowed the modeling of foot plate foundations with the various of ground water level. This study modeled the foot plate foundation structure where located on various ground water level by giving variations of the effect of water level to the elevation of the foundation. Water level variations are determined successively below the foundation elevation, the same as the foundation elevation and above the foundation elevation. The analysis performed is static structure analysis with idealization of 2D shell idealization. The result of the research showed that the ground water level effect the stress and deformation of soil closed to foundation elevation. The stress had been evaluated at the base of the foundation for each ground water level difference correspondently 16,53 MPa, 9.34 MPa and 3.59 MPa. The lowest stresses was occured in ground water elevation above the foundation elevation (78.28%).

Evidence for Microbial Mediated NO3− Cycling Within Floodplain Sediments During Groundwater Fluctuations

The capillary fringe is a subsurface terrestrial-aquatic interface that can be a significant hotspot for biogeochemical cycling of terrestrially derived organic matter and nutrients. However, pathways of nitrogen (N) cycling within this environment are poorly understood, and observations of temporal fluctuations in nitrate (NO3 􀀀) concentrations lack the necessary resolution to partition between biotic or abiotic mechanisms. At discrete sampling points we measured NO3 􀀀, nitrite (NO2 􀀀), ammonium (NH4 +), gaseous nitrous oxide (N2O) and nitrogen (N2), and the corresponding isotopic composition of NO3 􀀀 within floodplain sediments at Rifle, Colorado. Coincident with an annually reoccurring spring/ summer excursion in groundwater elevation driven by snowmelt, we observed a rapid decline in NO3 􀀀 followed by transient peaks in NO2 􀀀, at three depths (2, 2.5 and 3 m) below the ground surface. Isotopic measurements (15N and 18O of NO3 􀀀) suggest an immediate onset of biological N loss at 2 m. At 2.5 and 3 m, NO3 􀀀 concentrations declined initially with no observable isotopic response, indicating dilution of NO3 􀀀 as the NO3 􀀀-deficient groundwater rose, followed by denitrification after prolonged saturation. A simple Rayleigh model further supports this depth-dependent variability in the significance of actively fractionating mechanisms (i.e., NO3 􀀀 reduction) relative to non-fractionating mechanisms (mixing and dilution). NO3 􀀀 reduction was calculated to be responsible for 64 % of the NO3 􀀀 decline at 2 m, 28 % at 2.5 and 47 % at 3 m, respectively. Finally, by accounting for previous molecular and geochemical analysis at this site, and comparing the trajectories between
15N:
18O, we conclude that biological NO3 􀀀 consumption at the two deeper and frequently saturated depths (2.5 and 3 m) can be attributed to heterotrophic denitrification. However, the
15N:
18O trajectory at the shallower, irregularly saturated site at 2 m shows a more complicated relationship best explained by the cyclic production of NO3 􀀀 via aerobic oxidation, and consumption via NO3 􀀀 reduction.

Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated‐Solvent Plume Site

AbstractGroundwater elevation fluctuation has been recognized as one mechanism causing temporal indoor air volatile organic chemical (VOC) impacts in vapor intrusion risk assessment guidance. For dissolved VOC sources, groundwater table fluctuation shortens/lengthens the transport pathway, and delivers dissolved contaminants to soils that are alternating between water saturated and variably saturated conditions, thereby enhancing volatilization potential. To date, this mechanism has not been assessed with field data, but enhanced VOC emission flux has been observed in lab‐scale and modeling studies. This work evaluates the impact of groundwater elevation changes on VOC emission flux from a dissolved VOC plume into a house, supplemented with modeling results for cyclic groundwater elevation changes. Indoor air concentrations, air exchange rates, and depth to groundwater (DTW) were collected at the study house during an 86‐d constant building underpressurization test. These data were used to calculate changes in trichloroethylene (TCE) emission flux to indoor air, during a period when DTW varied daily and seasonally from about 3.1 to 3.4 m below the building foundation (BF). Overall, TCE flux to indoor air varied by about 50% of the average, without any clear correlation to changes in DTW or its change rate. To complement the field study, TCE surface emission fluxes were simulated using a one‐dimensional model (HYDRUS 1D) for conditions similar to the field site. Simulation results showed time‐averaged surface TCE fluxes for cyclic water‐table elevations were greater than for stationary water‐table conditions at an equivalent time‐averaged water‐table position. The magnitudes of temporal TCE emission flux changes were generally less than 50% of the time‐averaged flux, consistent with the field site observations. Simulation results also suggested that TCE emission flux changes due to groundwater fluctuation are likely to be significant at sites with shallow groundwater (e.g., < 0.5 m BF) and permeable soil types (e.g., sand).

Drivers of peatland water table dynamics in the central Andes, Bolivia and Peru

AbstractCushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.

Exploring the potential for groundwater inundation in coastal US cities due to interactions between sewer infrastructure and global change

Urbanization, in particular, the culverting and burying of streams in sewer infrastructure, has affected both surface and subsurface flow regimes. While researchers have examined the impact of stream burial on groundwater budgets, field studies examining the influence of urbanization on groundwater dynamics are relatively scarce. This study analyzes tidal patterns in water-level data from shallow groundwater monitoring wells located next to a legacy sewer line within the city of Philadelphia, Pennsylvania, USA. The coupling of historic records, sewer network maps, and well bore hydrogeology explains spatial patterns in groundwater elevations. Furthermore, a synthesis of early twentieth century United States census data, and continental scale GIS data demonstrates the potential for groundwater inundation in coastal United States cities that are served by aging sewer infrastructure. Altered groundwater flow dynamics caused by sea level rise, coupled with climatic shifts will likely stress aging sewer infrastructure, and can lead to increased discharge of combined sewer overflow systems and flooding.

Identification of Source Water Mixing in the Fish Slough Spring Complex, Mono County, California, USA

While the desert ecosystem is highly dependent on the water resources that sustain it, the Fish Slough spring complex is an arid, spring-dependent wetland undergoing a multidecadal decline in spring outflow. This evaluation updates the source water forensics of the Fish Slough Spring complex, a substantial spring complex in the northern Owens Valley of the Basin and Range geomorphic provinces, in order to better understand the nature of the spring flow decline. The source of spring flow at Fish Slough was evaluated through an integration of the established geologic setting with measured groundwater elevations, and water quality and isotope chemistry compiled from both previously published sources and collection of new samples. While previous efforts to source the Fish Slough springs only considered potential source areas within the local geography, this evaluation considered a larger geographic extent for potential source areas to the spring water. The results infer that Fish Slough springs are sourced from multiple source water areas in hydraulic communication: a basin fill aquifer and warm, sodic spring systems with distinctive chemical signatures. Mixing from these sources occurs along two hypothesized flow paths, one from the northeast through the Tri-Valley area and one from the north and northwest through the Volcanic Tablelands. Northeast Spring has the strongest signature for Tri-Valley area waters, whereas the remaining Fish Slough Springs are comprised of a mixture of both flow paths. These conclusions have important implications for water management activities that have the potential to impact the desert ecosystem supported by these springs.

Environment-vulnerability evaluation of a high-speed railway line in Korea using a groundwater-anomaly method

The Republic of Korea completed the first phase of the Honam high-speed railway from Seoul to Gwangju in 2014, and the second phase from Gwangju to Mokpo will be completed in 2025. This study evaluates the vulnerability of the groundwater environment in the Cheonan-Iksan zone, which passes through three preliminary lines (the Cheonan-Daejeon-Iksan line, Cheonan-Gongju- Iksan line, and Cheonan-Osong-Iksan line) of the Honam high-speed railway, to determine the most suitable line. The groundwater-level anomaly is evaluated along the three lines of the high-speed railway. The depth to water ranged from 0.03 to 21.1 m and from 0.17 to 227.95 m (AMSL). To determine a suitable line for the high-speed railway, a groundwater-level anomaly (GLA) grade is used, which considers the spatial distributions of the depth to water and groundwater elevation. Based on the GLA evaluation index, the Cheonan-Daejeon-Iksan (CDI) line exhibited the highest vulnerability (85.39), while the Cheonan-Osong-Iksan (COI) line had the lowest vulnerability (47.41). Vulnerable geological engineering, which is indicated by a discharge-estimation (DE) grade higher than 4, occurred in a section of the CDI line with a DE grade of 9, suggesting that attention should be directed to the discharge of groundwater during tunnel excavation.

Saltwater Intrusion Zone Mapping on Shallow Groundwater Aquifer in Selat Baru, Bengkalis Island, Indonesia

Saltwater intrusion becomes a common problem in coastal area. Northern coast of Bengkalis Island in Riau, Indonesia that contiguously to Malacca Strait is experiencing the problem particularly in Selat Baru area which considered as developing area and most of the people live close to the sea. Dug well is the main source of groundwater that had been used by the population in Selat Baru and as the increasing of land occupation, the demand of clean water is rising up followed by the number of dug well. A study of groundwater monitoring was conducted to identify the zone of saltwater intrusion. Field observation had done by measuring the water level and physical parameters of groundwater such as taste, pH, electrical conductivity (EC) and total dissolved solid (TDS) from 110 existing dug wells. Some conus feature had found from groundwater elevation map which indicated lower water level caused by excessive groundwater pumping. Generally, pH shows values from 6-8 that was still in range of water quality standard, but there are 20 wells (18%) that have pH below the water quality standard (slightly acidic water). Similar pattern had been observed from Electrical Conductivity (EC) and Total Dissolved Solid (TDS) map, higher value of EC and TDS was dominant in the northern part of study area and lower value in the south. Groundwater taste map also revealed the identical condition with EC and TDS map which dominated by brackish and saline water in the northern part. Therefore, the study area had been divided into two zones of groundwater saline water zone possibly caused by the saltwater intrusion in the northern part and freshwater zone from the center to the southern part.

Aspects of the Geology and Hydrogeology around Awe Town, Nigeria

Awe Town, Nigeria is popular for the occurrence of brine, the brine is mined for salt production and is the major economic activity going on in the town. The occurrence of brine has however always posed a problem for domestic water supply. To avoid the salty water, public water supply scheme provided by the government is situated about 8km away from the settlement thus access to fresh water is quite difficult. The present study was initiated to study at a smaller scale, aspects of the geology and hydrogeology of the area with a view to understanding the ‘limit' of the brine issuing Awe Formation and in so doing, suggest aquiferous zones with less saline water. Geological and hydro geological mapping of the area around the town was done, which led to the production of a geological map and also a groundwater elevation contour map. In addition to this, borehole samples from four boreholes were analysed. Major ion concentration in groundwater samples was determined from XRF analysis. The main findings of the present study are that: three of the six sedimentary successions in the Benue Trough are exposed in the study area viz: Awe, Keana and Ezeaku Formations. The brine as already established by previous researchers is restricted to the Awe Formation which itself is only exposed at the core of the anticline; aquifers containing non-saline groundwater are present in sandy units of Keana and Ezeaku Formations. Groundwater in the saline region is of sodium chloride type while that in the non-saline region is of calcium bicarbonate type.

Development of a variogram procedure to identify spatial outliers using a supplemental digital elevation model

When using a ground water elevation dataset for the development of a ground water model, it is prudent to first evaluate the quality of the data before using it in a ground water model. However, it may not be practical to evaluate every data point when working with large datasets associated with a regional model. To isolate misrepresentative points in a large dataset, a graphical technique has been developed which examines the variance of ground water elevation values from an unconfined aquifer to identify points with high variance. The potential outliers identified using the graphical variogram process are subsequently evaluated by reviewing well borings, well installation records, and available time series of water level measurements to retain or reject outlier status. Supplemental ground elevation data from a digital elevation model is used to create a threshold on the experimental variogram of the ground water elevation data. This process is verified using a developed synthetic ground water dataset, then applied to a case study at the Fort Leonard Wood Military Reservation, Missouri. The method showed good results in identifying points that were justified for removal upon inspection of the available records and provides recommendations based on common causes of error. With this method’s reliance on both, an experimental variogram of measured water levels and a binned variogram of ground elevation measures, it naturally fits as a preprocessing step that can be applied prior to kriging.

Inflow and infiltration in coastal wastewater collection systems: effects of rainfall, temperature, and sea level.

Wastewater collection and treatment systems are vital to public health, economic growth, and environmental quality, but do not receive as much consideration for upgrades and improvements as other forms of public infrastructure. Extraneous inputs to a wastewater collection system are caused by rainfall and submergence ("Inflow and infiltration," I&I) and other factors, such as variation in sea level in coastal settings. These factors all pose risks for system degradation, sanitary system overflows (SSOs), and water quality impairment, but remain poorly quantified. Multiple regression analyses of total flows through 19 wastewater collection systems in coastal North Carolina, all using gravity collection systems, over a 2-year period (2010-2011) demonstrated statistically significant effects of rainfall, temperature, and sea level as drivers of extraneous flows. Rainfall effects were significant for 18/19 (95%) of these systems. Temperature effects were also significant for 18/19 (95%) of these systems. Sea level effects, primarily driven by spring-neap tidal oscillations, were significant for 11/19 (58%). Further, single factor regression analyses of the effects of temperature and sea level on system flows demonstrated significant effects for 16/19 (84%) and 18/19 (95%) systems, respectively. These collective results demonstrate the potential vulnerability of coastal wastewater collection and treatment systems to breaches in system integrity that allow extraneous flows, primarily through groundwater elevation, to drive further infrastructure degradation and environmental pollution. PRACTITIONER POINTS: Heavy rainfalls drive statistically significant inflow and infiltration (I&I) in over 90% of central wastewater systems in coastal North Carolina. Temperature, most likely as effects of seasonal variation in groundwater levels, also had a significant effect on I&I in over 90% of these systems. Sea level, expressed as daily high-high tide, drove significant effects on flow through over 90% of these systems.

Impact of sea level rise and tidal effects on flux-controlled and partially isolated shallow aquifer on the southeast coast of India.

A rise in sea level is the most important threat to the coastal aquifers in which the intensity of threat alsodepends on the local hydrogeological settings. The present study seeks to identify the impacts of sea level rise and tidal effects on the shallow and complex aquifer located south of Chennai, India. The aquifer geometry is isolated dune surfaces due to the presence of enclosing saline surface water. The freshwater is available as an elongated lens, and replenishment occurs by rainfall, with limited regional influx. Numerical simulation was carried out to understand the response of groundwater table to sea level rise until the year 2100. Initially, the tidal effects were investigated for the duration of 3years. A sinusoidal fluctuation of groundwater table is noticed only in the northern part and the tidal impact seems infinitesimal because of steep hydraulic gradient in the south. Simulation of groundwater table without considering sea level rise predicts a decline in the elevation of groundwater table/freshwater lens by - 0.35m in the dune surfaces. The simulation with reported sea level rise of 2mmyear-1 with the same rate of groundwater pumping results in a total increase of 0.5m in groundwater table. The study infers that the tidal effects are high in the shallow groundwater gradient, and sea level rise will be beneficial to the isolated coastal freshwater aquifers by increasing the elevation of groundwater table/freshwater lens and further deepening the interface between seawater and freshwater.

FLOOD DISASTER INVESTIGATION BASED ON CORRELATION OF QUANTITATIVE GEOMORPHOLOGY AND GROUNDWATER LEVEL IN CINTARATU VILLAGE, PANGANDARAN REGENCY, WEST JAVA PROVINCE, INDONESIA

Recently, a flood disaster is occurred in Cintaratu Village, Parigi Sub-district, Pangandaran Regency of West Java Province. Geomorphologically, the watershed systems of this area consist of Cintaratu, Selasari dan Cintakarya. Geologically, the study area is composed by calcarenite, reef limestone, and clastic limestone which is susceptible to dissolution when contact with the water. This research was conducted to investigate the causes of flood disaster based on the correlation between quantitative geomorphology and groundwater level analysis. The methods for this research are field observation and studio analysis. Field observation were conducted by hydro-geological mapping to determine the groundwater level and, also, the lithology of the surrounded area. Studio analyses include the calculation of Bifurcation Ratio (Rb), Drainage Density (Dd), and Fault Fracture Density (FFD). Based on Bifurcation Ratio calculation, the value of Rb1-2 of Cintaratu, Selasari, and Cintakarya Watershed respectively are 2.8, 6, and 3.5. Generally, Cintaratu Watershed has the lowest Rb value, and thus has the highest potential to be flooded. Groundwater flow map shows that the stream accumulation zone is located at the center due to topography controlled, thus allows water to accumulate. The average elevation of groundwater is is 111.3871 masl, however, the the average elevation of the ground is 117.4706 masl. The difference of both value is 6.083529 m. This shows that undersaturated area between groundwater elevation and ground elevation is low. So it can be concluded that, the main causes of flood disaster either from above or underground can be investigated by the correlation between quantitative geomorphology analysis and groundwater level.

Using Water Injection to Prevent Shaft Failure in the Jining No. 3 Coal Mine, China

Water injection into aquifers is a new approach for preventing shaft failure by stabilizing water levels. A series of injection tests was performed in the Jining no. 3 coal mine. Injection flow rates decreased over time as the water injection channels were blocked. Groundwater elevations in four observation boreholes and strain variations in the alluvial strata and shaft walls were analyzed to assess the effect of water injection on shaft failure and determine a preventive injection rate. The groundwater elevations in the observation boreholes decreased and the compressive strains in the alluvial strata and shaft wall increased overall over time. Although the water injection effect has weakened in recent years, it has still effectively slowed the increase of compressive strain in the shaft wall compared with conditions before water injection. We determined that the total and average injection rates for the four boreholes need to be approximately 20 m3/h and ≥ 5 m3/h, respectively, to maintain groundwater elevations and stabilize strain in the shafts. Measures such as oscillating pressurized water injection or increasing the number of injection boreholes could be used to increase injection flow rates and prevent shaft failure.