Selecting Between One‐Dimensional and Two‐Dimensional Hydrodynamic Models for Ecohydraulic Analysis

Aquatic habitat assessment and river restoration design require geospatially explicit maps of hydraulic conditions. Diverse mechanistic ecohydraulic models compute spatially explicit depth and velocity results to evaluate habitat suitability spatially as a function of these abiotic conditions. This study compared depth and velocity results from two‐dimensional (2D) and one‐dimensional (1D) hydraulic models with algorithms that laterally discretize 1D velocity and interpolate depth and velocity spatially based on the Laplacian heat mapping approach. These ‘conveyance distributed’ methods constitute ‘best 1D modelling practice’ and were compared with 2D results for the first time. The 1D and 2D models were applied to three morphologically distinct reaches (leveed, meandering, and anastomosing) for three flows (base, bankfull, and flood flows) of the partially regulated, gravel/cobble lower Yuba River in north–central California. The test metrics were the coefficient of determination (R²) and the median absolute residual ( ). These metrics quantified the incremental uncertainty 1D approximation incurs, results which make explicit cost–benefit processes of model selection possible. Finally, velocity residual maps were analysed to identify regions and processes where residuals were high, indicating divergence from the 1D assumptions. Paired data (1D–2D) fell between 0.94 ≥ R² ≥ 1.00 (R²_mean = 0.98 and R²_median = 0.99) for depth and median absolute residuals were all 3.8 ≤ ≤ 7.2% (i.e. 50% of residuals are approximately within ±1.7 to 3.6%). Higher flows and lower gradient reaches had lower residuals and higher R². Velocity diverged more, particularly for base flow in anastomosing reaches (0.42 < R² < 0.58). One‐dimensional, conveyance distributed, assumptions performed better for other channel types, where 0.69 < R² < 0.81 (R²_mean = 0.75 and R²_median = 0.77), with median absolute residuals between 9.6% > > 22.4% (i.e. ~ ± 4.6 to ±11.2%), where _mean = 14.2% and _median = 13% (~ ±7.1 and 6.5%). The conveyance distributed 1D velocity model performed best, where the orthogonal flow assumptions obtained and where side channels did not transition from backwater to conveying area between flows. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of cover on mean column hydraulic characteristics in small pool riffle morphology streams

The field of ecohydraulics tries to link biological‐ and physical‐based processes in order to describe better the distribution of plants and animals in rivers. We tested the hypothesis that the influence of cover in pools and riffles would not be detectable using average velocity, turbulent kinetic energy and turbulent intensity, and compared these measurements to locations distant from cover. We measured water velocity fluctuations using an acoustic Doppler velocimeter. We found that turbulent intensity in the downstream direction (u′) and the transverse or cross‐stream direction (v′) were the most useful in detecting the presence of cover in pools and riffles. Differences were apparent between locations near cover in pools and riffles. Turbulent kinetic energy (k) and vertical turbulent intensity (w′) detected cover in pools but not in riffles. Average downstream velocity ( ) detected cover in riffles but not in pools. Average cross‐stream ( ) and vertical ( ) velocities did not detect any differences at all. We rejected the null hypothesis and concluded that turbulence caused by habitat features such as large rocks, wood or other channel complexities results in a statistically meaningful difference in flow characteristics in locations near cover. This finding was tempered by the fact that knowledge about how fish respond to turbulence is limited in comparison to our understanding of average velocity values. Despite the potential benefits to habitat modelling of incorporating turbulence‐based metrics, application of these findings will be challenging because turbulence modelling is difficult and current models may not be appropriate for application to rivers. Copyright © 2007 John Wiley & Sons, Ltd.     

Patterns in groundwater nitrogen concentration in the riparian zone of a large semi‐arid river (River Murray,Australia)

Lateral exchanges of surface water between river channels and their floodplains are important for vegetation health and aquatic food‐web productivity in semi‐arid ecosystems. However, the significance of the lateral connectivity via sub‐surface pathways in these systems is not as well understood. Patterns in nitrogen concentration in groundwater and in the unsaturated zone were used to infer the sub‐surface biogeochemistry of N in the riparian zone of a large semi‐arid floodplain (Hattah‐Kulkyne National Park) of the River Murray, Australia. The riparian zone plays a special role in this system as it is an area of transition between fresh surface waters and saline floodplain groundwater. The river was losing water to the floodplain during baseflow conditions but gradients were temporarily reversed following floods. In general, the redox conditions were sub‐oxic to anoxic in riparian groundwater and the main forms of N present were NH and dissolved organic N. There was a gradient in NH concentration from the river to the floodplain, suggesting that the main source of NH was from the decomposition of organic matter in fluvial sediments. Elevated concentrations of NO were occasionally found in shallow groundwater away from the river following floods but tended not to persist. The source of the NO appeared to be unsaturated‐zone NO displaced to the water table during floods. Assuming that denitrification was the main attenuation process, this displacement of unsaturated zone NO to anoxic groundwater could be a significant N removal process from the ecosystem (estimated at 18 kg N ha^?1 for the largest flood during the study). Understanding the impact of river regulation on floodplain nutrient cycles in River Murray floodplains will be challenging because the changes in floodplain hydrology are complex and coincide with salinization of soils and groundwater. Copyright © 2005 John Wiley & Sons, Ltd.     

Nitrogen dynamics in sediment during water level manipulation on the Upper Mississippi River

Nitrogen (N) has been linked to increasing eutrophication in the Gulf of Mexico and as a result there is increased interest in managing and improving water quality in the Mississippi River system. Water level reductions, or ‘drawdowns’, are being used more frequently in large river impoundments to improve vegetation growth and sediment compaction. We selected two areas of the Upper Mississippi River system (Navigation Pool 8 and Swan Lake) to examine the effects of water level drawdown on N dynamics. Navigation Pool 8 experienced summer drawdowns in 2001 and 2002. Certain areas of Swan Lake have been drawn down annually since the early 1970s where as other areas have remained inundated. In the 2002 Pool 8 study we determined the effects of sediment drying and rewetting resulting from water level drawdown on (1) patterns of sediment nitrification and denitrification and (2) concentrations of sediment and surface water total N (TN), nitrate, and ammonium (NH). In 2001, we only examined sediment NH and TN. In the Swan Lake study, we determined the long‐term effects of water level drawdowns on concentrations of sediment NH and TN in sediments that dried annually and those that remained inundated. Sediment NH decreased significantly in the Pool 8 studies during periods of desiccation, although there were no consistent trends in nitrification and denitrification or a reduction in total sediment N. Ammonium in sediments that have dried annually in Swan Lake appeared lower but was not significantly different from sediments that remain wet. The reduction in sediment NH in parts of Pool 8 was likely a result of increased plant growth and N assimilation, which is then redeposited back to the sediment surface upon plant senescence. Similarly, the Swan Lake study suggested that drawdowns do not result in long term reduction in sediment N. Water level drawdowns may actually reduce water retention time and river‐floodplain connectivity, while promoting significant accumulation of organic N. These results indicate that water level drawdowns are probably not an effective means of removing N from the Upper Mississippi River system. Copyright © 2006 John Wiley & Sons, Ltd.     

Seasonal variation in nutrient retention during inundation of a short‐hydroperiod floodplain

Floodplains are generally considered to be important locations for nutrient retention or inorganic‐to‐organic nutrient conversions in riverine ecosystems. However, little is known about nutrient processing in short‐hydroperiod floodplains or seasonal variation in floodplain nutrient retention. Therefore, we quantified the net uptake, release or transformation of nitrogen (N), phosphorus (P) and suspended sediment species during brief periods (1–2 days) of overbank flooding through a 250‐m floodplain flowpath on the fourth‐order Mattawoman Creek, Maryland U.S.A. Sampling occurred during a winter, two spring and a summer flood in this largely forested watershed with low nutrient and sediment loading. Concentrations of NO increased significantly in surface water flowing over the floodplain in three of the four floods, suggesting the floodplain was a source of NO. The upper portion of the floodplain flowpath consistently exported NH, most likely due to the hyporheic flushing of floodplain soil NH, which was then likely nitrified to NO in floodwaters. The floodplain was a sink for particulate organic P (POP) during two floods and particulate organic N and inorganic suspended sediment (ISS) during one flood. Large releases of all dissolved inorganic N and P species occurred following a snowmelt and subsequent cold winter flood. Although there was little consistency in most patterns of nutrient processing among the different floods, this floodplain, characterized by brief inundation, low residence time and low nutrient loading, behaved oppositely from the conceptual model for most floodplains in that it generally exported inorganic nutrients and imported organic nutrients. Published in 2007 by John Wiley & Sons, Ltd.     

The effect of marine and Aral Sea water on the salinity tolerance of three Paramecium species (Ciliophora)

The shift of salinity tolerant ranges in three species of ciliates Paramecium caudatum, P. primaurelia and P. jenningsi was studied in waters containing a composition of salts resembling those in the Aral Sea, in comparison with composition of salts in marine waters. The results indicate that the salt values of tolerant ranges are increasing in water with the Aral Sea composition. The ratio among values of tolerant ranges is described by a linear function. A similar ratio connecting the same tolerant ranges exists in ciliates, but leads to reliable values of tolerant ranges when expressed in terms of chlorine concentration. Thus, the connection between the tolerances of aquatic organisms obtained for water of marine composition and water of continental composition might be described by the equation , where S_m = tolerance of organisms in marine water, whereas S_k = tolerance of organisms in continental saline water. The term α indicates the portion of chlorine ion continental saline water, while β indicates the portion in marine water.     

Role of Local Flow Conditions in River Biofilm Colonization and Early Growth

Direct numerical simulations of a turbulent boundary layer flow over a bed of hemispheres of height h are performed using an immersed boundary method for comparison with river biofilm growth experiments performed in a hydraulic flume. Flow statistics above the substrates are shown to be in agreement with measurements performed by laser Doppler velocimetry and particle image velocimetry in the experiments. Numerical simulations give access to flow components inside the roughness sublayer, and biofilm colonization patterns found in the experiments are shown to be associated with low shear stress regions on the hemisphere surface. Two bed configurations, namely staggered and aligned configurations, lead to different colonization patterns because of differences in the local flow topology. Dependence with the Reynolds number of the biofilm distribution and accrual 7 days after inoculum is shown to be associated to local flow topology change and shear stress intensity. In particular, the shear stress τ on the surface of the hemispheres is found to scale as , where Re_t = u^*h/ν, with u^* as the log law friction velocity and ν as the fluid kinematic viscosity. This scaling is due to the development of boundary layers along the hemisphere surface. Associated with a critical shear stress for colonization and early growth, it explains the increasing delay in biomass accrual for increasing flow velocities in the experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Water quality in the southern Tibetan Plateau: chemical evaluation of the Yarlung Tsangpo (Brahmaputra)

Yarlung Tsangpo (Brahmaputra) is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau. It remains one of only two large non‐regulated rivers in China. In this paper the chemical composition of Yarlung Tsangpo and its major tributaries (Raga Tsangpo, Nyangchu and Lhasa River) are studied. Water samples (n = 55) were collected and measured for major ions, trace elements and nutrients in order to: (1) define the present chemical quality of this water course; (2) address possible mechanisms governing the water chemical compositions, and (3) identify potential sources for contaminants. Multivariable analysis shows that geology and climate are the major explanatory variables for the spatial variation in water chemistry in this river system. In general, water chemistry is mainly controlled by carbonate weathering, with Ca²⁺ and HCO being the dominant ions. In addition, runoff from brackish/saline lakes and geothermal waters, enriched in Na⁺, Cl^?, SO, Mg²⁺ and Li, are major contributors of elevated concentrations of these solutes in the headwater regions resulting in a relatively high loading of total dissolved solids (TDS, 146–397 mg L^?1). Levels of most heavy metals and total dissolved nutrients were generally found to be low. However, elevated As concentration (avg. 95 μg L^?1) in the headwaters and additions from untreated wastewater were evident at some locations. Copyright © 2009 John Wiley & Sons, Ltd.     

Nitrogen processing by biofilms along a lowland river continuum

While numerous studies have examined N dynamics along a river continuum, few have specifically examined the role of biofilms. Nitrogen dynamics and microbial community structure were determined on biofilms at six sites along a 120 km stretch of the lowland Ovens River, South Eastern Australia using artificial substrates. Terminal restriction fragment length polymorphism (T‐RFLP), chlorophyll a and protein analyses were used to assess biofilm microbial community composition. N dynamics was determined on the biofilms using the acetylene (C₂H₂) block technique and assessing changes in NH, NO_x and N₂O. Unlike microbial community structure, N dynamics were spatially heterogeneous. Nitrification, determined from the difference in accumulation of NH before and after addition of C₂H₂, occurred mostly in the upper sites with rates up to 1.4 × 10^?5 mol m^?2 h^?1. The highest rates of denitrification occurred in the mid‐reaches of the river (with rates up to 1 × 10^?5 mol m^?2 h^?1) but denitrification was not detected in the lower reaches. At the very most, only 50% of the observed uptake of NO_x by the biofilms following addition of C₂H₂ could be accounted for by denitrification. Copyright © 2005 John Wiley & Sons, Ltd.     

Nitrate removal in the hyporheic zone of a salmon river in Alaska

Pacific boreal streams and riparian zones are believed to receive significant N loads that are derived from the ocean in the form of decaying sockeye salmon (Oncorhynchus nerka). Using a small stream in south‐central Alaska we examined whether the associated riparian forest could take up the pulse of marine‐derived nitrogen (MDN) entering the hyporheic zone from spawning and dying sockeye salmon. We evaluate the relative importance of riparian uptake and denitrification in nitrate‐N removal in hyporheic sediment. We found that maximum biological removal of nitrate peaked within 1 h of water entering the hyporheic zone, decreasing exponentially with subsurface flow duration. Plant and microbial uptake reached 14 µg NO‐N L^?1 min^?1 and denitrification reached 4 µg NO‐N L^?1 min^?1 during the initial 2 h of transit time. Our results reinforce the hypothesis that MDN from Pacific salmon can be transferred to riparian zone via hyporheic flow. Most nitrate‐N removal along hyporheic flow paths is by plant and microbial uptake (the respective contributions could not be determined). Denitrifying bacteria are present and active in the hyporheic zones of this well‐oxygenated Alaskan stream but their contribution to the nitrate‐N removal is small compared to plant and microbial uptake in such nitrate‐N poor environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Role of a cascade of reservoirs in regulating downstream transport of sediment,carbon and nutrients: Case study of tropical arid climate Tana River Basin

Mass balances for dissolved and particulate organic C (DOC and POC), particulate nitrogen (PN) and dissolved inorganic nitrogen (DIN), dissolved and dissolved Si (DSi) were estimated by considering the annual fluxes in and out of three cascading reservoirs (Masinga, Kamburu and Gitaru) on the Tana River, Kenya. Flux data were obtained through biweekly sampling of the main inflows and outflows of the three reservoirs between May 2011 and May 2013. The degree of retention of particulate and dissolved materials generally was higher in Masinga Reservoir, compared to Kamburu and Gitaru reservoirs, which could be attributable to the much higher water retention time (i.e., 163, 19 and 3 days for Masinga, Kamburu and Gitaru, respectively, in 2012; 136, 14 and 2 days for Masinga, Kamburu and Gitaru reservoirs, respectively, in 2013). It was also observed the two smaller reservoirs (Kamburu and Gitaru) did not always act as net sinks of materials, but occasionally were a net source of materials transported downstream. The role of reservoirs in material retention was also found to exhibit interannual variability, likely controlled by the total annual water discharge into the reservoirs.     

Evaluation of Owabi Reservoir (Ghana) water quality using factor analysis

The Owabi Reservoir receives water inflows from several streams that drain through the rapidly urbanizing towns in the Kumasi metropolis. The reservoir catchment had been encroached upon by various human activities, resulting in the generation of large volumes of waste water being discharged into streams draining to the reservoir. This study presents a comprehensive evaluation of the water quality of Owabi Reservoir. Water samples from 10 sampling sites within the reservoir were analysed for various water quality parameters; namely, pH, electrical conductivity (EC), sulphate (), phosphate (), chloride (Cl^?), lead (Pb), arsenic (As), zinc (Zn), iron (Fe), copper (Cu), total dissolved solids (TSS), turbidity, faecal coliform and E. coli. The measured water quality parameters were compared to the guidelines proposed by the WHO for drinking water and natural background levels. Mean values for Pb, As, turbidity, TDS, faecal coliform and E. coli were greater than the WHO guidelines. Factor analysis for the measured parameters resulted in the extraction of five factors accounting for 83.13% of the total variance. Factor 1 showed strong loadings for , and TDS, reflecting a negative influence on the water quality by agricultural discharges. Factor 2 showed high loadings for EC, Cl^? and apparent colour, while Factor 3 registered high loadings for colour and faecal coliform, suggesting domestic wastewater discharges and the presence of decaying organic matter. Factors 4 and 5 showed high loadings for copper, lead, turbidity and E. coli, an indication of both organic and inorganic pollution. Accordingly, periodic monitoring of Owabi Reservoir water quality, and the streams draining into it, is recommended as a means of ensuring good water quality, as well as facilitating the identification of the possible types and sources of water pollutants entering the reservoir.     

Seasonal and spatial variations in major and trace elements in a regulated boreal river (Esse River) affected by acid sulphate soils

In coastal areas of Finland, extensive artificial drainage of Holocene sulphide‐bearing marine and lacustrine sediments has resulted in development of acid sulphate (AS) soils (pH 2.5–4.5) over an estimated area of approximately 3000 km². During heavy rains and snow melting, these soils are flushed resulting in discharge of acidic and metal‐rich waters that strongly affect small streams. However, the total and precise effects in the important and large rivers are not well understood. In this study, the impact of AS soil occurrence and hydrological changes on water quality was determined in an important regulated boreal river (Esse River) having a catchment area of 2054 km² partially covered with AS soil (39 km²). Water samples, collected at five sites along the river during four carefully selected events, were analysed for pH, total organic carbon, conductivity and the following elements/anions: Al, Ba, Br, Ca, Cd, Cl^?, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, NO, Rb, Sc, Si, SO, Sr, Th, Y and Zn. There is a clear spatial correlation between AS soil occurrence and elevated element concentrations in the river water, especially when the conditions change from dry/warm (summer) to wet/cool (autumn). During the rains in autumn these soils are extensively flushed and concentrations of Co, La, Zn, Y, Mn and Al are increased between three and nine times towards the outlet. The buffering capacity of the river was, however, high enough to prevent a detrimental drop in pH. Another intriguing feature is substantially elevated concentrations of several potentially toxic metals (Cr, Cd, Cu) in the middle reaches in winter when the river is ice‐covered. Since no external source for this was found, we suggest an internal source operating by an as yet unknown mechanism. During baseflow in summer, the concentrations of several solutes reach minimum concentrations. Copyright © 2005 John Wiley & Sons, Ltd.     

THE INFLUENCE OF DIFFERENT DESIGN PARAMETERS AND WORKING CONDITIONS ON CHARACTERISTICS OF HEAT METERS

In this article,the UDF technology in Fluent software is used to simulate three-dimensional flow fields and to obtain various flow parameters. The standard k-ε model and the RNG k-ε model are both used to calculate the inner flow field of the basal meter,and a comparison of the calculated results between two models shows that RNG k-ε model is more effective for calculations of the inner flow of rotary wing mechanism. The influence of tip clearance on the characteristics of the basal meter is studied. The in...     

Eutrophication of lakes in urbanized areas: The case of Yaounde Municipal Lake in Cameroon, Central Africa

A 1 year qualitative and quantitative evaluation of phytoplankton and chlorophyll‐a, as well as some physicochemical parameters, was recorded in a shallow tropical lake in Cameroon: the Yaounde Municipal Lake. Physicochemical measurements also were regularly made in its main tributary (Mingoa Stream). These analyses aimed to assess the lake's trophic status and to propose measures for controlling its degradation process. The Secchi disk transparency was low and rarely exceeded 100 cm. Conductivity was higher near the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from a 2.5 m depth leads to high quantities of ammonium‐nitrogen. The total phosphorus concentrations varied from 80–2290 µg P L^?1 and the total Kjeldhal nitrogen concentrations fluctuated between 3 and 15 mg  L^?1. Upstream to the lake, in the Mingoa Stream, total phosphorus concentrations ranged from 0.6–3.8 mg P L^?1 and total Kjeldhal nitrogen concentrations ranged from 10–22 mg  L^?1. There are up to 102 phytoplankton‐specific taxa, with Euglenophyta and Chlorophyta particularly more diversified. The phytoplankton biomass and chlorophyll‐a concentrations reached 225 µg mL^?1 and 566 mg m^?3, respectively. The analyses pointed out the allogenic nature of the functioning of this ecosystem as a result of bad waste management in the surrounding landscape. Urgent actions need to be undertaken in order to rehabilitate this lake, which rapidly shifted to a hypertrophic status.     

Fenton-like oxidation of azo dye in aqueous solution using magnetic Fe3O4-MnO2 nanocomposites as catalysts

In order to overcome the drawback of the low degree of separation from an aqueous solution of MnO_2, Fe_3 O_4-MnO_2 core-shell nanocomposites were used as heterogeneous Fenton-like catalysts for the removal of acid orange 7. On the basis of the catalyst characterization, the catalytic ability of the as-synthesized nanocomposites was examined. The results showed that Fe304-Mn02 core-shell nanocomposites had greater catalytic ability than Fe_3 O_4 or MnO_2 used alone. Meanwhile, the catalyst dosage, H_2 O_2 dosage, temperature, and initial pH had significant effects on the removal of acid orange 7. A high degree of stability and reusability were exhibited by Fe_3 O_4-MnO_2 core-shell nanocomposites. Both HO· and HO_2· were generated in the reaction and HO· was the main radical for the removal of acid orange 7. A mechanism for H_2 O_2 catalytic decomposition using Fe_3 O_4-MnO_2 core-shell nanocomposites to produce HO·is proposed.     

Water table fluctuation with a random initial condition

The nonlinear Boussinesq equation is used to understand water table fluctuations in various ditch drainage problems. An approximate solution of this equation with a random initial condition and deterministic boundary conditions, recharge rate and aquifer parameters has been developed to predict a transient water table in a ditch-drainage system. The effects of uncertainty in the initial condition on the water table are illustrated with the help of a synthetic example. These results would find applications in ditch-drainage design.Notation A / tanh t - a lower value of the random variable representing the initial water table height at the mid point - a+b Upper value of the random variable representing the initial water table height at the midpoint - B tanh t - C 4/ - h variable water table height - h mean of the variable water table height - h _m variable water table height at the mid point - h _m mean of the variable water table height at the mid point - K hydraulic conductivity - L half spacing between the ditches - m ₀ initial water table height at the mid point - N Uniform rate of recharge - S specific yield - t time of observation - x distance measured from the ditch boundary - (4/SL)(NK)^1/2 - (L/4)(N/K)^1/2 - dummy integral variable     

Time-dependent soil-water distribution under a circular trickle source

Soil-water distribution in homogeneous soil profiles of Yolo clay loam and Yolo sand (Typic xerorthents) irrigated from a circular source of water, was measured several times after the initiation of irrigation. The effect of trickle discharge rates and soil type on the locations of the wetting front and soil-water distribution was considered. Soil-water tension and hydraulic conductivity, as functions of soil-water content, were also measured. The theories of time-dependent, linearized infiltration from a circular source and a finite-element solution of the two-dimensional transient soil-water equation were compared with the experimental results. In general, for both soils the computer horizontal and vertical advances of the wetting front were closely related to those observed. With both theories, a better prediction of the wetting front position for the clay loam soil than for the sandy soil is shown. The calculated and measured horizontal vertical advances did not agree over long periods of time. With the linearized solution, overestimated and underestimated vertical advances for the clay and sandy soils, respectively, were shown. The finite-element model approximate in a better way the vertical advances than the linearized solution, while an opposite tendency for the horizontal advances indicated, especially in sandy soil.Notation k constant (dK/d) - K hydraulic conductivity - K ₀ saturated hydraulic conductivity - J ₀,J ₁ Bessel functions of the first kind - h soil water tension - q Q/r ₀ ² - Q discharge rate - r cylindrical coordinate; also horizontal distance in soil surface - R dimensionless quantity forr - r ₀ constant pond radius - R ₀ dimensionless quantity forr ₀ - t time - T dimensionless quantity fort - x, y Cartesian coordinates - z vertical coordinate; also vertical distance along thez axis chosen positively downward - Z dimensionless quantity forz - empirical soil characteristic constant - dummy variable of integration - volumetric soil water content - matrix flux potential - dimensionless quantity for      

Determining Hydraulic Characteristics of Production Wells using Genetic Algorithm

Proper well management requires the determination of characteristic hydraulic parameters of production wells such as well loss coefficient (C) and aquifer loss coefficient (B), which are conventionally determined by the graphical analysis ofstep-drawdowntest data. However, in the present study, the efficacy of a non-conventional optimization technique called Genetic Algorithm (GA), which ensures near-optimal or optimal solutions, is assessedin determining well parameters from step-drawdown test data. Computer programs were developed to optimize the well parametersby GA technique for two cases: (i) optimization of B and C only, and (ii) optimization of B, C and p (exponent) as well as to evaluate the well condition. The reliability and robustness of the developed computer programs were tested usingnine sets of published and unpublished step-drawdown data from varying hydrogeologic conditions. The well parameters obtained by the GA technique were compared with those obtained by the conventional graphical method in terms of root mean square error(RMSE) and visual inspection. It was revealed that the GA technique yielded more reliable well parameters with significantlylow values of RMSE for almost all the datasets, especially in caseof three-variable optimization. The optimal values of the parametersB, C and p for the nine datasets were found to range from 0.382 to 2.292 min m^-2, 0.091 to 3.262, and 1.8 to 3.6, respectively. Because of a wide variation of p, the GA techniqueresulted in considerably different but dependable and robust well parameters as well as well specific capacity and well efficiency compared to the graphical method. The condition of three wells was found to be good, one well bad and that of the remaining five wells satisfactory. The performance evaluation of the developed GA code indicated that a proper selection of generation number and population size is essential to ensure efficient optimization. Furthermore,a sensitivity analysis of the obtained optimal parameters demonstrated that the GA technique resulted in a unique set ofthe parameters for all the nine datasets. It is concluded thatthe GA technique is an effective and reliable numerical tool for determining the characteristic hydraulic parameters of production wells.     

NUMERICAL MODELLING OF FREE-SURFACE FLOWS WITH BOTTOM AND SURFACE-LAYER PRESSURE TREATMENT

A new non-hydrostatic numerical model with the three-dimensional Navier-Stokes equations on structured grids was constructed and discussed. The algorithm is based upon a staggered finite difference Crank-Nicholson scheme on a Cartesian grid. The eddy viscosity coefficient was calculated by the efficient k-ε turbulence model. A new surface-layer non-hydrostatic treatment and a local cell bottom treatment were introduced so that the three-dimensional model is fully non-hydrostatic and is free of any hydrostat...