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Table Depth (table + depth)

Distribution by Scientific Domains
Engineering72%
Life Sciences11%
Earth and Environmental Science11%

Kinds of Table Depth

  • water table depth
    		•

    Selected Abstracts

    Sensitivity of Stream flow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed,

    JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010
    Zhaohua Dai
    Dai, Zhaohua, Carl C. Trettin, Changsheng Li, Devendra M. Amatya, Ge Sun, and Harbin Li, 2010. Sensitivity of Streamflow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed. Journal of the American Water Resources Association (JAWRA) 1,13. DOI: 10.1111/j.1752-1688.2010.00474.x Abstract:, A physically based distributed hydrological model, MIKE SHE, was used to evaluate the effects of altered temperature and precipitation regimes on the streamflow and water table in a forested watershed on the southeastern Atlantic coastal plain. The model calibration and validation against both streamflow and water table depth showed that the MIKE SHE was applicable for predicting the streamflow and water table dynamics for this watershed with an acceptable model efficiency (E > 0.5 for daily streamflow and >0.75 for monthly streamflow). The simulation results from changing temperature and precipitation scenarios indicate that climate change influences both streamflow and water table in the forested watershed. Compared to current climate conditions, the annual average streamflow increased or decreased by 2.4% with one percentage increase or decrease in precipitation; a quadratic polynomial relationship between changes in water table depth (cm) and precipitation (%) was found. The annual average water table depth and annual average streamflow linearly decreased with an increase in temperature within the range of temperature change scenarios (0-6°C). The simulation results from the potential climate change scenarios indicate that future climate change will substantially impact the hydrological regime of upland and wetland forests on the coastal plain with corresponding implications to altered ecosystem functions that are dependent on water. [source]

    A low-dimensional physically based model of hydrologic control of shallow landsliding on complex hillslopes

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008
    Ali Talebi
    Abstract Hillslopes have complex three-dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and soil depth. To investigate the stability of complex hillslopes (with different slope curvatures and plan shapes), we combine the hillslope-storage Boussinesq (HSB) model with the infinite slope stability method. The HSB model is based on the continuity and Darcy equations expressed in terms of storage along the hillslope. Solutions of the HSB equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. The presented model is composed of three parts: a topography model conceptualizing three-dimensional soil mantled landscapes, a dynamic hydrology model for shallow subsurface flow and water table depth (HSB model) and an infinite slope stability method based on the Mohr,Coulomb failure law. The resulting hillslope-storage Boussinesq stability model (HSB-SM) is able to simulate rain-induced shallow landsliding on hillslopes with non-constant bedrock slope and non-parallel plan shape. We apply the model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). In the presented model, the unsaturated storage has been calculated based on the unit head gradient assumption. To relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case, we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method. The results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability. Therefore, it can be concluded that the presented dynamic slope stability model (HSB-SM) can be used safely for slope stability analysis on complex hillslopes. Our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others, whilst divergent convex hillslopes remain stable (even after intense rainfall). In addition, the relation between subsurface flow and hillslope stability has been investigated. Our analyses show that the minimum safety factor (FS) occurs when the rate of subsurface flow is a maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    The contribution of bryophytes to the carbon exchange for a temperate rainforest

    GLOBAL CHANGE BIOLOGY, Issue 8 2003
    Evan H. DeLucia
    Abstract Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100,400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis , whole-plant respiration) per unit ground area at saturating irradiance was 1.9 ,mol m,2 s,1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m,2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ,1010 g m,2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ,11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [source]

    Vapor Intrusion in Homes over Gasoline-Contaminated Ground Water in Stafford, New Jersey

    GROUND WATER MONITORING & REMEDIATION, Issue 1 2006
    Paul F. Sanders
    The potential for chemical vapor intrusion from contaminated ground water to the interior of homes was investigated at a site with a leaking underground gasoline storage tank in Stafford Township, New Jersey. This location exhibited conditions favorable to vapor intrusion, with sand soil and a water table depth of 3.3 m. Concentrations of volatile organic chemicals in the ground water were as high as 82 mg/L for total benzene, toluene, ethylbenzene, and xylene (BTEX) and up to 590 mg/L for methyl- t -butyl ether (MTBE). Soil vapor samples at multiple depths were taken adjacent to several homes. Inside the homes, air samples were taken on the main floor, in the basement, and under the foundation slab. Despite high ground water concentrations, only one home had measurable impacts to indoor air quality attributable to some of the ground water contaminants. In this house, the BTEX chemicals were not detected in the basement, indicating a lack of indoor air impacts from the ground water for these chemicals. Oxygen measurements suggested that degradation attenuated these chemicals as they diffused through the vadose zone. However, MTBE, 2,2,4-trimethylpentane (isooctane), and cyclohexane were found in the indoor air. The first two of these chemicals served as gasoline-specific tracers and indicated that vapor intrusion was occurring. Attenuation factors (the ratio of the indoor air concentration to a source soil vapor concentration) for the BTEX chemicals between the ground water and the indoor air were <1 × 10,5, and for MTBE was 1.2 × 10,5. Attenuation factors between the deep-soil vapor and the basement air were as follows: BTEX compounds, <1 × 10,5; MTBE, 2.2 × 10,5; 2,2,4-trimethylpentane, 3.6 × 10,4; and cyclohexane, 1.2 × 10,4. Attenuation factors between the subslab vapor and the basement air were 7 to 8 × 10,3. [source]

    Water table fluctuations under three riparian land covers, Iowa (USA)

    HYDROLOGICAL PROCESSES, Issue 18 2007
    Keith E. Schilling
    Abstract Water table depth is known to play an important role in nitrogen cycling in riparian zones, but little detailed monitoring of water table fluctuations has been reported. In this study, results of high-resolution water table monitoring under three common riparian land covers (forest, cool season grass, corn) were analysed to gain a better understanding of the relation of vegetation cover to water table depth. Three riparian wells located at the Neal Smith National Wildlife Refuge in Jasper County, Iowa, were instrumented with data loggers to record hourly water table behaviour from July to December 2004. Water table depth under the forest showed a diurnal pattern of rising and falling water levels, whereas the grass and corn exhibited a stepped pattern of greater drawdown during the day and less drainage at night. Clear daytime and night-time water table signals were related to daily plant water demands and lateral groundwater flow. Using two estimates of specific yield, hourly and daily ET rates were estimated to be higher under the forest cover than the grass and corn, with peak ET rates in July ranging from 5·02 to 6·32 mm day,1 for forest and from 1·81 to 4·13 mm day,1 for corn and grass. Following plant senescence in October, water table declines were associated with lateral flow to Walnut Creek. The results from this study suggest that consideration should be given to monitoring water table behaviour more frequently to capture daily and seasonal patterns related to riparian vegetation type. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Application of the distributed hydrology soil vegetation model to Redfish Creek, British Columbia: model evaluation using internal catchment data

    HYDROLOGICAL PROCESSES, Issue 2 2003
    Andrew Whitaker
    Abstract The Distributed Hydrology Soil Vegetation Model is applied to the Redfish Creek catchment to investigate the suitability of this model for simulation of forested mountainous watersheds in interior British Columbia and other high-latitude and high-altitude areas. On-site meteorological data and GIS information on terrain parameters, forest cover, and soil cover are used to specify model input. A stepwise approach is taken in calibrating the model, in which snow accumulation and melt parameters for clear-cut and forested areas were optimized independent of runoff production parameters. The calibrated model performs well in reproducing year-to-year variability in the outflow hydrograph, including peak flows. In the subsequent model performance evaluation for simulation of catchment processes, emphasis is put on elevation and temporal differences in snow accumulation and melt, spatial patterns of snowline retreat, water table depth, and internal runoff generation, using internal catchment data as much as possible. Although the overall model performance based on these criteria is found to be good, some issues regarding the simulation of internal catchment processes remain. These issues are related to the distribution of meteorological variables over the catchment and a lack of information on spatial variability in soil properties and soil saturation patterns. Present data limitations for testing internal model accuracy serve to guide future data collection at Redfish Creek. This study also illustrates the challenges that need to be overcome before distributed physically based hydrologic models can be used for simulating catchments with fewer data resources. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    The simulation of heat and water exchange at the land,atmosphere interface for the boreal grassland by the land-surface model SWAP

    HYDROLOGICAL PROCESSES, Issue 10 2002
    Yeugeniy M. Gusev
    Abstract The major goal of this paper is to evaluate the ability of the physically based land surface model SWAP to reproduce heat and water exchange processes that occur in mid-latitude boreal grassland regions characterized by a clear seasonal course of hydrometeorological conditions, deep snow cover, seasonally frozen soil, as well as seasonally mobile and shallow water table depth. A unique set of hydrometeorological data measured over 18 years (1966,83) at the Usadievskiy catchment (grassland) situated in the central part of Valdai Hills (Russia) provides an opportunity to validate the model. To perform such validation in a proper way, SWAP is modified to take into account a shallow water table depth. The new model differs from its previous version mainly in the parameterization of water transfer in a soil column; besides that, it includes soil water,groundwater interaction. A brief description of the new version of SWAP and the results of its validation are presented. Simulations of snow density, snow depth, snow water equivalent, daily snow surface temperature, daily evaporation from snow cover, water yield of snow cover, water table depth, depth of soil freezing and thawing, soil water storage in two layers, daily surface and total runoff from the catchment, and monthly evaporation from the catchment are validated against observations on a long-term basis. The root-mean-square errors (RMSEs) of simulations of soil water storage in the layers of 0,50 cm and 0,100 cm are equal to 16 mm and 24 mm respectively; the relative RMSE of simulated annual total runoff is 16%; the RMSE of daily snow surface temperature is 2·9 °C (the temperature varies from 0 to ,46 °C); the RMSE of maximum snow water equivalent (whose value averaged over 18 years is equal to 147 mm) is 32 mm. Analysis of the results of validation shows that the new version of the model SWAP reproduces the heat and water exchange processes occurring in mid-latitude boreal grassland reasonably well. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Brackish water subirrigation for vegetables,

    IRRIGATION AND DRAINAGE, Issue 2 2003
    R. M. Patel
    eaux saumâtres; irrigation souterraine; poivron vert; pommes de terre Abstract As freshwater resources for irrigation are being depleted rapidly, recent emphasis has been on the development of nonconventional water sources: reuse of agricultural drainage water, use of industrial or municipal wastewater, and use of brackish water for irrigation. Experiments conducted in field lysimeters over three seasons sought to investigate the feasibility of using brackish water for growing moderately sensitive crops. Brackish waters, with salinity levels of 1, 5 and 9 dS m,1, were used. In 1993 the effects of a factorial combination of three subirrigation water salinity levels, two water table depths and four NPK fertilizer combinations on salt buildup in an initially nonsaline soil and on green pepper (Capsicum annuum L.) performance were assessed. A gradual increase in soil solution salinity (ECsw) from the water table to the soil surface was evident; however, throughout the growing season, the ECsw did not reach a level that could seriously damage the crop. There was no significant difference in pepper yields due to either salinity of subirrigation water or water table depth. In 1994, two potato (Solanum tuberosum L.) cultivars were grown in the soil, which was salinized with 3.5 dS m,1 water before planting tubers. The salt buildup pattern was similar to that observed in 1993; however, the ECsw levels were higher in 1994 due to the higher initial soil salinity. Moreover, a decrease in ECsw was observed near the water table in lysimeters subirrigated with 1 dS m,1 water. For both cultivars, no significant difference in tuber yield was observed due to either water table depth or subirrigation water salinity. In 1995, three potato cultivars were grown in a nonsaline soil as well as a soil presalinized with 2 dS m,1 water. In the topsoil layer, higher rate of increase in ECsw was observed in the saline soil compared to the nonsaline soil. No significant difference in total tuber yield was observed due to either the initial soil salinity levels or subirrigation water salinity levels. Brackish water with salinity levels of up to 9 dS m,1, when applied through subirrigation, could be used to successfully produce green peppers and potatoes under semiarid to arid conditions. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Comme les ressources en eau douce utilisées poor l'irrigation s'épuisent rapidement, les récentes recherches tentent de mettre l'emphase sur le développement de sources d'eau non-conventionnelles: la réutilisation de l'eau de drainage agricole, l'utilisation des eaux usées municipales et des eaux saumâtres pour l'irrigation des cultures. Lors de pénuries d'eau douce les eaux saumâtres ont été utilisées pour l'irrigation souterraine de maïs, mais la salinité de la couche supérieur du sol a été réduite en raison de la pluie. Dans les régions arides et semi-arides cette méthode s'est limitée à quelques essais seulement. En raison des quantités limitées d'eau de bonne qualité, on ne peut irriguer de vastes étendues agricoles en régions arides. Or, si l'utilisation des eaux saumâtres s'avérait un succès il serait possible d'améliorer les rendements agricoles. Il est donc nécessaire d'évaluer l'utilisation des eaux saumâtres dans les systèmes d'irrigation souterrains en milieu aride. Des expériences en lysimètres au cours de trois saisons, dans le but d'étudier la faisabilité d'utiliser des eaux saumâtres pour l'irrigation souterraine de cultures moyennement sensibles, furent entreprises en 1993 et 1994. Des eaux saumâtres avec des niveaux de salinité de 1, 5 et 9 dS m,1, furent utilisés. En 1993, les effets d'une combinaison factorielle de trois niveaux de salinité, deux profondeurs de nappe phréatique et quatre combinaisons de fertilisation NPK ont servi à évaluer l'accumulation de sel dans un sol initialement non-salin où le poivron vert (Capsicum annuum L.) a été cultivé. Une augmentation graduelle de la salinité de la solution du sol, de la nappe d'eau souterraine jusqu'à la surface, fut évidente. Bien que durant la saison de croissance, la conductivité électrique de la solution du sol (ECsw) n'ait pas atteint un niveau qui aurait pu endommager sérieusement la culture. Ni les différents niveaux de salinité ni la profondeur de la nappe d'eau souterraine n'ont affecté de façon significative les rendements de poivrons. En 1994, deux cultivars de pommes de terre (Solanum tuberosum L.) furent cultivés dans un sol rendu salin, après avoir été irrigué avec une eau d'un niveau de salinité de 3.5 dS m,1, préalablement à la plantation des tubercules. L'accumulation de sel suivit une tendance semblable à celle observée en 1993. Cependant, les niveaux de ECsw enregistrés en 1994 furent plus élevés en raison du taux de salinité initial plus élevé. De plus, une baisse de ECsw fut observée près de la nappe d'eau souterraine dans les lysimètres irrigués avec une eau d'un niveau de salinité de 1 dS m,1. Ni les différents niveaux de salinité ni la profondeur de la nappe d'eau souterraine n'ont affecté de façon significative le rendement de pommes de terre de chacun des cultivars. En 1995, trois cultivars de pommes de terre ont été cultivés dans un soil non salin ainsi que dans un sol rendu salin au moyen d'une eau avec une conductivité électrique de 2 dS m,1. Dans la couche supérieure du sol, un plus important taux d'augmentation de conductivité électrique a été observé dans le sol salin que dans le sol non salin. Il n'y a pas eu de différence significative observée en raison des taux initiaux de salinité ou encore en raison des taux de salinité de l'eau dans le système d'irrigation souterrain. Cette étude suggère que les eaux saumâtres d'un niveau de salinité jusqu'à 9 dS m,1 pourraient être utilisées dans les systèmes d'irrigation souterrains pour la culture du poivron vert et de la pomme de terre en régions semi-arides et arides. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Evaluation of DRAINMOD-S for simulating water table management under semi-arid conditions,

    IRRIGATION AND DRAINAGE, Issue 3 2002
    M. A. S. Wahba
    modèl e dela direction dela table d'eau souterraine; le drainage conventionnel; le drainage contrôlé Abstract The water table management simulation model, DRAINMOD-S, was evaluated under semi-arid conditions using field data from the Maruit experimental field in the western delta of Egypt for three cropping seasons; maize 1999, wheat 1999/2000 and maize 2000. Two water table management systems (conventional drainage (FD) and controlled drainage (CD)) were applied in the study area. The recorded data included daily ground water table depths, drain outflows during flow events, soil salinity to depth of 1.20 m from the soil surface (0.30 m interval), and relative crop yield. DRAINMOD-S was run to simulate the applied water table management systems for the same study periods. The reliability of the model was evaluated by comparing measured and predicted values of the daily ground water table depth, cumulative outflow based on total monthly outflow, soil salinity during each season, and relative crop yield. Good agreement was found between the measured and predicted values. DRAINMOD-S predicted values within an absolute deviation ranged from 11.0 to 16.0 cm for ground water table depth, from 18 to 75 mm for drain outflows, from 0.22 to 1.08 dS m,1 for soil salinity, and from 4.62 to 4.86% for relative crop yield. The model showed the potential for long-term simulation and planning of ground water table management systems under semi-arid conditions of the western delta of Egypt. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Le modèle DRAINMOD-S pour simuler la direction de la table d'eau sous des conditions demi-arides á été évalué en utilisant le data des champs experimentaux du Mariut delta denileouest d'Égypte pendant trois saisons agricoles: le maïs 1999, le blé 1999/2000 et le maïs 2000. Deux systèmes de direction de la table d'eau (drainage conventionnel (FD) et drainage contrôlé (CD)) ontété appliqués àla superficie de l'étude. Le data qui s'est remis en ordre s'inclut les mesures des profondeurs de la table d'eau souterraine, les écoulements des drains pendant les évènements de l'écoulement, la salinité du sol au profondeur de 1.20 m souterrain aux intervalles de 30 cm, etles produits agricoles relatifs. DRAINMOD-S S'est mis en courant pour simuler l'application des systèmes de la direction pour la même période d'étude. La véracité du modèle aété évaluée en comparant les valeurs mésurées avec lcelles des produits agricoles sur le profondeur de la table d'eau quotidien, l'écoulement cumulatif basé sur l'écoulement total du mois, la salinité du sol pendant chaque saison, et les produits agricoles relatifs. On a trouvé un bon accord entre les valeurs mésurées et celles qu'on avait prédites avec une déviation absolue qui rangeait de 11.0 à 16.0 cm pour la profondeur de la table d'eau, de 18 à 75 mm pour l'écoulement du drains, et de 0.22 à 1.08 dS m,1, pour la salinité du sol et de 4.62 à 4.86% pour les produits agricoles relatifs. Le modèle a indiqué une éfficacité pour une simulation allongée et pour projeter les systèmes de la direction dela table d'eau souterraine auprès les conditions demi-arides du delta ouest en Egypte. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Sensitivity of Stream flow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed,

    JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010
    Zhaohua Dai
    Dai, Zhaohua, Carl C. Trettin, Changsheng Li, Devendra M. Amatya, Ge Sun, and Harbin Li, 2010. Sensitivity of Streamflow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed. Journal of the American Water Resources Association (JAWRA) 1,13. DOI: 10.1111/j.1752-1688.2010.00474.x Abstract:, A physically based distributed hydrological model, MIKE SHE, was used to evaluate the effects of altered temperature and precipitation regimes on the streamflow and water table in a forested watershed on the southeastern Atlantic coastal plain. The model calibration and validation against both streamflow and water table depth showed that the MIKE SHE was applicable for predicting the streamflow and water table dynamics for this watershed with an acceptable model efficiency (E > 0.5 for daily streamflow and >0.75 for monthly streamflow). The simulation results from changing temperature and precipitation scenarios indicate that climate change influences both streamflow and water table in the forested watershed. Compared to current climate conditions, the annual average streamflow increased or decreased by 2.4% with one percentage increase or decrease in precipitation; a quadratic polynomial relationship between changes in water table depth (cm) and precipitation (%) was found. The annual average water table depth and annual average streamflow linearly decreased with an increase in temperature within the range of temperature change scenarios (0-6°C). The simulation results from the potential climate change scenarios indicate that future climate change will substantially impact the hydrological regime of upland and wetland forests on the coastal plain with corresponding implications to altered ecosystem functions that are dependent on water. [source]

    EFFECTS OF CONTROLLED DRAINAGE ON STORM EVENT HYDROLOGY IN A LOBLOLLY PINE PLANTATION,

    JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2000
    D. M. Amatya
    ABSTRACT: A paired watershed approach was utilized to study the effects of three water management regimes on storm event hydrology in three experimental watersheds in a drained loblolly pine (Pinus taeda L.) plantation in eastern North Carolina. The regimes were: (1) conventional drainage, (2) controlled drainage (CD) to reduce outflows during spring fish recruitment, and (3) controlled drainage to reduce outflows and conserve water during the growing season. Data from two pit-treatment years and three years of CD treatment with raised weirs at the watershed outlet are presented. CD treatment resulted in rises in water table elevations during the summer. But the rises were small and short-lived due to increased evapotranspiration (ET) rates as compared to the spring treatment with lower ET demands. CD treatment had no effect on water tables deeper than 1.3 m. CD treatments, however, significantly (,= 0.05) reduced the stoning outflows for all events, and peak outflow rates for most of the events depending upon the outlet weir level. In some events, flows did not occur at all in watersheds with CD. When event outflows occurred, duration of the event was sharply reduced because of reduced effective ditch depth. Water table depth at the start of an event influenced the effect of CD treatment on storm event hydrology. [source]

    Salt Marsh Restoration in Connecticut: 20 Years of Science and Management

    RESTORATION ECOLOGY, Issue 3 2002
    R. Scott Warren
    Abstract In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass (Phragmites australis) and cattail (Typha angustifolia and T. latifolia), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., pre-disturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established on a slow-recovery marsh, reed grass dominated after 9 years. Typical fish species assemblages were found in restoration site creeks and ditches within 5 years. Gut contents of fish in ditches and on the high marsh suggest that use of restored marsh as foraging areas may require up to 15 years to reach equivalence with reference sites. Bird species that specialize in salt marshes require appropriate vegetation; on the oldest restoration site, breeding populations comparable with reference marshland had become established after 15 years. Use of restoration sites by birds considered marsh generalists was initially high and was still nearly twice that of reference areas even after 20 years. Herons, egrets, and migratory shorebirds used restoration areas extensively. These results support our prediction that returning tides will set degraded marshes on trajectories that can bring essentially full restoration of ecological functions. This can occur within two decades, although reduced tidal action can delay restoration of some functions. With this success, Connecticut's Department of Environmental Protection established a dedicated Wetland Restoration Unit. As of 1999 tides have been restored at 57 separate sites along the Connecticut coast. [source]

    Modelling variable source area dynamics in a CEAP watershed

    ECOHYDROLOGY, Issue 3 2009
    Helen E. Dahlke
    Abstract In the Northeast US, saturation excess is the most dominant runoff process and locations of runoff source areas, typically called variable source areas (VSAs), are determined by the available soil water storage and the landscape topographic position. To predict runoff generated from VSAs some water quality models use the Soil Conservation Service Curve Number equation (SCS-CN), which assumes a constant initial abstraction of rainfall is retained by the watershed prior to the beginning of runoff. We apply a VSA interpretation of the SCS-CN runoff equation that allows the initial abstraction to vary with antecedent moisture conditions. We couple this modified SCS-CN approach with a semi-distributed water balance model to predict runoff, and distribute predictions using a soil topographic index for the Town Brook watershed in the Catskill Mountains of New York State. The accuracy of predicted VSA extents using both the original and the modified SCS-CN equation were evaluated for 14 rainfall-runoff events through a comparison with average water table depths measured at 33 locations in Town Brook from March,September 2004. The modified SCS-CN equation captured VSA dynamics more accurately than the original equation. However, during events with high antecedent rainfall VSA dynamics were still under-predicted suggesting that VSA runoff is not captured solely by knowledge of the soil water deficit. Considering the importance of correctly predicting runoff generation and pollutant source areas in the landscape, the results of this study demonstrate the feasibility of integrating VSA hydrology into water quality models to reduce non-point source pollution. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Brackish water subirrigation for vegetables,

    IRRIGATION AND DRAINAGE, Issue 2 2003
    R. M. Patel
    eaux saumâtres; irrigation souterraine; poivron vert; pommes de terre Abstract As freshwater resources for irrigation are being depleted rapidly, recent emphasis has been on the development of nonconventional water sources: reuse of agricultural drainage water, use of industrial or municipal wastewater, and use of brackish water for irrigation. Experiments conducted in field lysimeters over three seasons sought to investigate the feasibility of using brackish water for growing moderately sensitive crops. Brackish waters, with salinity levels of 1, 5 and 9 dS m,1, were used. In 1993 the effects of a factorial combination of three subirrigation water salinity levels, two water table depths and four NPK fertilizer combinations on salt buildup in an initially nonsaline soil and on green pepper (Capsicum annuum L.) performance were assessed. A gradual increase in soil solution salinity (ECsw) from the water table to the soil surface was evident; however, throughout the growing season, the ECsw did not reach a level that could seriously damage the crop. There was no significant difference in pepper yields due to either salinity of subirrigation water or water table depth. In 1994, two potato (Solanum tuberosum L.) cultivars were grown in the soil, which was salinized with 3.5 dS m,1 water before planting tubers. The salt buildup pattern was similar to that observed in 1993; however, the ECsw levels were higher in 1994 due to the higher initial soil salinity. Moreover, a decrease in ECsw was observed near the water table in lysimeters subirrigated with 1 dS m,1 water. For both cultivars, no significant difference in tuber yield was observed due to either water table depth or subirrigation water salinity. In 1995, three potato cultivars were grown in a nonsaline soil as well as a soil presalinized with 2 dS m,1 water. In the topsoil layer, higher rate of increase in ECsw was observed in the saline soil compared to the nonsaline soil. No significant difference in total tuber yield was observed due to either the initial soil salinity levels or subirrigation water salinity levels. Brackish water with salinity levels of up to 9 dS m,1, when applied through subirrigation, could be used to successfully produce green peppers and potatoes under semiarid to arid conditions. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Comme les ressources en eau douce utilisées poor l'irrigation s'épuisent rapidement, les récentes recherches tentent de mettre l'emphase sur le développement de sources d'eau non-conventionnelles: la réutilisation de l'eau de drainage agricole, l'utilisation des eaux usées municipales et des eaux saumâtres pour l'irrigation des cultures. Lors de pénuries d'eau douce les eaux saumâtres ont été utilisées pour l'irrigation souterraine de maïs, mais la salinité de la couche supérieur du sol a été réduite en raison de la pluie. Dans les régions arides et semi-arides cette méthode s'est limitée à quelques essais seulement. En raison des quantités limitées d'eau de bonne qualité, on ne peut irriguer de vastes étendues agricoles en régions arides. Or, si l'utilisation des eaux saumâtres s'avérait un succès il serait possible d'améliorer les rendements agricoles. Il est donc nécessaire d'évaluer l'utilisation des eaux saumâtres dans les systèmes d'irrigation souterrains en milieu aride. Des expériences en lysimètres au cours de trois saisons, dans le but d'étudier la faisabilité d'utiliser des eaux saumâtres pour l'irrigation souterraine de cultures moyennement sensibles, furent entreprises en 1993 et 1994. Des eaux saumâtres avec des niveaux de salinité de 1, 5 et 9 dS m,1, furent utilisés. En 1993, les effets d'une combinaison factorielle de trois niveaux de salinité, deux profondeurs de nappe phréatique et quatre combinaisons de fertilisation NPK ont servi à évaluer l'accumulation de sel dans un sol initialement non-salin où le poivron vert (Capsicum annuum L.) a été cultivé. Une augmentation graduelle de la salinité de la solution du sol, de la nappe d'eau souterraine jusqu'à la surface, fut évidente. Bien que durant la saison de croissance, la conductivité électrique de la solution du sol (ECsw) n'ait pas atteint un niveau qui aurait pu endommager sérieusement la culture. Ni les différents niveaux de salinité ni la profondeur de la nappe d'eau souterraine n'ont affecté de façon significative les rendements de poivrons. En 1994, deux cultivars de pommes de terre (Solanum tuberosum L.) furent cultivés dans un sol rendu salin, après avoir été irrigué avec une eau d'un niveau de salinité de 3.5 dS m,1, préalablement à la plantation des tubercules. L'accumulation de sel suivit une tendance semblable à celle observée en 1993. Cependant, les niveaux de ECsw enregistrés en 1994 furent plus élevés en raison du taux de salinité initial plus élevé. De plus, une baisse de ECsw fut observée près de la nappe d'eau souterraine dans les lysimètres irrigués avec une eau d'un niveau de salinité de 1 dS m,1. Ni les différents niveaux de salinité ni la profondeur de la nappe d'eau souterraine n'ont affecté de façon significative le rendement de pommes de terre de chacun des cultivars. En 1995, trois cultivars de pommes de terre ont été cultivés dans un soil non salin ainsi que dans un sol rendu salin au moyen d'une eau avec une conductivité électrique de 2 dS m,1. Dans la couche supérieure du sol, un plus important taux d'augmentation de conductivité électrique a été observé dans le sol salin que dans le sol non salin. Il n'y a pas eu de différence significative observée en raison des taux initiaux de salinité ou encore en raison des taux de salinité de l'eau dans le système d'irrigation souterrain. Cette étude suggère que les eaux saumâtres d'un niveau de salinité jusqu'à 9 dS m,1 pourraient être utilisées dans les systèmes d'irrigation souterrains pour la culture du poivron vert et de la pomme de terre en régions semi-arides et arides. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Evaluation of DRAINMOD-S for simulating water table management under semi-arid conditions,

    IRRIGATION AND DRAINAGE, Issue 3 2002
    M. A. S. Wahba
    modèl e dela direction dela table d'eau souterraine; le drainage conventionnel; le drainage contrôlé Abstract The water table management simulation model, DRAINMOD-S, was evaluated under semi-arid conditions using field data from the Maruit experimental field in the western delta of Egypt for three cropping seasons; maize 1999, wheat 1999/2000 and maize 2000. Two water table management systems (conventional drainage (FD) and controlled drainage (CD)) were applied in the study area. The recorded data included daily ground water table depths, drain outflows during flow events, soil salinity to depth of 1.20 m from the soil surface (0.30 m interval), and relative crop yield. DRAINMOD-S was run to simulate the applied water table management systems for the same study periods. The reliability of the model was evaluated by comparing measured and predicted values of the daily ground water table depth, cumulative outflow based on total monthly outflow, soil salinity during each season, and relative crop yield. Good agreement was found between the measured and predicted values. DRAINMOD-S predicted values within an absolute deviation ranged from 11.0 to 16.0 cm for ground water table depth, from 18 to 75 mm for drain outflows, from 0.22 to 1.08 dS m,1 for soil salinity, and from 4.62 to 4.86% for relative crop yield. The model showed the potential for long-term simulation and planning of ground water table management systems under semi-arid conditions of the western delta of Egypt. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Le modèle DRAINMOD-S pour simuler la direction de la table d'eau sous des conditions demi-arides á été évalué en utilisant le data des champs experimentaux du Mariut delta denileouest d'Égypte pendant trois saisons agricoles: le maïs 1999, le blé 1999/2000 et le maïs 2000. Deux systèmes de direction de la table d'eau (drainage conventionnel (FD) et drainage contrôlé (CD)) ontété appliqués àla superficie de l'étude. Le data qui s'est remis en ordre s'inclut les mesures des profondeurs de la table d'eau souterraine, les écoulements des drains pendant les évènements de l'écoulement, la salinité du sol au profondeur de 1.20 m souterrain aux intervalles de 30 cm, etles produits agricoles relatifs. DRAINMOD-S S'est mis en courant pour simuler l'application des systèmes de la direction pour la même période d'étude. La véracité du modèle aété évaluée en comparant les valeurs mésurées avec lcelles des produits agricoles sur le profondeur de la table d'eau quotidien, l'écoulement cumulatif basé sur l'écoulement total du mois, la salinité du sol pendant chaque saison, et les produits agricoles relatifs. On a trouvé un bon accord entre les valeurs mésurées et celles qu'on avait prédites avec une déviation absolue qui rangeait de 11.0 à 16.0 cm pour la profondeur de la table d'eau, de 18 à 75 mm pour l'écoulement du drains, et de 0.22 à 1.08 dS m,1, pour la salinité du sol et de 4.62 à 4.86% pour les produits agricoles relatifs. Le modèle a indiqué une éfficacité pour une simulation allongée et pour projeter les systèmes de la direction dela table d'eau souterraine auprès les conditions demi-arides du delta ouest en Egypte. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Modern Sphagnum,13C signatures follow a surface moisture gradient in two boreal peat bogs, James Bay lowlands, Québec,

    JOURNAL OF QUATERNARY SCIENCE, Issue 3 2009
    Julie Loisel
    Abstract Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat-based climatic studies since a relationship between Sphagnum ,13C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum,13C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P,<,0.0001) was found between Sphagnum,13C values and their position along the surface moisture gradient. Results show that 13C-depleted values are related to low water table depths (WTD), while 13C-enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO2 diffusion is an important fractionation process that is observed in bulk Sphagnum,13C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd. [source]