Water Control Structures Research Articles

A Suggested Module for Risk Framework of Water Control Construction Projects using Qualitative and Quantitative Techniques

Managing risk is an integral part of sound management and risk management helps to achieve projects objectives. Although the process of risk management is standardized to a great extent, risk control strategies depend on project circumstances and feature. One of the essential humanity’s challenges in the future, is surely ensuring water needs. Equitable and sustainable management of water resources is a major global challenge, and supply of clean fresh water is decreasing around all nations. Egypt is one of the countries hardest affected by climate change. Also challenges include population growth, increase in food demand and Lack of water and energy Leads to let managing risk for construction of water control structures projects on water streams in Egypt becomes more challenging and essential than ever before. Moreover, this study aims to show the effect of risk on cost and time targets for water control structure projects in Egypt .This study mainly identify a list of significant risk factors effecting on cost and time for these type of projects in Egypt through studying pervious publishing for risk management in construction projects and a questionnaire survey , then conducting a qualitative analysis using a Severity and Probability matrix (S/P matrix) techniques to assess the influence of risk factors and to isolate critical risk factors for a quantitative analysis. Finally, conducting a quantitative analysis by mean of Analytical Hierarchy Process (AHP) to determine the cost and time contingency, s the conclusion of this study shows that the cost contingency needed to account for the different critical risk factors is to increase the estimated cost by 12.35 % on the total estimated budget of the project. In addition that the time contingency needed to consider for different critical risk factors is to increase the scheduled time by 11.25% over the total originally scheduled of the project.

Ice in reservoirs and regulated rivers

ABSTRACT In a river with seasonal ice covers, river ice effects must be considered in the design and operation of water control structures such as dams, barrages, and spillways. The regulation of flow and the water levels of rivers and reservoirs have several hydrological, socio-economic, and ecological effects. Regulation alters river-ice regimes by modifying the temporal and spatial characteristics of flow, water level, and thermal regimes in a watercourse. Removal of a water control structure and reservoir can eliminate some problems, but create new problems in areas where environmental or development conditions have changed. Therefore, thorough review of proposals to regulate (or remove regulation on) a river with seasonal ice covers is necessary. The effects of regulation on ice conditions and vice-versa are reviewed in this paper. Although considerable progress has been made during recent years, adequate understanding of the effects of river-ice interaction with structures and the effect of regulation on geomorphology, people, and aquatic habitat requires additional research.

Managing New Risks of and Opportunities for the Agricultural Development of West-African Floodplains: Hydroclimatic Conditions and Implications for Rice Production

High rainfall events and flash flooding are becoming more frequent, leading to severe damage to crop production and water infrastructure in Burkina Faso, Western Africa. Special attention must therefore be given to the design of water control structures to ensure their flexibility and sustainability in discharging floods, while avoiding overdrainage during dry spells. This study assesses the hydroclimatic risks and implications of floodplain climate-smart rice production in southwestern Burkina Faso in order to make informed decisions regarding floodplain development. Statistical methods (Mann-Kendall test, Sen’s slope estimator, and frequency analysis) combined with rainfall-–runoff modeling (HBV model) were used to analyze the hydroclimatic conditions of the study area. Moreover, the spatial and temporal water availability for crop growth was assessed for an innovative and participatory water management technique. From 1970 to 2013, an increasing delay in the onset of the rainy season (with a decreasing pre-humid season duration) occurred, causing difficulties in predicting the onset due to the high temporal variability of rainfall in the studied region. As a result, a warming trend was observed for the past 40 years, raising questions about its negative impact on very intensive rice cultivation packages. Farmers have both positive and negative consensual perceptions of climatic hazards. The analysis of the hydrological condition of the basin through the successfully calibrated and validated hydrological HBV model indicated no significant increase in water discharge. The sowing of rice from the 10th to 30th June has been identified as optimal in order to benefit from higher surface water flows, which can be used to irrigate and meet crop water requirements during the critical flowering and grain filling phases of rice growth. Furthermore, the installation of cofferdams to increase water levels would be potentially beneficial, subject to them not hindering channel drainage during peak flow.

The isotope hydrology of the Muskoka River Watershed, Ontario, Canada

AbstractStable isotope tracers of δ18O and δ2H are increasingly being applied in the study of water cycling in regional‐scale watersheds in which human activities, like river regulation, are important influences. In 2015, δ18O and δ2H were integrated into a water quality survey in the Muskoka River Watershed with the aim to provide new regional‐scale characterization of isotope hydrology in the 5,100‐km2 watershed located on the Canadian Shield in central Ontario, Canada. The forest dominated region includes ~78,000 ha of lakes, 42 water control structures, and 11 generating stations, categorized as “run of river.” Within the watershed, stable isotope tracers have long been integrated into hydrologic process studies of both headwater catchments and lakes. Here, monthly surveys of δ18O and δ2H in river flow were conducted in the watershed between April 2015 and November 2016 (173 surface water samples from 10 river stations). Temporal patterns of stable isotopes in river water reflect seasonal influences of snowmelt and summer‐time evaporative fractionation. Spatial patterns, including differences observed during extreme flood levels experienced in the spring of 2016, reflect variation in source contributions to river flow (e.g., snowmelt or groundwater versus evaporatively enriched lake storage), suggesting more local influences (e.g., glacial outwash deposits). Evidence of combined influences of source mixing and evaporative fractionation could, in future, support application of tracer‐enabled hydrological modelling, estimation of mean transit times and, as such, contribute to studies of water quality and water resources in the region.

Transformation of maritime desert to an agricultural center: Holocene environmental change and landscape engineering in Chicama River valley, northern Peru coast

Some of the earliest Andean populations settled in the region's arid coastal river valleys, supported by abundant marine life despite having domesticated plant cultigens as early as ∼10 ka. In the Chicama River valley, this maritime economy dominated at the Preceramic site, Huaca Prieta, until ∼6 ka, after which agricultural production began to increase significantly. This agricultural expansion was motivated in part by the development of arable fine-grained soils along the coast as the result of slowing sea-level rise, enhanced river floods, and unique basin lithology. Local populations made use of the stabilized floodplain and wetland settings to conduct raised-terrace farming. By ∼3.5 ka, growth in agriculture and the new fine-grained sediment resources led to several major cultural developments, including the production of fired-ceramic pottery and adobe-brick monument construction associated with the Cupisnique culture. Populations thereafter expanded into the middle valley, where the Salinar and Gallinazo cultures used small water-control structures to farm local ravines. These cultural and technological developments all parallel natural environmental changes driven by increasing ENSO-related water and sediment discharge. By ∼1.8 ka, though, further expansion of agriculture –and arable land– was driven primarily by direct human manipulation of the environment. The construction of an ever-expanding network of irrigation canals diverted increasing volumes of water and sediment to distal reaches of the Chicama valley, supporting the great Moche and Chimu civilizations, and persisting through the Inka and Colonial periods. This history of Chicama valley traces strongly coupled interactions between the human and natural environments, supporting significant socio-cultural, economic, demographic, and technological advances.

From free to forced adaptation: A political ecology of the ‘state‐society‐flood’ nexus in the Vietnamese Mekong Delta

This paper investigates the adaptation processes with reference to the narrative analysis of human–environment interactions in the Vietnamese Mekong Delta. From the political ecology perspective, it focuses on the discourses of the power relationships embedded within the ‘state‐society‐flood’ nexus over the course of its ‘opening‐up and closing‐off’ processes (e.g. excavating large‐scale canals for human settlements and agricultural expansion (opening‐up) and human interventions into natural systems through water control structures (closing‐off)). Drawing on empirical data gathered from 33 interviews and nine focus group discussions in three study areas and relevant literature, the paper argues that human interactions with the flood environments are intertwined with adjustments of adaptation patterns as evidenced through three periods: free adaptation (pre‐1975), transitional adaptation (1976–2010) and forced adaptation (after 2010). These processes have witnessed a gradual power shift in the ‘state‐society’ relations in manipulating floods, which moves from the top‐down towards a more collaborative fashion. By unravelling the political ecology of the ‘state‐society‐flood’ nexus, this paper exhibits the skewed development in the delta, which is largely bound to short‐term development planning to prioritise local socio‐economic and political objectives. The paper contributes important policy implications for achieving socially just and environmentally sustainable development in the delta.

Shifting Ground: Landscape-Scale Modeling of Biogeochemical Processes under Climate Change in the Florida Everglades.

Scenarios modeling can be a useful tool to plan for climate change. In this study, we help Everglades restoration planning to bolster climate change resiliency by simulating plausible ecosystem responses to three climate change scenarios: a Baseline scenario of 2010 climate, and two scenarios that both included 1.5 °C warming and 7% increase in evapotranspiration, and differed only by rainfall: either increase or decrease by 10%. In conjunction with output from a water-use management model, we used these scenarios to drive the Everglades Landscape Model to simulate changes in a suite of parameters that include both hydrologic drivers and changes to soil pattern and process. In this paper we focus on the freshwater wetlands; sea level rise is specifically addressed in prior work. The decreased rainfall scenario produced marked changes across the system in comparison to the Baseline scenario. Most notably, muck fire risk was elevated for 49% of the period of simulation in one of the three indicator regions. Surface water flow velocity slowed drastically across most of the system, which may impair soil processes related to maintaining landscape patterning. Due to lower flow volumes, this scenario produced decreases in parameters related to flow-loading, such as phosphorus accumulation in the soil, and methylmercury production risk. The increased rainfall scenario was hydrologically similar to the Baseline scenario due to existing water management rules. A key change was phosphorus accumulation in the soil, an effect of flow-loading due to higher inflow from water control structures in this scenario.

A Numerical Simulation for the Determination of the Shunt Ratio at a T-Junction With Different Branch Angles, Viscosities, and Flow Rates

T-junctions have been applied in water-control structures. A comprehensive understanding of shunt characteristics can contribute to the optimal design of T-junctions. In this work, we seek to understand the shunt ratio of fluids with different viscosities in a T-junction and to achieve a greater shunt ratio. The computational fluid dynamics (CFD) approach is applied to study the influence of the properties, such as the fluid viscosity, the branch angle, the channel shape, and the flow rate, on the shunt ratio in a T-junction. The viscosity of oil can be divided into three intervals, and the optimal angles of the T-junction are different in each interval. For the fluid viscosity in the 1–20 cP range, the optimal branch angle is in the 45–60 deg range. For the fluid viscosity in the 20–65 cP range, the branch angle should be designed to be 45 deg. For the viscosity greater than 65 cP, the branch angle should be designed to be 75 deg. The appearance of the eddy and secondary flow will reduce the flow. The secondary flow and eddy intensity on the branch increase with increasing angle. The secondary flow intensity of the main channel decreases gradually with the increase in the angle. This study provides an important guidance for the design of automatic water control valve tools.

Evaluation of Soil Conservation Structures in Sloppy Lands of Sohawa Area for Soil Moisture and Fertility Conservation

Pothohar region of the Punjab, Pakistan is rain-fed with undulating topography. Soils of the area are predominantly loose with low water retention capacity and are vulnerable to erosion. Erratic and high intensity rainfall causes land erosion in the area producing gullies and gorges. Therefore, agriculture in the area faces twin menace of soil erosion and moisture stress. On-farm water control structures are among the important measures to control soil erosion and conserve moisture to enhance agriculture productivity. Present study was designed to evaluate the impact of these structures on soil moisture conservation and physio-chemical characteristics of soil in wheat growing fields. Wheat was sown in the fields, with and without structures during 2009 to 2013. It has been found that construction cost of such structures is about one-fourth that of conventionally used structures in the area whereas reduction in soil erosion has been observed up to 10% with 21% soil moisture conservation as compared to control. Soil fertility level improved significantly as a result of reduced run off and nutrient loss. A substantial improvement in wheat yield up to 15% due to increased fertility and moisture content was also recorded. These structures facilitated a safe disposal of surplus rain water which minimized the gully development, improved the soil structure, checked fertility loss and improved soil moisture retention.

Hydrodynamic Modeling Improves Green River Reconnection with Floodplain Wetlands for Endangered Fish Species Recovery

AbstractWe performed two‐dimensional (2D) hydrodynamic modeling to aid recovery of the endangered razorback sucker (Xyrauchen texanus) by reconnecting the Green River with its historic bottomland floodplain wetlands at Ouray National Wildlife Refuge, Utah. Reconnection allows spring flood flows to overtop the river levee every two to three years, and passively transport razorback sucker larvae to the wetlands to grow in critical habitat. This study includes (1) river hydrologic analysis, (2) simulation of a levee breach/weir, overtopping of river flood flows, and 2D flow through the wetlands using Hydrologic Engineering Center River Analysis System 2D, and (3) modeling flow and restoration scenarios. Indicators of hydrologic alteration were used to evaluate river flow metrics, in particular flood magnitudes, frequency, and duration. Results showed a target spring flow of 16,000 cfs (453 m3/s) and a levee breach elevation of 4,663 ft (1,421 m) amsl would result in a median flow >6,000 acre‐feet (7.4 million m3) over five days into the wetlands, which is adequate for razorback sucker larvae transport and rearing. Modeling of flow/restoration scenarios showed using gated water control structures and passive low‐water crossings between wetland units can provide adequate control of flow movement into and storage in multiple units. Levee breaching can be a relatively simple, cost‐effective method to reconnect rivers and historic floodplains, and hydrodynamic modeling is an important tool for analyzing and designing wetland reconnection.

Linking ecosystem function and hydrologic regime to inform restoration of a forested peatland

Drainage is a globally common disturbance in forested peatlands that impacts peat soils, forest communities, and associated ecosystem functions, calling for informed hydrologic restoration strategies. The Great Dismal Swamp (GDS), located in Virginia and North Carolina, U.S.A., has been altered since colonial times, particularly by extensive ditch networks installed to lower water levels and facilitate timber harvests. Consequently, peat decomposition rates have accelerated, and red maple has become the dominant tree species, reducing the historical mosaic of bald cypress, Atlantic white-cedar, and pocosin stands. Recent repair and installation of water control structures aim to control drainage and, in doing so, enhance forest community composition and preserve peat depths. To help inform these actions, we established five transects of 15 plots each (75 plots total) along a hydrologic gradient where we measured continuous water levels and ecosystem attributes, including peat depths, microtopography, and forest composition and structure. We found significant differences among transects, with wetter sites having thicker peat, lower red maple importance, greater tree density, and higher overall stand richness. Plot-level analyses comported with these trends, clearly grouping plots by transects (via nonmetric multidimensional scaling) and resulting in significant correlations between specific hydrologic metrics and ecosystem attributes. Our findings highlight hydrologic controls on soil carbon storage, forest structure, and maple dominance, with implications for large-scale hydrologic restoration at GDS and in other degraded forested peatlands more broadly.

Pink shrimp Farfantepenaeus duorarum spatiotemporal abundance trends along an urban, subtropical shoreline slated for restoration.

The Biscayne Bay Coastal Wetlands (BBCW) project of the Comprehensive Everglades Restoration Plan (CERP) aims to reduce point-source freshwater discharges and spread freshwater flow along the mainland shoreline of southern Biscayne Bay. These actions will be taken to approximate conditions in the coastal wetlands and bay that existed prior to construction of canals and water control structures. An increase in pink shrimp (Farfantepenaeus duorarum) density to ≥ 2 individuals m-2 during the wet season (i.e., August-October) along the mainland shoreline was previously proposed as an indication of BBCW success. This study examined pre-BBCW baseline densities and compared them with the proposed target. Densities were monitored by seasonal (wet, dry) throw-trapping (1 m2 replicated in triplicate) at 47 sites along ~22 km of the southwestern Biscayne Bay coastline over 10 years (2007–2016). Densities varied across years and were most often higher in dry seasons. Quantile regression revealed density limitation by four habitat attributes: water temperature (°C), depth (m), salinity (ppt), and submerged aquatic vegetation (SAV: % cover). Procrustean analyses that tested for concordance between the spatial and temporal distributions of shrimp densities and habitat metrics found that water temperature, water depth, and salinity explained ~ 28%, 28%, and 22% of density variability, respectively. No significant relationship with SAV was observed. Hierarchical clustering was used to identify spatially and temporally similar groupings of pink shrimp densities by sites or season-years. Significant groupings were then investigated with respect to potentially limiting habitat attributes. Six site and four year-season clusters were identified. Although habitat attributes significantly differed among spatial clusters, within-cluster median pink shrimp densities did not correlate with within-cluster minima, maxima, medians, or standard deviations of habitat attributes. Overall, pink shrimp density ( = 0.86, SD = 1.32 shrimp m-2) was significantly lower (t(α = 0.10,2),939 = -26.53, P <0.0001) than the 2 shrimp m-2 CERP Interim Goal target. Pink shrimp density corresponded significantly with salinity and appeared limited to density < 2 shrimp m-2 by salinity < ~18 ppt. Salinity is an environmental attribute that will be directly influenced by CERP implementation.

Forestry best management practices and modeled erosion on planned and logger-selected bladed skid trails in the Ridge and Valley region, Virginia, USA

ABSTRACTForestry Best Management Practices (BMPs) are techniques and approaches recommended by state forestry agencies to protect water quality from forestry operations. Poorly designed roads and skid trails with inadequate BMPs can potentially generate disproportionately large quantities of sediment, which is the primary pollutant from forest operations. Bladed skid trails, which are constructed on steep terrain to allow skidder access, have greater potential to produce sediment than overland skid trails. BMP recommendations advise pre-harvest planning and layout of bladed skid trails in order to minimize erosion, yet equipment operators commonly construct bladed skid trails with minimal planning. We examined pre-harvest planned and logger-selected skid trails to characterize differences in BMP implementation and potential erosion between the two skid trail layout/construction strategies. A total of 25 and 27 sample locations on logger-selected and pre-harvest planned bladed skid trails were installed on two recent timber harvests on steep terrain in the Ridge and Valley region in Montgomery County, Virginia, USA. Both planned and logger-selected trails were on similar terrain and were constructed by the same logging crew. Assessments included skid trail slope, soil cover, water control structure implementation and spacing, trail network geometries, and predicted soil erosion. Analyses revealed that slopes, trail areas, and erosion rates were significantly lower on pre-harvest planned bladed skid trails. Overall, bladed skid trails with pre-harvest planning resulted in more effective water control BMPs and reduced potential for soil erosion than logger-selected trails. Results emphasize that pre-harvest planning of bladed skid trails is an appropriate BMP for steep terrain.

Assessing the success of hydrological restoration in two conservation easements within Central Florida ranchland.

In the USA, the United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS) has restored millions of acres of wetlands through its Wetland Reserve Easement (WRE) programs. However, few quantitative studies have explored whether WREs have enhanced wetland hydrology and wetland plant communities. Additionally, USDA Compatible Use Permits for cattle grazing and other management practices are sometimes issued for WREs, but little is known about potential benefits/detriments of such practice on the success of wetland restoration. In this study, we tested if hydrological restoration of previously drained species poor pastures increased water depth and hydroperiod. Restoration involved plugging key ditches, adding water control structures and a berm. We also tested if hydrological restoration increased plant diversity (alpha and beta), floristic quality (using coefficient of conservatism) and increased the cover of wetland species (using species wetland status). Finally, we tested if cattle grazing had an effect on the success of restoration by comparing grazed plots to fenced plots. We studied two conservation easements (a total of 748 acres) located on semi-native pastures in central Florida, USA. We monitored vegetation using permanent transects stratified by vegetation type before (2004–2005) and after (2012) the restoration (2008). We assessed wetland hydroperiod using groundwater wells set up in 2003 and located within and outside the boundaries of these two easements. We used linear mixed models and multivariate analyses to compare vegetation and hydroperiods pre- and post-restoration. Number of flooded days increased following restoration in one of the easements, but we did not detect significant changes in hydrology in the other easement. Floristic quality, beta diversity and cover of obligate wetland species increased in both conservation easements and in most vegetation types. These vegetation changes were likely due to restoration activities since annual rainfall was not significantly different pre- and post-restoration. Cattle grazing did not have a negative or positive effect on the success of restoration, nor did we detect any positive effect of grazing on the success of restoration. Overall, our study shows that hydrological restoration can enhance wetland hydroperiod, water depth and wetland vegetation, but more resources should be allocated to short- and long-term monitoring of the restoration success.

Changes in bird assemblages in a wetland ecosystem after 14 years of intensified cattle farming

AbstractHuman activities have modified wetlands all over the word. Water control structures that are frequently implemented in these ecosystems to keep lands free of flooding can decrease or degrade habitat for biodiversity. The Paraná River Delta, one of the largest wetlands in Argentina, has recently experienced rapid cattle grazing intensification facilitated by water control structures, resulting in extensive conversion of wetlands to pastures. It is unclear if this loss of wetlands has had a negative impact on the highly diverse bird community. Here, we evaluated the changes in bird assemblages in the Lower Delta of Paraná River after 14 years of cattle grazing intensification. We compared point count data from 1997 to 1999 with data collected in 2012 and 2013 using the same survey methods. We assessed the temporal changes in bird richness and composition using paired permutation tests and multivariate analysis. We related the bird composition to landscape changes to analyse if avian changes were associated with landscape dynamics. We found that after 14 years, the bird community differed greatly. In general, species richness decreased, especially in wet years. We found fewer wetland species in recent surveys; in particular we did not register saffron‐cowled blackbird (Xanthopsar flavus), a species listed as globally vulnerable. Changes in bird composition were associated with an increase in bare soil due to land‐use changes. Even though inter‐annual differences in precipitation and river stage have great effects on the species present in the surveys, the absence of many wetland species in recent wet years, that is when habitat is suitable for them, is most likely due to changes in land cover. Globally, agricultural land use makes inroads into many wetlands, eroding their quality and extent. Maintenance of wetland species requires that conservation efforts focus on these vulnerable ecosystems before full‐scale land conversion occurs.

Herpetofaunal Inventory of Wormsloe State Historic Site, Savannah, Georgia

There is renewed interest in inventory and monitoring projects, due in part to mandates to evaluate the effects of surrounding development and climate change on the biotic communities of public lands. We inventoried an understudied area, Wormsloe State Historic Site, near Savannah, GA. We directly observed or trapped 21 herpetofaunal (i.e., amphibian and reptile) species. Chao estimates predicted that <1 additional amphibian species and 3–4 additional reptile species might occur with further trapping. Most species had low abundance: <10 individuals for 75% of species. Species richness on Wormsloe was about ⅓ that recorded on the adjacent mainland (<1 km distance). Some species not detected required specific habitats lacking at Wormsloe. Other undetected species may have been extirpated by past land-uses. Also, the changing landscape context, caused by development of surrounding areas, has likely diminished both landscape connectivity and available freshwater, shortening the hydroperiod of breeding ponds. Of import to breeding amphibians, each of the depressions on Wormsloe has a drainage ditch connecting it to salt-water tides but the water-control structures preventing tidal flux are no longer in place. Resources management can improve amphibian breeding habitat simply by eliminating tidal influxes along drainage ditches. Maintaining existing populations of common species should be a priority for all public lands.

The geomorphic legacy of water and erosion control structures in a semiarid rangeland watershed

AbstractControl over water supply and distribution is critical for agriculture in drylands where manipulating surface runoff often serves the dual purpose of erosion control. However, little is known of the geomorphic impacts and legacy effects of rangeland water manipulation infrastructure, especially if not maintained. This study investigated the geomorphic impacts of structures such as earthen berms, water control gates, and stock tanks, in a semiarid rangeland in the southwestern USA that is responding to both regional channel incision that was initiated over a century ago, and a more recent land use change that involved cattle removal and abandonment of structures. The functional condition of remnant structures was inventoried, mapped, and assessed using aerial imagery and lidar data. Headcut initiation, scour, and channel incision associated with compromised lateral channel berms, concrete water control structures, floodplain water spreader berms, and stock tanks were identified as threats to floodplains and associated habitat. Almost half of 27 identified lateral channel berms (48%) have been breached and 15% have experienced lateral scour; 18% of 218 shorter water spreader berms have been breached and 17% have experienced lateral scour. A relatively small number of 117 stock tanks (6%) are identified as structurally compromised based on analysis of aerial imagery, although many currently do not provide consistent water supplies. In some cases, the onset of localized disturbance is recent enough that opportunities for mitigation can be identified to alter the potentially damaging erosion trajectories that are ultimately driven by regional geomorphic instability. Understanding the effects of prior land use and remnant structures on channel and floodplain morphologic condition is critical because both current land management and future land use options are constrained by inherited land use legacy effects. Published 2017. This article is a U.S. Government work and is in the public domain in the USA

High temporal resolution modeling of the impact of rain, tides, and sea level rise on water table flooding in the Arch Creek basin, Miami-Dade County Florida USA

Modeling of groundwater levels in a portion of the low-lying coastal Arch Creek basin in northern Miami-Dade County in Southeast Florida USA, which is subject to repetitive flooding, reveals that rain-induced short-term water table rises can be viewed as a primary driver of flooding events under current conditions. Areas below 0.9m North American Vertical Datum (NAVD) elevation are particularly vulnerable and areas below 1.5m NAVD are vulnerable to exceptionally large rainfall events. Long-term water table rise is evident in the groundwater data, and the rate appears to be consistent with local rates of sea level rise. Linear extrapolation of long-term observed groundwater levels to 2060 suggest roughly a doubling of the number of days when groundwater levels exceed 0.9m NAVD and a threefold increase in the number of days when levels exceed 1.5m NAVD. Projected sea level rise of 0.61m by 2060 together with increased rainfall lead to a model prediction of frequent groundwater-related flooding in areas<0.9m NAVD. However, current simulations do not consider the range of rainfall events that have led to water table elevations>1.5m NAVD and widespread flooding of the area in the past. Tidal fluctuations in the water table are predicted to be more pronounced within 600m of a tidally influenced water control structure that is hydrodynamically connected to Biscayne Bay. The inland influence of tidal fluctuations appears to increase with increased sea level, but the principal driver of high groundwater levels under the 2060 scenario conditions remains groundwater recharge due to rainfall events.

Swimming abilities of juvenile estuarine fishes: implications for passage at water control structures

The capability of early life history stage fishes to access nursery habitat within managed salt marshes is dependent on their ability to negotiate water control structures (WCSs). Knowledge of swimming ability and hydrodynamic preferences is essential to assess the impact of WCSs on fish movement in managed marshes. These data, however, are lacking for many common estuarine fishes, and the utility of the data for the few species examined thus far is limited. We examined critical swimming speeds and derived linear relationships between fish size and swimming speed for juveniles of six common estuarine fish species of the southeast U.S. and northern Gulf of Mexico coasts. White mullet Mugil curema displayed the greatest swimming ability among these six species and was able to swim against currents ≥ 30 cm s−1 higher than the other species examined at the same size. The remaining species displayed lower critical swimming speeds and were classified into groups of moderate (pinfish Lagodon rhomboides, striped mullet Mugil cephalus) or slow (silver perch Bairdiella chrysoura, spotfin mojarra Eucinostomus argenteus, spot Leiostomus xanthurus) swimmers. Our results suggest that high-flow conditions at WCSs would likely preclude the passage of all but the largest juvenile fishes, and passage for most juveniles would occur under low-flow conditions; these flows at WCSs are dictated largely by site-specific tidal and weather conditions.

Application of key ecological attributes to assess early restoration of river floodplain habitats: a case study

The Nature Conservancy acquired the Emiquon Preserve along the Illinois River, Illinois, with the primary objective of restoring ecological floodplain processes and habitats that promote and sustain native species and communities. The Conservancy convened an Emiquon Science Advisory Council prior to restoration implementation that identified key ecological attributes (KEAs) for riverine and backwater targets, KEA indicators, and acceptable ranges for those indicators. We assessed the application of this methodology to evaluate status of conservation targets and to inform future science and management at Emiquon. The KEA framework provided an important function of directing a systematic monitoring program that provided fundamental data on changing environmental conditions that were incorporated into annual target evaluations. Data show that 46–55% of all indicators were within acceptable ranges prior to reconnection of the preserve with the Illinois River. Recent completion of a water control structure represents a critical intervention that provides potential to improve conservation status of those floodplain and riverine targets that depend on water management and river connectivity. Continued review and modification of the KEA model in conjunction with a strategic monitoring program will provide critical information to guide relevant management decisions and testable hypotheses to reduce potential threats and achieve future restoration goals.