Water Control Structures Research Articles

FISHPOND STATUS MAPPING USING RADAR REMOTE SENSING

Abstract. The identification and monitoring of the status of all fishponds with Fishpond Lease Agreements (FLAs) in the Philippines is limited mainly to site visits. However, this approach is tedious, time-consuming, and costly due to the sheer number and locations of fishponds. This study explores the use of radar remote sensing in expediting the mapping of fishpond status (i.e., active, abandoned). Historical Sentinel-1A SAR images acquired from 2022–2023 covering identified fishpond areas were analysed. Several temporal statistics of their sigma nought backscatter values were calculated per polarization (i.e., VV and VH). Non-fishpond areas were masked out, and then Principal Component Analysis was applied to the stacked temporal statistics images. Afterwards, K-Means Cluster classification was applied to the first 7 components of the resulting PCA images to generate 4 classes. The resulting class with relatively low backscatter values is identified as water; “intermittent” water if their backscatter values vary greatly; and non-water or vegetated if their backscatter values are relatively high. Status was determined based mainly on the dominant class in each plot. Water class dominated plots are considered active; non-water or vegetated class dominated plots and plots that are covered mostly by “intermittent” water class are labelled as abandoned. Based on field-validated data, active fishponds, and old, abandoned fishponds (e.g., already have mangroves, or have no water control structures) were easier to correctly map, while abandoned fishpond with certain characteristics were harder to correctly identify. The approach is promising and can help BFAR map and monitor the fishponds in the country.

Evaluation of Small‐Scale Irrigation Scheme Performance and Proposed Alternative Mitigation for Improved Water Management on Wezeqa and Gatto Irrigation Schemes, Southern, Ethiopia

The performance of irrigation schemes in Ethiopia is too low due to a lack of proper system management, water control structure, and strong water user association. This study aimed to assess small‐scale irrigation scheme’s performance and proposed alternative mitigation for improved water management. Direct measurement, laboratory analysis, field observation, and stakeholder interviews were used to collect the primary data. The average conveyance efficiency, water surface elevation ratio, canal delivery capacity, adequacy, and equity of the Wezeqa and Gatto irrigation schemes were 86.37% and 75.4%, 55% and 60.3%, 71% and 55.8%, 0.68 and 0.67, and 0.4 and 0.43, respectively. The mean value of application and storage efficiencies of the Wezeqa and Gatto irrigation schemes were 59.8% and 49.4% and 94.3% and 92.2%, respectively. The effectiveness of infrastructure and weir sediment ratio in the Wezeqa irrigation scheme was 24.4% and 78.5%, respectively, and almost all infrastructures in the Gatto irrigation scheme were not functional. To solve the water shortage for both systems, water‐harvesting technology was proposed having a net volume of harvesting water during the night storage of 13,093.7 and 15,897.6 m3 for Wezeka and Gatto, respectively. Therefore, adopting water‐harvesting technology and establishing strong water user associations are recommended to minimize the water scarcity problem to improve water management and sustainability.

Impact of Controlled Drainage on Crop Yield Including Within-Field Variability

Highlights A 10-m grid system was developed for spatial and temporal analysis of crop yield impacts of controlled drainage. Yields were analyzed by annual wetness classification, soil drainage class, and elevation within the field. Overall, controlled drainage significantly increased corn yield by an average of 2.3%, but not soybean yield. The grid-based analysis with a linear mixed model identified characteristics influencing CD yield effect. Abstract. Controlled drainage is the practice of using a water control structure to raise the outlet in agricultural fields during periods when drainage is unnecessary, with the primary purpose of reducing nitrate loss. The use of this practice may increase crop yields compared to free drainage because controlled drainage can capture water from precipitation as soil water and store it for crop use later in the growing season. However, results from published studies of controlled drainage have shown mixed impacts on crop yields, and the effects of field characteristics and annual weather variation on these impacts are not well understood. To analyze crop yield impacts, two controlled and two free draining plots in eastern Indiana were compared. A grid system consisting of 10 by 10 meter cells was created to obtain a balanced data set and used to analyze crop yield by year, annual wetness classification, soil drainage class, and elevation. Controlled drainage significantly increased the corn yield in six out of nine years, and the nine-year corn yield average increased by 2.3%. Soybean yield was significantly higher under controlled drainage in three out of four years, but there was no significant difference in the four-year soybean average. Years were further classified as wet, normal, or dry based on growing season precipitation, and results indicated controlled drainage had the greatest significant impact on corn yield in the dry years. Analyzing yield by soil drainage class determined that yield had the greatest response to controlled drainage on the very poorly drained soils. Controlled drainage had a significant yield benefit in corn during dry years in areas in which the elevation is more than 30 cm above the surface elevation at the outlet, and did not lead to significant differences in normal or wet years at any elevation. The grid-based analysis with a linear mixed model accounting for autocorrelation was useful for understanding within-field variability of yield response. Keywords: Controlled drainage, Crop yield, Drainage water management, Soil drainage class, Subsurface drainage.

Development of Synthetic Unit Hydrographs Using Spatial Proximity Regionalization for the Makiling Forest Reserve, Philippines

There is a dearth of streamflow data in the Philippines to generate hydrographs needed for flood forecasting and water resources assessment. A method of generating and calibrating synthetic hydrographs using model simulations and spatial proximity regionalization is presented. Synthetic unit hydrographs of four storm events in the gauged watershed of Makiling Forest Reserve were generated using Soil Conservation Service Unit Hydrograph, Clark Unit Hydrograph, and Snyder’s Unit Hydrograph methods. The generated synthetic hydrographs for each runoff modeling technique were calibrated with the actual hydrographs of the watershed. Snyder’s Unit Hydrograph model results were the most acceptable based on the Nash-Sutcliffe Efficiency, Index of Volumetric Fit, and Relative Error of Peak Flow. The weighted values of the calibrated watershed parameters computed using spatial proximity regionalization technique and the hyetographs derived from the Rainfall Intensity Duration Frequency Curve of the University of the Philippines Los Baños-National Agrometeorological Station were used to generate the synthetic unit hydrographs for three neighboring ungauged watersheds at 2-, 5-, 10-, 15-, 20-, 25-, 50, 100-year return periods. Total runoff volume, the magnitude of peak flows, and time to peak derived from the generated hydrographs can be used in watershed planning, water resources management, flood forecasting and the design of various water control structures.

Assessment and Mitigation of Fecal Bacteria Exports from a Coastal North Carolina Watershed

Urban runoff from the Boat House Creek watershed was suspected as a main delivery mechanism for fecal indicator bacteria (FIB) to the lower White Oak River Estuary in coastal North Carolina, but the dominant source of waste (animal or human) was unknown. Water samples from eight locations within the watershed were collected approximately monthly for two years for enumeration of Escherichia coli (E. coli), enterococci, physicochemical characterization, and microbial source tracking analyses. Concentrations and loadings of E. coli and enterococci were typically elevated during stormflow relative to baseflow conditions, and most samples (66% of enterococci and 75% of E. coli) exceeded the US EPA statistical threshold values. Concentrations of FIB were significantly higher during warm relative to colder months. Human sources of FIB were not observed in the samples, and FIB concentrations increased in locations with wider buffers, thus wildlife was the suspected main FIB source. Stormwater control measures including a rain garden, water control structures, swale modifications, and check dams were implemented to reduce runoff and FIB loadings to the estuary. Stormflow reductions of >5700 m3 year−1 are estimated from the installation of the practices. More work will be needed to improve/maintain water quality as watershed development continues.

Streamflow Reconstructions Using Tree-Ring-Based Paleo Proxies for the Sava River Basin (Slovenia)

The Sava River Basin (SRB) extends across six countries (Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Albania, and Montenegro) and is a major tributary of the Danube River (DR). The Sava River (SR) originates in the alpine region of Slovenia, and, in support of a Slovenian government initiative to increase clean, sustainable energy, multiple hydropower facilities have been constructed within the past ~20 years. Given the importance of this river system for varying demands, including energy production, information about past (paleo) drought and pluvial periods would provide important information to water managers and planners. Seasonal (April–May–June–July–August–September—AMJJAS) streamflow data were obtained for two SRB gauges (Jesenice and Catez) in Slovenia. The Jesenice gauge is in the extreme headwaters of the SR, upstream of any major water control structures, and is considered an unimpaired (minimal anthropogenic influence) gauge. The Catez gauge is located on the SR near the Slovenia–Croatia border, thus providing an estimate of streamflow leaving Slovenia (entering Croatia). The Old World Drought Atlas (OWDA) provides an annual June–July–August (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) derived from 106 tree-ring chronologies for 5414 grid points across Europe from 0 to 2012 AD. In lieu of tree-ring chronologies, this dataset was used as a proxy to reconstruct (for ~2000 years) seasonal streamflow. Prescreening methods included the correlation and temporal stability of seasonal streamflow and scPDSI cells. The retained scPDSI cells were then used as predictors (independent variables) to reconstruct streamflow (predictive and/or dependent variables) in regression-based models. This resulted in highly skillful reconstructions of SRB seasonal streamflow from 0 to 2012 AD. The reconstructions were evaluated, and both low flow (i.e., drought) and high flow (i.e., pluvial) periods were identified for various filters (5-year to 30-year). When evaluating the most recent ~20 years (2000 to present), multiple low-flow (drought) periods were identified. For various filters (5-year to 15-year), the 2003 end-year consistently ranked as one of the lowest periods, while the 21-year period ending in 2012 was the lowest flow period in the ~2000-year reconstructed-observed-historic period of record. The ~30-year period ending in 2020 was the lowest flow period since the early 6th century. A decrease in pluvial (wet) periods was identified in the observed-historic record when compared to the paleo record, again confirming an apparent decline in streamflow. Given the increased activities (construction of water control structures) impacting the Sava River, the results provide important information to water managers and planners.

Algal blooms in a river-dominated estuary and nearshore region of Florida, USA: the influence of regulated discharges from water control structures on hydrologic and nutrient conditions

Flow-regulated discharges of water from control structures into estuaries result in hydrologic and water chemistry conditions that impact spatial and temporal variability in the structure and biomass of phytoplankton communities, including the potential for harmful algal blooms (HABs). The relationships between regulated Caloosahatchee River (i.e., C-43 Canal) discharges and phytoplankton communities in the Caloosahatchee Estuary and adjacent nearshore regions on the southwest coast of Florida were investigated during two study periods, 2009–2010 and 2018–2019. During periods of low to moderate discharge rates, when mesohaline conditions predominated in the estuary, and water residence times were comparatively long, major blooms of the HAB dinoflagellate species Akashiwo sanguinea were observed in the estuary. Periods of high discharge were characterized by comparatively low phytoplankton biomass in the estuary and greater influence of a wide range of freshwater taxa in the upper reaches. By contrast, intense blooms of the toxic dinoflagellate Karenia brevis in the nearshore region outside of the estuary were observed during high discharge periods in 2018–2019. The latter events were significantly associated with elevated levels of nitrogen in the estuary compared to lower average concentrations in the 2009–2010 study period. The relationships observed in this study provide insights into the importance of managing regulated discharge regimes to minimize adverse impacts of HABs on the health of the estuary and related coastal environments.

LAGOS‐US RESERVOIR: A database classifying conterminous U.S. lakes 4 ha and larger as natural lakes or reservoir lakes

AbstractThe LAGOS‐US RESERVOIR data module classifies all 137,465 lakes ≥ 4 ha in the conterminous U.S. into three categories using a machine learning predictive model based on visual interpretation of lake outlines and a lake shape classification rule. Natural Lakes (NLs) are defined as naturally formed, lacking large, flow‐altering structures; Reservoir Class A's (RSVR_A) are defined as lakes likely human‐made or human‐altered by a large water control structure; and Reservoir Class B's (RSVR_Bs) are lakes likely human‐made but are not connected to streams and have a shape rare in NLs. We trained machine learning models on 12,162 manually classified lakes to predict assignment as an NL or RSVR, then further classified RSVRs based on NHD Fcodes, isolation, and angularity. Our classification indicates that > 46% of lakes ≥ 4 ha in the conterminous U.S. are reservoir lakes. These data can be easily combined with other LAGOS‐US modules and U.S. national databases for the broad‐scale study of reservoir lakes and NLs.

COST ANALYSIS OF WATER RESOURCES MANAGEMENT SERVICES BELANTI II IRRIGATION AREA CENTRAL KALIMANTAN PROVINCE

The Belanti II Swamp Irrigation Area in Pulang Pisau Regency, Central Kalimantan, spans 3,275 Ha. Water management activities, necessitated for sustained irrigation, incur the Water Resources Management Service Fee (BJPSDA), calculated on cost recovery principles. This study aims to (1) Determine the BJPSDA value by considering the economic benefit factor, (2) Assess farmers' Ability To Pay (ATP) and Willingness To Pay (WTP) for BJPSDA, and (3) Evaluate the Belanti II swamp irrigation network and optimization efforts. The BJPSDA in Belanti II is Rp5,625,504,000, with agricultural benefits contributing Rp51,468,721,052.40 (51.86% of NME). The cost is Rp570,151.69/Ha or Rp101/m3. Farmer ATP and WTP for BJPSDA are Rp54/m3. The irrigation system lacks proper water flow regulation structures, but optimization efforts include channel normalization and water control structures. To enhance leaching ability, 500 m3/ha/day of fresh water is needed. Structures like weirs and flap gates regulate water supply during high and low tides, respectively. These initiatives aim to ensure consistent irrigation and sustainable water resource management in Belanti II.

One-way flow system for improvement of the acid sulfate soil reclamation process in the Belanti II tidal swamp irrigation network, Central Kalimantan, Indonesia.

Belanti II tidal irrigation network was developed in 1980 on acid sulphate soil with an area of approximately 3976 ha. Belanti II has one primary channel and several secondary channels, without any water structures that regulate the direction of flow. Two-way flow occurs in the channel, supplying fresh water from the river at high tide and flowing back into the river at low tide. This two-way flow system inhibits the leaching process of acid sulphate soil. Up to now, acid sulfate soils are still found at a depth of 50-75 cm with a pH of 2.5 ~ 3.5. A one-way flow system is expected to improve water circulation, assisted by channel rehabilitation, collector channels and water control structures. The spillway structure at the secondary channel regulates the freshwater supply at high tide and the flap gate at the end regulates the flow of water to the collector channel at low tide. Hydraulic analysis was carried out using HEC-RAS modelling. The results showed the ability of the system to supply fresh water, flushing/leaching acid sulfate water and drainage the toxic water. The effectiveness of the system is evaluated regarding the direction and the volume of freshwater flowing into the secondary channel.

Too Much Freshwater, Not Enough, or Just Right? Long-Term Trawl Monitoring Demonstrates the Impact of Canals that Altered Freshwater Flow to Three Bays in SW Florida

Understanding the impact of anthropogenically altering freshwater flow to estuaries is a growing information need for coastal managers. Due to differences in watershed development, drainage canals, and water control structures, the Ten Thousand Islands area of southwest Florida provides an ecosystem-scale opportunity to investigate the influence of both more, and less, freshwater flow to coastal bays compared to locations with more natural hydrology. Bottom trawl and water quality data spanning 20 years were used to investigate how environmental and hydrological differences among three bays affect community structure of small estuarine fishes. Relationships between fish community structure and salinity and temperature variables were evaluated over timescales from 1 day to 3 months prior to each trawl. Longer-term aspects of temperature (i.e., 2–3 months) exhibited the highest correlations in all bays, suggesting that spawning cycles are the main cause of seasonal changes in fish communities, rather than differences in freshwater flow. Despite major contrasts in watershed manipulation and the seasonal salinity of one bay being much less than the others, the bays differed primarily based on relative abundances of more common species rather than due to unique suites of species being present. Truly freshwater conditions were never detected, and high salinity conditions were experienced in all bays during dry seasons. This likely prevents a community shift to freshwater species. The range in flow characteristics among bays and general similarity in fish communities suggest that conditions will remain within the tolerance of most fishes in all three bays following restoration to more saline conditions.

Thirty years of water management research for rice in sub-Saharan Africa: Achievement and perspectives

Rice is one of the major staple foods in sub-Saharan Africa (SSA) and is mainly grown in three environments: rainfed upland and rainfed and irrigated lowlands. In all rice-growing environments, the yield gap (the difference between the potential yield in irrigated lowland or water-limited yield in rainfed lowland and upland and the actual yield obtained by farmers) is largely due to a wide range of constraints including water-related issues. This paper aims to review water management research for rice cultivation in SSA. Major water-related constraints to rice production include drought, flooding, iron toxicity, and soil salinity. A wide range of technologies has been tested by Africa Rice Center (AfricaRice) and its partners for their potential to address some of the water-related challenges across SSA. In the irrigated lowlands, the system of rice intensification and alternate wetting and drying significantly reduced water use, while the pre-conditions to maintain grain yield and quality compared to continuous flooding were identified. Salinity problems caused by the standing water layer could be addressed by flushing and leaching. In the rainfed lowlands, water control structures, Sawah rice production system, and the Smart-Valleys approach for land and water development improved water availability and grain yield compared to traditional water management practices. In the rainfed uplands, supplemental irrigation, mulching, and conservation agriculture mitigated the effects of drought on rice yield. The Participatory Learning and Action Research (PLAR) approach was developed to work with and educate communities to help them implement improved water management technologies. Most of the research assessed a few indicators such as rice yield, water use, water productivity at the field level. There has been limited research on the cost-benefit of water management technologies, enabling conditions and business models for their large-scale adoption, as well as their impact on farmers’ livelihoods, particularly on women and youth. Besides, limited research has been conducted on water management design for crop diversification, landscape-level water management, and iron toxicity mitigation, particularly in lowlands. Filling these research gaps could contribute to sustainable water resources management and sustainable intensification of rice-based systems in SSA. • Research on water management for rice cultivation in sub-Saharan Africa was reviewed. • The majority of studies aimed at improving water control in rainfed lowlands. • The studies focused mostly on improving rice yield and water productivity. • Less attention was given to cost-benefits and impact of water control technologies. • Water management was mostly studied at the field- rather than at landscape-level.

Computing Cost and Time Contingency for Box Culverts Construction Projects using Integrated Risk Management Technique

Construction and rehabilitation of water control structures in Egypt considered as an important project, as it influences the usage of water resources in Egypt which become limited resources due to water scarcity existed in the last decades. Also these projects helps in the optimization of water resources, Moreover it helps in the growth of agricultural and industrial sector. Project Risk Management (RMP) is considered as a vital and important tool in decision making, thus RMP used as a planning management system to detect risks affecting project deliverables; such as cost and time target. This research shows how to optimize the deliverables for construction of box culverts in Egypt, through a well-defined risk management framework and real case study for a certain project executed in the last decade. Finally, this study shows how to calculate cost and time contingency for these projects through an integrated risk management technique. Finally this study shows hazard risk identification and assessment for these type of projects. The conclusion of this study show that the cost contingency needed to resolve different risk factors arise in the shown case study is to increase the estimated budget with average value 11.50 percent on the total estimated budget, as well as the time contingency is found with average value 16.00 percent to be added over the total original baseline schedule of the construction project.

Testing some grouping methods to achieve a low error quantile estimate for high resolution (0.25° x 0.25°) precipitation data

The study focuses on the estimation of a technique, a method for developing a phenomenon, to obtain a quantile with minimal or low error (AR and R-RMSE bias). To arrive at such a solution, a case study of the Mahanadi River system (Mahanadi Basin) was conducted along with the integration of various techniques available in past and present literature, to come up with a novel solution. Which could answer practical questions in water resource planning and management for addressing a wide range of problems such as meteorological draught analysis, agricultural planning, precipitation forecasting and downscaling, design of water control and conveyance structures, and land-use planning and management. A gridded rainfall data set of resolution 0.25° x 0.25° (1901 – 2017) obtained from IMD Pune is used to calculate the statistics that will be used for the regionalization of precipitation. Other attributes or variables used for regionalization are seasonality measurements and location parameters (latitude, longitude, and elevation). The L-moment statistics are computed from the time series rainfall data and the ratios of the L-coefficient of variance and the L-coefficient of skewness, i.e., the L-moment ratio, are the main components in computing quantile estimates of selected regions for effective regional frequency analysis. To determine potential scenarios for homogeneous regions, the use of seasonal extreme precipitation will serve as a basis for regionalization.

Influences of channel and floodplain modification on expansion of woody vegetation into Catahoula Lake, Louisiana, USA

AbstractEcosystem structure of wetlands in managed floodplains depends on hydrological processes controlled by geomorphology and water management. Overlapping effects of direct modifications and geomorphic adjustments to management can combine to trigger changes to floodplain ecosystem structure. We examined the case of woody vegetation encroaching into the depressional Catahoula Lake, Louisiana, in the context of regional hydrologic and geomorphic modification in the floodplain of the Mississippi River. Historical aerial photographs indicated woody encroachment into Catahoula Lake for at least 80 years, and the rate of expansion has increased in recent decades. Historical stage analysis revealed that the downstream Red–Atchafalaya–Mississippi River system controls the lower limit of the lake water level when the large rivers are high, but channel enlargement and other hydrological changes there have reduced the frequency of backwater flooding by 42% since 1880. In addition, operation of the water control structure on the lake has altered its hydrological regime to be more regular among years. Historic stage analysis revealed current lake levels are lower in the high‐water spring, less variable in the dry period, and lack the extreme high‐water events of 100+ years ago, all of which facilitate the expansion of woody vegetation.

Interactions of a temperate North American fish community with a very low head hydropower facility in Ontario, Canada

AbstractEfforts are underway to re‐evaluate the use of existing instream infrastructure (e.g., weirs, water control dams) for the purposes of hydroelectric generation, with new very low head turbine technology that is purportedly “fish friendly” making retrofitting a viable option. This is the case at Wasdell Falls on the Severn River, ON, Canada, where the first very low head (VLH) turbines in Canada were put into operation at a long‐standing low‐head dam site. There is little information regarding fish usage of areas upstream from these structures and how this may relate to entrainment risk. Therefore, we assessed the risk of entrainment based on fish use of the forebay areas upstream from the infrastructure, including the forebay of three operating VLH turbines. Acoustic telemetry was used to determine movements and entrainment events of eight north temperate fish species. Entrainment through the VLH turbines did not occur over the course of one year, however, several fish did move downstream via other paths (e.g., over the water control structure). Forebay use was exclusive to rock bass, smallmouth bass, northern pike and largemouth bass, whereas channel catfish, walleye, white sucker and pumpkinseed avoided the forebay. When near the dam, fish tended to select deeper areas located away from the VLH forebay. Fish use of the VLH forebay was limited to brief forays indicating exploratory movements rather than prolonged residence. The findings suggest that entrainment risk at this VLH turbine site is low for the species and life stages studied.

Hydrology management influences nest survival but not clutch size in Lesser Scaup

Components of reproductive success such as clutch size and nest survival may greatly affect avian population growth rates. Understanding how environmental conditions influence temporal variation in these demographic parameters could thus provide valuable insight into best management practices for species of concern. One such species that could benefit from a better understanding of such processes is Lesser Scaup (<em>Aythya affinis</em>), whose overall abundance in North America has declined since the early 1980s. We used a long-term study (2005–2019) of Lesser Scaup demography at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, to examine how the management of wetland conditions influenced within- and across-year temporal variation in clutch size and nest survival. Predicted clutch size varied more across nest initiation dates (6.18–10.05 eggs) within years than it did across years (7.51–8.38 eggs), and none of the covariates we examined were significantly related to clutch size across years. Nest daily survival rates varied substantially across days within breeding seasons (e.g., 2018: 0.38–0.985), and annual mean nest survival varied greatly across years (0.27–0.58). Furthermore, seasonal chronology of managed wetland water levels influenced nest survival such that years when water levels gradually rose to a maximum late in the breeding season, relative to mean nest initiation date, resulted in the highest nest survival. These findings collectively suggest that when flows can be manipulated with water control structures, efforts to manage the chronology of water levels at watershed and local wetland scales could improve nest survival, whereas such management efforts will not likely affect clutch sizes.

An Application of Computational Fluid Dynamics to the Hydraulic Analysis of a Water Intake Tower

Hydraulic engineers must sometimes perform hydraulic analyses of water control structures to evaluate system behavior under current operational demands and determine if design improvements may be needed. This paper summarizes an example of how computational fluid dynamics can be used for this purpose. A computational fluid dynamics model of a water intake tower that is connected to a pump station though a tunnel was constructed using the commercial software FLOW-3D. The model was used to evaluate head losses through the structure for a desired sustained pumping rate. The computational fluid dynamics modeling results for the intake tower indicate that if the target discharge rate is to be sustained while the upstream delivery canal stage is at its design stage, the head loss across the structure will comprise most of the head loss incurred through the water delivery system. Moreover, an examination of model output revealed certain features of the structure’s hydraulic design that result in excessive losses within the tower and near the entrance of the downstream tunnel.

Variation in larval Gulf Menhaden diet, growth and condition during an atypical winter freshwater-discharge event in the northern Gulf of Mexico

In January 2016, historic levels of rainfall in the upper Mississippi River Basin prompted the earliest opening of the Bonnet Carré Spillway, a water control structure on the Mississippi River that diverts flood-stage river water through an alternate pathway (Lake Pontchartrain) into the northern Gulf of Mexico. This unprecedented winter opening of the spillway coincided with the spawning season and larval ingress period for Gulf Menhaden, a forage fish species that supports the largest commercial fishery in the region. Oceanographic observations and plankton samples were collected in the Mississippi Bight region shortly after the Bonnet Carré Spillway winter opening to examine the impacts on larval Gulf Menhaden feeding, growth and condition. Three distinct water masses were identified based on temperature, salinity, and particle scattering (proxy for turbidity) characteristics. Larval Gulf Menhaden with the highest growth rates and body condition were collected in a water mass defined by relatively high temperature and salinity and relatively low turbidity and zooplankton (prey) abundance. In contrast, larvae with the slowest growth rates and poor body condition were collected in a water mass with the highest zooplankton abundance, but also highest turbidity and lowest temperature and salinity. This water mass was nearest the diversion outflow and most impacted by the spillway opening. Our results indicate that the anomalous freshwater discharge event resulted in hydrographic conditions that diminished otherwise favorable larval fish foraging habitat with abundant zooplankton prey. These findings suggest that the recent trend of Bonnet Carré Spillway openings may result in negative consequences for larval fish survival and subsequent fishery recruitment.

Evaluation of Electrical and Electromagnetic Geophysical Techniques to Inspect Earthen Dam and Levee Structures in Arkansas

Within the State of Arkansas, there is an increasing number of aging dams and levees that have little to no documentation concerning their construction or composition. Surface geophysical surveys offer a non-intrusive method for investigating these structures to describe their lithologic makeup, evaluate the materials constructed upon, and identify potential flow paths through them. Techniques such as electrical resistivity tomography, seismic refraction, and electromagnetic induction have been used to image dams and levees. They require additional information from geologic outcrops, geotechnical borings, or drill cores to make informed geologic interpretations of the geophysical models. These geologic models then allow the owners of these structures to make more informed decisions about their operation and maintenance. Between 2011 and 2018, the U.S. Geological Survey conducted geophysical and geotechnical investigations of three earthen structures in Arkansas. Electrical and electromagnetic geophysical data were used to develop lithologic models of these structures and characterize the underlying geology. Self-potential surveys were utilized to detect the movement of water through these structures and identify any possible seepage pathways. Geotechnical methods such as electric and hydraulic direct-push well logs and cores acted as a control on the geophysical interpretations and a confirmation of anomalies. This integrated approach detected the lack of an impermeable core within a levee, imaged a change in lithology of the bedrock forming the seal beneath a gravity dam, and identified a potential seepage feature within the core of an earthen dam. These results further support that this method of extending known lithologic features via surface and borehole geophysics is a useful approach for characterizing earthen water-control structures.