Water Impoundment Research Articles

Water quality variation in tributaries of the Three Gorges Reservoir from 2000 to 2015

The Three Gorges Reservoir (TGR) underwent staged impoundment during 2003−2010. Periodic water impoundment included drainage (March to early June), low water level (June to August), impoundment (September to October), and high water level (November to February) periods. However, the impacts of the Three Gorges Dam (TGD) and impoundment on water quality of TGR tributaries remain poorly understood, especially in the long term and across the entire TGR drainage basin. Herein, water quality and hydrological indices of 27 tributaries, eutrophication of 38 tributaries, and pollution load of the TGR were determined during 2000–2015 to explore spatiotemporal variations in water quality. The results revealed slower flow velocity in tributaries and an extended residence time with the water level rising, and the water quality of tributaries was mainly affected by the mainstream backwater movement. Water quality was good in more than 60% of tested sites, had the best condition in the impoundment period, and it increased over time. Spatially, water quality in tributary upstream was better than in the backwater area, and worst in the tributary estuary. Among water quality indices, total nitrogen (TN) and total phosphorus (TP) were the key pollution indices, with median range of 1.619−2.739 and 0.088−0.277 mg/L, respectively. Additionally, water quality indices of TGR tributaries displayed temporal and spatial heterogeneity due to different hydrodynamic and pollution load conditions. A total of 38 tributaries displayed eutrophication, the frequency of blooms concentrated in spring and increased from the upper tributaries to the downstream area. These results expanded the theory of hydrodynamic variation and the associated evolution of the water environment after impoundment, could provide theoretical references for water quality management in river-type reservoir.

Comparison of hydrodynamic and sediment transport model for dam break analysis over mobile bed

A dam failure causing uncontrolled release of impounded water can cause considerable damage to life and properties. The intensity of the failure of dams varies depending on the extent of the flood characteristics, the size of the flooded area, the size of the population at risk and the time available for warning. In addition to this, huge morphological changes also occur at the downstream of the dam due to the dam break flood. This leads to the need for an analysis of sediment transport, together with the hydrodynamic analysis of the dam break flow, to provide a realistic picture of its devastating impact. This study uses an open source CFD software named TELEMAC-MASCARET to prepare a numerical model to simulate a 2-D dam break flow over mobile bed. A hydrodynamic model and an integrated model that comprises of sediment transport analysis are prepared and the results are compared to determine the most effective model for a 2-D dam break analysis. The study indicates that the integrated model performs better than the hydrodynamic model and replicates the real scenario more adequately.

Application of numerical modeling to reservoir immersion assessment and control in dual-formation hydrogeological unit

Abstract Reservoir immersion is a serious environmental geological issue in a dual-formation structural reservoir bank (DFB) induced by dynamic surface water impoundment (SWI) that has implications for low-lying farmland and buried infrastructure. It is a major challenge to identify the dynamic immersion process and make economic and scientific joint mitigation measures for controlling groundwater immersion. Here, we develop a three-dimensional groundwater flow model and apply it to evaluate and control reservoir immersion in the typical low-lying DFB of Xingan Navigation and Power Junction Project (XGNPJ) across Ganjiang River in Jiangxi Province, China. The field-scale model is well calibrated to predict where the groundwater immersion could potentially occur. Furthermore, the effectiveness of the countermeasures adopted for the reduction of reservoir immersion areas were analysed based on the simulation model by considering the projected future combination scenarios of engineering measures. Results indicate that without engineering mitigation measures, SWI generates groundwater inundation across 23% of the total study area. Comprehensive comparative analysis on different seepage control schemes reveals that the joint engineering measures can effectively control the immersion range to 5% of the total area. The findings can provide scientific basis for groundwater immersion assessment and guide immersion control of XGNPJ project.

Multimetric approach in the effects of small impoundments on stream water quality: Case study of Faylor and Walker Lakes on Middle Creek, Snyder County, PA

AbstractIn recent years, dams have received extensive scrutiny for their effects on stream and river systems throughout the United States. Dams vary greatly in size and scale, but investigations often focus on large‐scale dams due to their visibility in the public eye and pronounced impact. This can result in smaller and less impactful impoundments being overlooked, despite the cumulative effects these dams can have on higher order aquatic systems. Two small water impoundments: Walker and Faylor Lakes located, respectively, on the north and west branches of Middle Creek in Snyder County; Pennsylvania have demonstrated an impact on Middle Creek. This study focused on using onsite physical properties, grab samples for chemical analysis and macroinvertebrate samples to determine and compare the effects of the two impoundments on Middle Creek. Both upstream and downstream sites from the dams were sampled. All sites were sampled for physical variables using the YSI Multimeter and chemical concentrations of several cations and anions using Ion Chromatography (IC). A Water Quality Index (WQI) was constructed based on 11 different parameters. All parameters were positively correlated. Data show that the physical and chemical changes to the streams, are caused by the dams and are affecting the biological communities in the downstream water course. Walker Lake was found to have a much greater negative impact on the north branch of Middle Creek causing degradation to the water in relation to certain parameters. Greater concentrations of NH4+, BOD5 and a decreasing WQI downstream of the Walker Dam, as well as several different macroinvertebrate indices indicate this negative impact. Faylor Lake Dam did not have a large impact on the west branch of Middle Creek with regard to any particular variable measured. Overall, small reservoirs can have substantial impacts on the streams they impound especially when considering the morphology and design.

FE analysis of the shaft lock chamber in Mengdigou Hydropower Project considering construction and service cases

The geological conditions of the diversion tunnel of Mengdigou hydropower station are very complex. Faults, joint fissures and groundwater are developed, and the underground chambers in the entrance end of the diversion tunnel are large scale, and the mechanical deformation induced by excavation and unloading is complicated. In order to investigate the stress and deformation in the shaft chamber surrounding rock during the period of construction and running, numerical simulation method was adopted to simulate construction process, discharging, water impoundment and power generation cases. The following conclusions are obtained: 1) during construction, the surrounding rock around the transition section of shaft lock chamber is stable; 2) during the period of discharging, water storage and power generation, the tensile stress in the inner part of the joint of gate slot, side wall and bottom plate exceeds the tensile strength of lining concrete. It is suggested to strengthen the reinforcement in these zones, and the concrete compressive stress in the compression area does not exceed the compressive strength. The results from this research could be taken as the reference for the design and construction of the project.

The Ilisu Dam and Its Impact on the Mesopotamian Marshes of Iraq: Implications for the Future Directions of International Water Law

Abstract The law of international watercourses has been successful in providing some measure of assistance in conflict avoidance and resolution. However, evolution of this body of law, which has been gradual in nature, is facing challenges adapting to climate change and its grave consequences. Climate change is causing the glaciers of the world to melt, and resulting in unpredictable shifts in patterns of rainfall, thus seriously impacting shared watercourses. The history and ecology of the Tigris Euphrates Basin, and the issues surrounding Turkey’s recent impoundment of water behind the Ilisu Dam on the Tigris, provide an example highlighting such challenges. This monograph argues that international collaboration over transboundary watercourses is imperative for maintaining peace and stability and should force us to think of new ways to address these newly emerging and growing challenges in this field.

Assimilation of Ground‐Based GPS Observations of Vertical Displacement into a Land Surface Model to Improve Terrestrial Water Storage Estimates

AbstractGround‐based Global Positioning System (GPS) observations of vertical surface displacement can be used to study terrestrial water storage (TWS) change after properly accounting for nonhydrological loading effects. This study systematically merged ground‐based GPS observations of vertical displacement into a land surface model in order to better estimate TWS. Assimilation was conducted across two snow‐dominated watersheds in the western United States using a one‐dimensional ensemble Kalman filter (EnkF). Modeled estimates were compared against TWS retrievals derived from the Gravity Recovery and Climate Experiment (GRACE) mission and in situ measurements of snow water equivalent (SWE), soil moisture, and runoff. The GPS data assimilation (GPS DA) technique improves prediction skill of TWS anomalies relative to the Open Loop (OL; model run without assimilation) when compared against GRACE TWS retrievals, especially during an extended drought period post‐2011 (e.g., correlation coefficient ROL = 0.46 and RGPSDA = 0.82 in the Great Basin). Furthermore, GPS DA improves SWE estimation with improved R values found over 76% and 69% of all pixels collocated with in situ stations in the Great Basin and Upper Colorado watersheds, respectively. GPS DA estimates of surface soil moisture and runoff, however, exhibit degraded performance relative to the OL due to the limited sensitivity of GPS observations to surface soil moisture variations and the lack of a dynamic surface routing scheme as well as other missing model physics (e.g., river and dam regulation, irrigation‐related water withdrawals, surface water impoundments) that are not included in the Catchment Land Surface Model.

The downstream migration success of Atlantic salmon (Salmo salar) smolts through natural and impounded standing waters

Atlantic salmon (Salmo salar) smolt migration through standing waters is generally known to be associated with slow migration speed and low success. Most previous studies have however been conducted on impounded waters. The bathymetry and specifically the flow dynamics around the outlets differ markedly between impounded lakes and naturally draining lakes. To date no study has attempted to disentangle the effects of the impoundment from that of standing water itself. This question was tested in a single naturally draining standing water and two impounded standing waters within a single catchment using fish tagged with acoustic and PIT tags (in three and two lakes, respectively). Overall migration success (river to estuary) was very low (10%); migration success through the lakes was also very low (total loss rates range: 31 to 55%; 16 to 53%.km−1) compared with migration in the river downstream of the lakes (range: 3.9 to 10.8%.km−1). Migration success was no lower in impounded lakes compared with the naturally draining lake. 49% of directional movements were in a direction opposite to the migration pathway, indicating that a lack of navigational cues may be in-part responsible for low migration success. We tentatively conclude that successful migration through standing waters without strong directional cues may be more stochastic than previously thought. We suggest that at least for some impoundments (as shown here), the impoundment per se may not reduce migration success, its greater effect being the creation of the standing water through which smolts are required to migrate. However, any impoundment effect is likely to be dependent upon a combination of lake basin shape, the exit route from the lake and the navigational cues available to smolts.

Evaluating the eutrophication risk of an artificial tidal lagoon

With increased nutrient inputs to estuaries in recent decades exacerbating their susceptibility to eutrophication, assessment of the response of individual estuaries to nutrient enrichment is attracting considerable attention. Nonetheless, the impact of tidal energy extraction on estuarine nutrient dynamics and the risk of eutrophication has been largely overlooked despite the detrimental consequences of eutrophication on ecosystem functioning. It is understood that tidal energy schemes such as the tidal lagoon previously proposed in Swansea Bay would alter tidal flow characteristics, potentially having knock-on impacts on physical estuarine characteristics and ecological processes in the impounded area. This study examined the existing physical estuarine characteristics in Swansea Bay and evaluated the risk of eutrophication following tidal power plant operation under ebb-only and two-way strategies using a simple risk assessment model. Two surveys were conducted to measure in-situ temperature, salinity, dissolved oxygen, chlorophyll-a, dissolved inorganic nitrogen and turbidity in the water column at 12 sampling stations selected to cover the location in the tidal energy scheme proposal. The water column was found to be nutrient enriched and essentially vertically homogenous with no strong evidence of stratification. High dissolved oxygen, low turbidity and high phytoplankton biomass indicated by the chlorophyll-a concentrations were observed. The bay did not show any signs of eutrophication as the phytoplankton biomass did not reach the level typical of harmful algal blooms and oxygen depletion was not observed indicating that eutrophication is not currently present in the bay. Based on numerical model predictions, the bay was found to exhibit a moderate response to nutrient enrichment with no risk of eutrophication and no net change in its status following the operation of the lagoon under both ebb-only and two-way operational modes. These findings suggest that the management strategies for protecting water quality in heavily modified estuaries such as Swansea Bay may not need to be altered following the operation of a tidal lagoon. But given the conditions for phytoplankton growth are likely to be more favourable under ebb-only operational mode compared to two-way operational mode, measures that control nutrient inputs to the impounded water column within the lagoon should be considered under the ebb-only operational mode as a prudent precautionary step.

Boat ramps facilitate the dispersal of the highly invasive zebra mussel (Dreissena polymorpha)

Invasive bivalves can cause widespread ecological damage, but eradication has proved difficult. Identifying the pathways of dispersal is crucial to implementing more effective biocontainment measures. We examined the distribution of the highly invasive zebra mussel (Dreissena polymorpha) in Great Britain through Species Distribution Modelling to determine the drivers of distribution and generated suitability maps to predict future dispersal. Distance to boat ramps was the most important predictor of zebra mussel establishment, accounting for 27% of variation in occurrence. Probability of occurrence was highest within 3 km upstream of boat ramps, probably due to boating activity and the impounded waters typically associated with boat ramps. Our results highlight the need for implementing stringent control measures around boat ramps, and demonstrate the value of spatially modelling species distribution to create risk maps for targeting monitoring efforts at those locations most vulnerable to invasion.

On-farm reservoir monitoring using Landsat inundation datasets

On-farm reservoirs (OFRs)—artificial water impoundments that retain water from rainfall and run-off—enable farmers to store water during the wet season to be used for crop irrigation during the dry season. However, monitoring the inter- and intra-annual change of these water bodies remains a challenging task because they are typically small (< 10 ha) and occur in high numbers. Therefore, we used two existing Landsat inundation datasets—the U.S. Geological Survey Dynamic Surface Water Extent (DSWE) and the European Commission’s Joint Research Centre (JRC) Global Monthly Water History—to assess surface water area change of OFRs located in eastern Arkansas, the third most irrigated state in the U.S. that has seen a rapid increase of OFRs occurrence. We used an existent OFRs dataset as ground-truth. We aimed (i) to compare the performance of the DSWE and the JRC when characterizing OFRs of varied sizes and (ii) to assess the impact of climate variables (i.e., precipitation and temperature) on surface water area of OFRs. We found the highest mean percent errors (MPE) in size (~20%) for OFRs between 0 and 5 ha, the smallest size class in our study. The DSWE had a smaller MPE and higher agreement with our ground-truth dataset when compared to the JRC for OFRs smaller than 5 ha (p-value < 0.05). Both inundation datasets enabled us to estimate the seasonality in surface area change of OFRs, with the highest surface water extent between March–May, the months when the region receives most of the annual precipitation. Our results showed that both DSWE and JRC can be used to enhance hydrological assessments in poorly monitored basins that have a concentration of OFRs, and the methods can be applied to other study regions if the inundation datasets are available.

Prediction equation for the fundamental vibration period of concrete gravity dams with impounded water

The design of dam structures requires advanced analysis techniques due to the dam body’s complicated interaction with its surroundings. Consequently, most of the time, it is a must to perform response history analysis during the design and assessment of dam structures. The target fundamental vibration period is necessary to generate ground motion histories compatible with the site-specific response spectrum. In this study, an equation was developed to predict the fundamental vibration period of concrete gravity dams based on an extensive database. First, a wide range of parameters to describe gravity dams’ three-dimensional (3D) geometry and their valleys are determined. A total of 19,440 different 3D numerical models with fluid and solid elements were formed, and the fundamental vibration period values were determined to create the necessary database. Then, multiple nonlinear regression analysis was conducted to propose an equation to predict the fundamental vibration period. The proposed equation could be used to accurately estimate the required fundamental vibration period during the preliminary design stage or the implementation of simplified procedures or during the spectrum matching operations.

Temporal and spatial variation in water quality in the Three Gorges Reservoir from 1998 to 2018

The Three Gorges Reservoir (TGR) underwent staged impoundment of water from 135 m to 175 m between 2003 and 2010. Periodic water impoundment was divided into drainage (March to early June), low water level (June to August), impoundment (September to October), and high water level (November to February) period. However, the impact of the Three Gorges Dam (TGD) and staged impoundment on water quality, especially in the long term, remains unclear. Herein, hydrological, pollution load, nutrient, and biochemical indices were determined for the TGR during 1998–2018. The Canadian Council of Ministers of the Environment Water Quality Index, a K-means clustering algorithm, and the Mann-Kendall (MK) test were applied to this data to explore the spatial and temporal distribution of water quality. The results show that water quality was good overall, but it before the full impoundment stage (2010) was worse than after that. The low water level period had the worst water quality among the four periods, and spatially, midstream was worst. Among water quality indices, the median total nitrogen (TN) and total phosphorus (TP) were in the range of 1.505–2.303 and 0.071–0.176 mg/L, respectively, and these were the key pollution indices. In addition, due to differences in hydrological and hydrodynamic conditions, and the regional distribution of pollution sources, water quality in the TGR displayed temporal and spatial heterogeneity. TN, TP, potassium permanganate index (CODMn), five-day biochemical oxygen demand (BOD5) and Escherichia coli (E. coli) were maximal during the low water level period, and TN, TP and E. coli were highest in midstream. MK test results revealed that nutrients pollution became worse midstream, and a gradual increase in TP caused severe algal blooms downstream. Therefore, nutritional water treatment and non-point source pollution control should be the focus of future work.

NİZİP ŞEHRİNDE SAÇAKLANMA: UZAKTAN ALGILAMA VE NÜFUS VERİSİ DEĞERLENDİRMESİ

Based on Remote Sensing image processing and Geographic Information Systems analysis, population-dependent urban structures can be accurately monitored, analysed, and potential spatial or environmental problems restrained by professional land use management. In this study, the city of Nizip, located within the province of Gaziantep, was evaluated in this perspective and its development in the last thirty years was determined. The satellite images of 1990 and 2019 were evaluated within the framework of CORINE land classification system. The controlled classification method was implemented in the analysis and the city's growth rate and direction were determined while land cover changes were investigated both statistically and spatially. According to the analysis, residential areas in the study area, which were 555 ha in 1990, exceeded 1000 ha in 2019, due to industrialization and population growth. Urban sprawl was observed in NE and E directions. In addition, the bare lands of the city have been converted to dry agricultural lands in the last three decades which is supposedly due to long term climate effects. Along with the increasing industrialization movement in this period, the population increased by 30% on average in the central neighbourhoods. Migration from evacuated villages to the city centre following dam construction and water impoundment phases has increased the population. Rapid urbanization is also observed alongside newly built highways and motorways. Regarding increasing population movements in recent years, it is predicted that there could be spatial and environmental problems due to rapid and unplanned urbanization in Nizip city. It is stated that the elimination of these problems can be carried out through accurate and planned land use decision support systems.

Forest Management Under Megadrought: Urgent Needs at Finer Scale and Higher Intensity

Drought and warming increasingly are causing widespread tree die-offs and extreme wildfires. Forest managers are struggling to improve anticipatory forest management practices given more frequent, extensive, and severe wildfire and tree die-off events triggered by “hotter drought”—drought under warmer than historical conditions. Of even greater concern is the increasing probability of multi-year droughts, or “megadroughts”—persistent droughts that span years to decades, and that under a still-warming climate, will also be hotter than historical norms. Megadroughts under warmer temperatures are disconcerting because of their potential to trigger more severe forest die-off, fire cycles, pathogens, and insect outbreaks. In this Perspective, we identify potential anticipatory and/or concurrent options for non-timber forest management actions under megadrought, which by necessity are focused more at finer spatial scales such as the stand level using higher-intensity management. These management actions build on silvicultural practices focused on growth and yield (but not harvest). Current management options that can be focused at finer scales include key silvicultural practices: selective thinning; use of carefully selected forward-thinking seed mixes; site contouring; vegetation and pest management; soil erosion control; and fire management. For the extreme challenges posed by megadroughts, management will necessarily focus even more on finer-scale, higher-intensity actions for priority locations such as fostering stand refugia; assisted stand recovery via soil amendments; enhanced root development; deep soil water retention; and shallow water impoundments. Drought-induced forest die-off from megadrought likely will lead to fundamental changes in the structure, function, and composition of forest stands and the ecosystem services they provide.

Reanalysis of the 2000 Rift Valley fever outbreak in Southwestern Arabia.

The first documented Rift Valley hemorrhagic fever outbreak in the Arabian Peninsula occurred in northwestern Yemen and southwestern Saudi Arabia from August 2000 to September 2001. This Rift Valley fever outbreak is unique because the virus was introduced into Arabia during or after the 1997-1998 East African outbreak and before August 2000, either by wind-blown infected mosquitos or by infected animals, both from East Africa. A wet period from August 2000 into 2001 resulted in a large number of amplification vector mosquitoes, these mosquitos fed on infected animals, and the outbreak occurred. More than 1,500 people were diagnosed with the disease, at least 215 died, and widespread losses of domestic animals were reported. Using a combination of satellite data products, including 2 x 2 m digital elevation images derived from commercial satellite data, we show rainfall and potential areas of inundation or water impoundment were favorable for the 2000 outbreak. However, favorable conditions for subsequent outbreaks were present in 2007 and 2013, and very favorable conditions were also present in 2016-2018. The lack of subsequent Rift Valley fever outbreaks in this area suggests that Rift Valley fever has not been established in mosquito species in Southwest Arabia, or that strict animal import inspection and quarantine procedures, medical and veterinary surveillance, and mosquito control efforts put in place in Saudi Arabia following the 2000 outbreak have been successful. Any area with Rift Valley fever amplification vector mosquitos present is a potential outbreak area unless strict animal import inspection and quarantine proceedures are in place.

Divergent shrub-cover responses driven by climate, wildfire, and permafrost interactions in Arctic tundra ecosystems.

The expansion of shrubs across the Arctic tundra may fundamentally modify land-atmosphere interactions. However, it remains unclear how shrub expansion pattern is linked with key environmental drivers, such as climate change and fire disturbance. Here we used 40+years of high-resolution (~1.0m) aerial and satellite imagery to estimate shrub-cover change in 114 study sites across four burned and unburned upland (ice-poor) and lowland (ice-rich) tundra ecosystems in northern Alaska. Validated with data from four additional upland and lowland tundra fires, our results reveal that summer precipitation was the most important climatic driver (r=0.67, p<0.001), responsible for 30.8% of shrub expansion in the upland tundra between 1971 and 2016. Shrub expansion in the uplands was largely enhanced by wildfire (p<0.001) and it exhibited positive correlation with fire severity (r=0.83, p<0.001). Three decades after fire disturbance, the upland shrub cover increased by 1077.2±83.6m2 ha-1 , ~7 times the amount identified in adjacent unburned upland tundra (155.1±55.4m2 ha-1 ). In contrast, shrub cover markedly decreased in lowland tundra after fire disturbance, which triggered thermokarst-associated water impounding and resulted in 52.4% loss of shrub cover over three decades. No correlation was found between lowland shrub cover with fire severity (r=0.01). Mean summer air temperature (MSAT) was the principal factor driving lowland shrub-cover dynamics between 1951 and 2007. Warmer MSAT facilitated shrub expansion in unburned lowlands (r=0.78, p<0.001), but accelerated shrub-cover losses in burned lowlands (r=-0.82, p<0.001). These results highlight divergent pathways of shrub-cover responses to fire disturbance and climate change, depending on near-surface permafrost and drainage conditions. Our study offers new insights into the land-atmosphere interactions as climate warming and burning intensify in high latitudes.

Lessons from the Case History of a Massive Landslide Dam

A massive landslide created a natural dam on two tributaries of Jhelum River near the town of Hattian Bala in Kashmir in October 2005. The landslide was triggered by a 7.6 Mw earthquake. The resulting unconsolidated dam and water impoundment upstream carried hazard potential of downstream damage to both infrastructure and population due to potential flooding caused by its breach. Comprehensive investigations and monitoring were implemented to analyse dam stability. Fresh topographic profiles were generated. Samples of the matrix materials were utilized in the laboratory investigations including grain-size analysis, laboratory electrical resistivity and permeability tests at varying densities and degrees of saturation, and sediment concentration assessment in the seepage discharge. A noninvasive geophysical method was employed together with new topographic information to develop transient subsurface pictures and to assess the advancement of seepage fronts within the dam body. Internal erosion/filtering potential of the matrix material was assessed by comparing grain size distributions with those of the earlier failed dams. Upstream inflows, downstream discharges, daily precipitation, and lake levels monitored during the study period were utilized in hydrological data analysis in an attempt to assess the potential seepage volume. A combination of empirical, analytical, and numerical methods and simulations, together with laboratory and field investigations, led to the interpretations regarding short- and long-term stability of the dam. This paper highlights alternative methods of investigation employed differently from those used by other national and international agencies in analysing the failure potential of this natural dam. It offers lessons learned from a case history that can be beneficial in future evaluation of seepage-induced failure of similar natural features.

A huge flood in the Fraser River valley, British Columbia, near the Pleistocene Termination

Near the Pleistocene Termination, a glacier-dammed lake in central British Columbia suddenly drained to the south along the Fraser River valley. Floodwater travelled 330 km down the valley to Hope, British Columbia, and from there to the west into the Salish Sea near Vancouver. The flood was caused by the failure of an ice dam formed by the terminus of glaciers flowing from the central Coast Mountains across the British Columbia Interior Plateau. The ice dam impounded several hundred cubic kilometres of water to a maximum elevation of about 810 m asl (above sea level); at its maximum, the lake at the ice dam was over 250 m deep. Geomorphic and sedimentary evidence for the flood includes streamlined boulder-strewn bars, gravel dune fields, and terraces sloping up Fraser and lowermost Thompson valleys, opposite the present direction of river flow. The gravel bars and flood terraces are underlain by sheets of massive to poorly sorted gravel containing large boulders and rip-up clasts of silt and till. Shortly after the flood, a landslide near the northern margin of the former glacier dam impounded water to an elevation of about 550 m asl. This lake emptied due to overflow and incision of the landslide dam. The outburst flood from glacial Lake Fraser and the subsequent draining of the landslide-dammed lake deeply incised the older sediment fill in Fraser Valley and transported much of this sediment into the proto-Salish Sea west of Vancouver, British Columbia and Bellingham, Washington. TCN ages on flood-transported boulders at three localities along the flood path agree with radiocarbon ages on inferred flood layers in ODP cores collected from Saanich Inlet, a fiord on southern Vancouver Island, 80 km south-southwest of Vancouver.

Food selectivity and reproductive biology of small indigenous fish Indian river shad, Gudusia chapra (Hamilton, 1822) in a large tropical reservoir.

Assessment of life history strategies of economically important small indigenous fishes (SIF) which are rich in nutritive values is essential and imperative to artisanal and subsistence small-scale inland fisheries of Indian tropical reservoirs. The present investigation aims to estimate the food selectivity in juveniles and adults, reproductive traits such as sexual maturity, gonadosomatic index, ova diameter, and fecundity of Gudusia chapra from a large impounded ecosystem of India. A total of 668 (Juvenile 129, adult 539) specimens, 37 to 142mm standard length and 0.89-25.68g body weight were collected during October 2014-September 2015. The qualitative estimation of the stomach contents revealed herbi-omnivorous feeding behavior of fish. The mean relative gut length (mRGL) of the species was 1.557 ± 0.024 in juveniles and 1.154 ± 0.012 in adults. The sex ratio was 1:1.30 with dominance of females in the population though insignificant. The total length at which 50% individual attain maturity (TL50) was estimated as 80.50mmbased on the logistic curve. The absolute fecundity of the individuals ranged from 749 to15044, and ova diameter ranged from 0.10-2.00mm. The gonadal indices (GSI, MGSI, and DI) indicated that spawning extended throughout the year with peak reproductive activity in October, March-April, and July (mean absolute fecundity ranged from 4000 to 6000). The present study characterized biological and reproductive traits of G. chapra from a large reservoir ecosystem and demonstrated a new trend of reproductive pattern which will serve as benchmark data for future assessment and management planning of this species in impounded waters. The study also suggested some specific management measures for sustainable exploitation and conservation of small indigenous species.