Low Flow Years Research Articles

Prediction of Low Flow Years in the Upstream of Zhang River Based on Improved Gray Model

A reasonable prediction of low flow years in a region in the future so as to make deployment in advance is related to the stability of the region. This paper established conventional GM (1,1) model and improved GM (1,1) model based on grey system theory to predict low flow years in the upstream of Zhang River which has gray characteristics so as to avoid risks, improve spatial and temporal allocation of water resources and promote sustainable development of the basin. The research shows that improved GM (1,1) model which can improve the smoothness of the original data series provides a more accurate prediction than conventional GM (1,1) model by using the example of Zhuozhang River tributary in the Upstream of Zhang River.

The Impact of Low Flow on Riverine Food Webs in South-Central Newfoundland

Low-flow events can reduce food availability and decrease the feeding niche of consumers within rivers. Stable carbon (δ13C) and nitrogen (δ15N) isotope and stomach content analyses were employed to evaluate resource use and overlap between fish species in a natural and regulated river in normal and low-flow years, with the use of multiple methodological approaches providing the best means of understanding short-term and long-term observations on fish feeding and resource overlap under changing flow conditions. Diet analyses generally indicated significant inter-specific differences in the diets of key fish species within rivers and similarities in resource use between rivers. In comparison with fish from the natural river, fish from the regulated river had lower and less inter-annually variable δ13C values. In the natural river, there was a significant reduction and increase, respectively, in δ13C and δ15N variation in the low-flow year. Intra-annual or inter-annual differences in trophic niche area were not apparent in the regulated river, whereas within the natural river, intra-annual and inter-annual differences in trophic niche were found. Resource overlap between key fish species was also higher in the low-flow year and lower in the spring and higher in the summer as a result of differences in flow. Resource overlap was also higher between rivers in the low-flow year. High resource overlap between rivers during decreased summer flow indicates a strong effect of flow on river organisms, where both fish and their invertebrate prey resources are concerned. Copyright © 2014 John Wiley & Sons, Ltd.

Impact of the Cascaded Reservoirs and the Tributaries Confluence on the Eco-Hydrology of the Reserve in the Upper Reaches of Yangtze River

For studying the impacts of the tributaries confluence on the hydrological processes in the downstream reaches of the four cascaded reservoirs in the downstream of Jinshajiang River, this paper simulated the daily discharge at the outlet of the cascaded reservoirs and along the reserve mainstream in typical years with the operation programming of the reserve and MIKE11 hydrodynamic model, and eco-hydrology indicators were selected and calculated by IHA to quantify the hydrology process. The result showed that at Xiangjiaba Gauge Station discharge on April and May increased by about 100%, the discharge in low flow year decreased by 50% and the timing of annual 1-day minimum discharge has significantly alteration. The confluence of Minjiang River could effectively mitigate the impacts of the cascaded reservoirs on eco-hydrology of the downstream of the confluence, but the mitigation of others three tributaries were not significant. Moreover the pre-flood high flow in the downstream of the Minjiang River confluence increased by 50%, and other indicators alteration were not significant.

Summer phytoplankton nutrient limitation in Maumee Bay of Lake Erie during high-flow and low-flow years

Algal production in Maumee Bay in western Lake Erie is highly affected by inputs of nitrogen (N) and phosphorus (P) from the Maumee River, which drains predominantly agricultural lands, leading to the formation of cyanobacterial blooms. In a 3-year study, precipitation and discharge ranged from relatively low (2012) to relatively high (2011) with corresponding changes in the size of the cyanobacterial bloom. This study aimed to quantify the relation between river discharge and algal nutrient limitation in Maumee Bay. During the summer growing seasons, 20 nutrient enrichment bioassays were performed to determine which nutrient (P or N) might limit phytoplankton growth; and ambient N and P concentrations were monitored. The bioassays suggested that phytoplankton growth shifted from P-limited to N-limited during summer of the low and intermediate discharge years (2012 and 2010, respectively), whereas during the high discharge year (2011) phytoplankton were nutrient-replete before becoming N-limited. Phosphorus-replete growth during the high discharge year likely was due to high P loads from the river and dissolved P concentrations greater than 1μmol/L. Symptoms of N-limited growth occurred during August and September in all three years and during July of 2012 when NO3− plus NH4+ concentration was less than 7.29μmol/L suggesting low or no correspondence between N-limitation and size of the cyanobacterial bloom. Occurrence of a relatively small cyanobacterial bloom in 2012 following the record-breaking bloom in 2011 suggests the possibility of fast-reversal of eutrophication in Maumee Bay if P loading from the watershed could be decreased.

Nitrate loss in Saylorville Lake reservoir in Iowa

Few studies have quantified nitrate-nitrogen reductions in rivers flowing through large flood control reservoirs despite their potential role in helping to meet nitrate-N load reduction targets. In this study, we evaluated a 26-year record of nitrate-N monitoring in Saylorville Lake reservoir that impounds the Des Moines River in central Iowa to estimate the annual mass of nitrate-N removed and evaluate controls on inter-annual patterns of nitrate-N removal rates. Results from mass balance calculations indicate a nitrate mass loss of 4.9% over the 26 year period from 1986 through 2011. The annual percent nitrate mass removed is related to hydraulic loading rate with low flow years having longer retention times removing a significantly greater percentage of nitrate than is removed during high flow years with low retention times. Average annual residence times varied from 3.5 to 74 days with a 26 year average of 9.7 days. Nitrate removal results for Saylorville Lake agree well with published work for several other reservoirs which together encompass a broad range of nitrate removal rates. Combining data from Saylorville Lake with other published studies, a relationship between nitrate-N removal rate and hydraulic loading rate was developed resulting in a predictive equation with a model R2 = 0.92.

Sediment Transport and its Effect on Navigation in Long Tailrace of Hydropower Station

Using long tailrace channel to navigate is a complex development way which has a common channel for navigation and tailrace. It is gradually tried to use in the Angu hydropower station and Shawan hydropower station of the Dahu River. So the flow and sediment movements are the key and decisive factors for navigation safety. Some achievements have been obtained about the influence of unsteady flow to navigation in tailrace channel. But it is very few to study that of sediment movement. Use the Angu hydropower station as an example, sediment movement is studied in long tailrace channel. Firstly, sediment sources are analyzed by measured data. Secondly, a two-dimensional sediment model and the experience formula are also used to simulate the transport of sediments. The transports of suspended load and bed load are studied with different operation of the hydropower station. Finally, with the typical series of 20 years, which includes high flow year, mean flow year and low flow year, riverbed deformation is predicted in the mooring area, the tailrace channel and its outlet. And the effect on navigation is analyzed. The results show that sediment sources are dominated by the local sediment. The deposition in the tailrace channel is not large and has little influence to navigation safety. A small amount of dredging can meet the needs of maintenance. The research results are helpful to the design and operation of long tailrace channel.

Effect of Longyangxia Reservoir on the Variation of Water and Sediment

Longyangxia reservoir is the key project for the upper reaches of the Yellow River by possessing the interannual regulation capability. This paper analyzes the runoff sediment characteristics since the operation of the reservoir on the basis of the hydrological data before and after the operation of Longyangxia reservoir. The study result indicates that the variation characteristics of water and sediment after the operation of the reservoir mainly include sharply-reduced peak discharge, varied annual runoff distributions, reduced annual runoff coefficient of variation, obviously-reduced quantity of sediment, varied sediment runoff relation; the operation characteristics namely annual storage in flood period, level period discharge high-flow year water storage and low-flow year water supplement of Longyangxia reservoir are the key affecting factors for the variation of water and sediment.

Going with the Flow: Spatial Distributions of Juvenile Coho Salmon Track an Annually Shifting Mosaic of Water Temperature

A critical challenge for ecologists is to understand the functional significance of habitat heterogeneity and connectivity for mobile animals. Here, we explore how a thermo-regulating fish responds to annual variation in the spatial patterning of thermal and trophic resources. In a third-order stream in coastal Alaska, juvenile coho salmon forage on sockeye salmon eggs at night in cold water and then move to warmer water to increase their digestive capacity. We mapped the spatial distributions of water temperature, juvenile coho salmon, and spawning sockeye salmon across a 5-year period during which summer discharge varied by greater than fivefold. In low flow years, warm water (9–12°C) was only available in thalweg (that is, main-channel) habitat at least approximately 400 m upstream of the cooler habitat (3–7°C) where sockeye salmon spawned. In high flow years, the entire stream thalweg was isothermal at 7–8°C, but inundated off-channel areas generated warm habitats (9–12°C) laterally adjacent to the downstream regions where sockeye salmon spawned. The daytime spatial distribution of juvenile coho salmon shifted from headwater thalweg habitats in low flow years, to downstream off-channel habitats in high flow years. In all years, the majority of juvenile coho salmon sampled during the daytime were found in warm habitat units without sockeye salmon present, yet they exhibited diet contents comprised virtually entirely of sockeye salmon eggs. Thus, thermoregulatory movements by coho salmon were able to track an annually shifting mosaic of water temperature. Our results demonstrate how the spatial habitat heterogeneity and connectivity of intact floodplains can in turn buffer aquatic organisms from high levels of temporal variation in habitat conditions and resource abundance.

Effects of water discharge on fledging time, growth, and survival of piping plovers on the Missouri River

AbstractRiver flow management and modification is a global issue, and its effects on river‐dependent organisms are pervasive. Flow modification can directly affect avian species through mortality or habitat loss, but less is known about indirect and sublethal effects of flow modification on reproductive output in these species. Young birds are more vulnerable to predation between hatching and fledging than after flight is achieved, but tradeoffs must be made to balance growth and survival. Predation pressure appears to be a significant factor affecting the time to fledging in altricial birds, but less is known about this threat for precocial birds. Birds reaching fledging earlier should have greater rates of survival to migration because their predator escape repertoire includes flight at an earlier age. We evaluated the effect of varying outflows from the Gavins Point Dam on the growth, age at fledging, and survival of piping plover (Charadrius melodus) chicks on the Missouri River (2006–2009). The study was characterized by 2 relatively high flow years (2006 and 2009) and 2 relatively low flow years (2007 and 2008). We used success rate in recapturing chicks in capture–mark–recapture models as an index for fledging. We attempted to recapture all chicks (n = 1,099) by hand every 3–4 days throughout the season to acquire morphological measurements. Models indicated that as flows from the dam increased, age at fledging increased. We also found that increasing flows were associated with decreasing daily survival rates (βflow = −2.401, 95% CI: −4.351 to −0.452). Flow was also negatively related to chick mass gain, but we found less evidence for an effect on wing‐chord length. Increased flows covered wet‐substrate foraging habitat, and likely affected plover reproductive output directly through chick survival and indirectly through decreased growth and increased fledging times. © The Wildlife Society, 2013

Model development for prediction and mitigation of dissolved oxygen sags in the Athabasca River, Canada

Northern rivers exposed to high biochemical oxygen demand (BOD) loads are prone to dissolved oxygen (DO) sags in winter due to re-aeration occurring within limited open water leads. Additionally, photosynthesis is reduced by decreased daylight hours, inability of solar radiation to pass through ice, and slower algal growth in winter. The low volumetric flow decreases point-source dilution while their travel time increases. The Athabasca River in Alberta, Canada, has experienced these sags which may affect the aquatic ecosystem. A water quality model for an 800km reach of this river was customized, calibrated, and validated specifically for DO and the factors that determine its concentration. After validation, the model was used to assess the assimilative capacity of the river and mitigation measures that could be deployed. The model reproduced the surface elevation and water temperature for the seven years simulated with mean absolute errors of <15cm and <0.9°C respectively. The ice cover was adequately predicted for all seven winters, and the simulation of nutrients and phytoplankton primary productivity were satisfactory. The DO concentration was very sensitive to the sediment oxygen demand (SOD), which represented about 50% of the DO sink in winter. The DO calibration was improved by implementing an annual SOD based on the BOD load. The model was used to estimate the capacity of the river to assimilate BOD loads in order to maintain a DO concentration of 7mg/L, which represents the chronic provincial guideline plus a buffer of 0.5mg/L. The results revealed the maximum assimilative BOD load of 8.9ton/day at average flow conditions, which is lower than the maximum permitted load. In addition, the model predicted a minimum assimilative flow of about 52m3/s at average BOD load. Climate change scenarios could increase the frequency of this low flow. A three-level warning-system is proposed to manage the BOD load proactively at different river discharges. Other mitigation options were explored such as upgrading the wastewater treatment of the major BOD point source and oxygen injection in the effluents. The model can be used as a management tool with updated SOD values to forecast the DO in low flow years and evaluate mitigation measures. As well, the methodology presented here can be applied to manage other ice-covered rivers.

Hydrologic linkages between a climate oscillation, river flows, growth, and wood Δ13C of male and female cottonwood trees

To investigate climatic influence on floodplain trees, we analysed interannual correspondences between the Pacific Decadal Oscillation (PDO), river and groundwater hydrology, and growth and wood (13)C discrimination (Δ(13)C) of narrowleaf cottonwoods (Populus angustifolia) in a semi-arid prairie region. From the Rocky Mountain headwaters, river discharge (Q) was coordinated with the PDO (1910-2008: r(2) = 0.46); this pattern extended to the prairie and was amplified by water withdrawal for irrigation. Floodplain groundwater depth was correlated with river stage (r(2) = 0.96), and the cottonwood trunk basal area growth was coordinated with current- and prior-year Q (1992-2008: r(2) = 0.51), increasing in the mid-1990s, and decreasing in 2000 and 2001. Annual Δ(13)C decreased during low-flow years, especially in trees that were higher or further from the river, suggesting drought stress and stomatal closure, and male trees were more responsive than females (-0.86 versus -0.43‰). With subsequently increased flows, Δ(13)C increased and growth recovered. This demonstrated the linkages between hydroclimatic variation and cottonwood ecophysiology, and we conclude that cottonwoods will be vulnerable to drought from declining river flows due to water withdrawal and climate change. Trees further from the river could be especially affected, leading to narrowing of floodplain forests along some rivers.

Future runoff from a partly glacierized watershed in Central Switzerland: A two-model approach

We present a comprehensive hydrological modeling study in the drainage area of a hydropower reservoir in central Switzerland. To investigate the response of this 95km2 alpine watershed to a changing climate, we used both a conceptual and a physically based hydrological model approach. The multi-model approach enabled detailed insights into the uncertainties associated with model projections of future runoff based on climate scenarios. Both hydrological models consistently predicted changes of the seasonal runoff dynamics, including the timing of snowmelt and peak-flow in summer as well as the future spread between high and low flow years. However the models disagreed regarding the evolution of glacier melt rates thus leading to a considerable difference in predicted annual runoff figures. The findings suggest that snow-glacier feedbacks require particular attention when predicting future runoff from glacio-nival watersheds.

Predicted macroinvertebrate response to water diversion from a montane stream using two-dimensional hydrodynamic models and zero flow approximation

We used two-dimensional hydrodynamic models for the assessment of water diversion effects on benthic macroinvertebrates and associated habitat in a montane stream in Yosemite National Park, Sierra Nevada Mountains, CA, USA. We sampled the macroinvertebrate assemblage via Surber sampling, recorded detailed measurements of bed topography and flow, and coupled a two-dimensional hydrodynamic model with macroinvertebrate indicators to assess habitat across a range of low flows in 2010 and representative past years. We also made zero flow approximations to assess response of fauna to extreme conditions. The fauna of this montane reach had a higher percentage of Ephemeroptera, Plecoptera, and Trichoptera (%EPT) than might be expected given the relatively low faunal diversity of the study reach. The modeled responses of wetted area and area-weighted macroinvertebrate metrics to decreasing discharge indicated precipitous declines in metrics as flows approached zero. Changes in area-weighted metrics closely approximated patterns observed for wetted area, i.e., area-weighted invertebrate metrics contributed relatively little additional information above that yielded by wetted area alone. Loss of habitat area in this montane stream appears to be a greater threat than reductions in velocity and depth or changes in substrate, and the modeled patterns observed across years support this conclusion. Our models suggest that step function losses of wetted area may begin when discharge in the Merced falls to 0.02m3/s; proportionally reducing diversions when this threshold is reached will likely reduce impacts in low flow years.

Trend of Annual Runoff for Major Rivers in China under Climate Change

In order to understand the variation of hydrological regime for major rivers in China under climate change since 1950, the series of annual runoff for those rivers were analyzed by using several methods, including M-K method, accumulation curve method, F & T test, and anomaly analysis method. The results of this study showed that the annual runoff for only a part of those rivers took on a significant trend under climate change. Additionally, the occurring frequency of both extremely low-flow years and continuous low-flow years for most of those rivers increased after 1980.

Peculiarities of the Upper Amu Darya Basin Rivers Zonal Runoff in Lowwater and High-water Years

Some peculiarities of the rivers’zonal runoff during high-water and low-water years for homogeneous hydrologic regions of the upper Amu Darya River basin have been studied. By solving the ill-posed inverse problem, the values of the zonal runoff for spring and summer periods were estimated for the selected years with high and low water. Glacial component is shown to play a larger role in the runoff during low flow years.

Tree ring-based annual streamflow reconstruction for the Heihe River in arid northwestern China from ad 575 and its implications for water resource management

We developed two tree ring-width chronologies (Qilian juniper, Sabina przewalskii Kom.) for the inland Heihe River Basin in arid northwest China using a large number of tree-ring samples (217 samples/92 trees) with accurate information about pith offsets based on Regional Curve Standardization (RCS) and standard dendrochronological (STD) methodologies. Two 1422-year reconstructions of annual (August–July) streamflow for the upstream region of the Heihe River are presented. The STD and RCS reconstructions account for 53.4% and 57.2% of the actual streamflow variance during the period 1958–2006, respectively. Both reconstructions display considerable low frequency (multidecadal to multicentury) fluctuations, although the RCS based reconstruction is superior to the STD based reconstruction for retention of low-frequency trends. Low-flow years in ad 818–852, 1112–1196, 1453–1495 and 1680–1710, and high-flow periods in ad 868–1000, 1056–1094, 1228–1271, 1327–1440, 1510–1583 and 1877–2006 are detected in both reconstructions. Both the STD and the RCS reconstructions testify to the fact that the 20th century witnessed intensified pluvial conditions in the upstream region of the Heihe River in the context of the last 1500 years. The streamflow reconstructions are anticipated to be useful to water resource planning and management for the Heihe River Basin in arid northwestern China.

MANAGING THE FLOOD PULSE FOR OPTIMAL FISHERIES PRODUCTION IN THE ATCHAFALAYA RIVER BASIN, LOUISIANA (USA)

ABSTRACTThe Atchafalaya River Basin in south‐central Louisiana (USA) comprises the largest contiguous river–floodplain swamp in North America and functions as a distributary for the Mississippi River to the Gulf of Mexico. We assessed the impact of the annual flood pulse on fisheries production at a basin‐wide scale. We modelled flood duration (days/year Butte LaRose gauge height &gt;3.6 m) and magnitude (mean daily gauge height) against long term (1987–2009) fishery‐independent and fishery‐dependent data on largemouth bass (Micropterus salmoides), crappie (Pomoxis spp.), blue catfish (Ictalurus furcatus), buffalofish (Ictiobus spp.), gizzard shad (Dorosoma cepedianum) and crayfish (Procambarus spp.). When the Atchafalaya River at Butte LaRose is at flood stage (≥ 3.6 m gauge height) for approximately 121–157 days/year, then annual relative abundances of largemouth bass, crappie, blue catfish and buffalofish are optimized during the fall (October–December). In contrast to the tenets of the flood pulse concept, gizzard shad abundance was optimized during low flow years, when flood duration is ≤10 days/year. Annual proportion of age‐1 largemouth bass was associated positively with flow magnitude during the previous year, whereas proportions of age‐2 largemouth bass and crappie were associated positively with flood magnitude 2 years prior to the fish sample. Results for commercial production metrics were ambiguous. Crayfish catches were associated positively with flood magnitude and duration, whereas gizzard shad landings peaked at a relatively small flood magnitude level and were not related to flood duration. Blue catfish and buffalofish annual landings were not influenced by the annual flood pulse. The annual flood pulse can be managed to optimize the availability of recreational (largemouth bass and crappie) and some commercial fisheries resources (blue catfish and crayfish). We estimate that a minimum discharge of 8807 m3 s−1 is required at the river's source for approximately 4–5 months during the winter–spring months to optimize fisheries production. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Stratigraphic, sedimentologic, and dendrogeomorphic analyses of rapid floodplain formation along the Rio Grande in Big Bend National Park, Texas

The channel of the lower Rio Grande in the Big Bend region rapidly narrows during years of low mean and peak flow. We conducted stratigraphic, sedimentologic, and dendrogeomorphic analyses within two long floodplain trenches to precisely reconstruct the timing and processes of recent floodplain formation. We show that the channel of the Rio Grande narrowed through the oblique and vertical accretion of inset floodplains following channel-widening floods in 1978 and 1990–1991. Vertical accretion occurred at high rates, ranging from 16 to 35 cm/yr. Dendrogeomorphic analyses show that the onset of channel narrowing occurred during low-flow years when channel bars obliquely and vertically accreted fine sediment. This initial stage of accretion occurred by both bed-load and suspended-load deposition within the active channel. Vegetation became established on top of these fine-grained deposits during years of low peak flow and stabilized these developing surfaces. Subsequent deposition by moderate floods (between 1.5 and 7 yr recurrence intervals) caused additional accretion at rapid rates. Suspended-sediment deposition was dominant in the upper deposits, resulting in the formation of natural levees at the channel margins and the deposition of horizontally bedded, fining-upward deposits in the floodplain trough. Overall, channel narrowing and floodplain formation occurred through an evolution from active-channel to floodplain depositional processes. High-resolution dendrogeomorphic analyses provide the ability to specifically correlate the flow record to the onset of narrowing, the establishment of riparian vegetation, the formation of natural levees, and ultimately, the conversion of portions of the active channel to floodplains.

Impact analysis of the Three-Gorges Project on the spawning of Chinese sturgeon Acipenser sinensis

Summary The spawning run of adult Acipenser sinensis was blocked by the Gezhouba Dam in 1982 and the flow line was altered again in October and November, when during the spawning period the Three Gorges Project (TGP) started to fill the reservoir with water. This alteration of river flow may affect spawning of A. sinensis. By comparing historical river flow records at spawning dates and outflow at the design year from TGP, we found that A. sinensis spawning in the Yangtze river took mostly place below the Gezhouba Dam on the flood receding period, and discharge volumes of about 7110 m3 s−1 were at the minimum for the spawning of A. sinensis. The Three Gorges reservoir operation as designed would satisfy the spawning flows for A. sinensis except in low-flow years. Once low flow years occur, an adaptive operational procedure should be taken to meet the A. sinensis spawning requirements for hydrodynamics. This can be achieved by impounding water early on and taking rapid responses to meet the flow at the spawning time of A. sinensis.

Spatially variable response of native fish assemblages to discharge, predators and habitat characteristics in an arid-land river

Summary 1. Fish assemblages and habitats were sampled annually at fixed sites in three tributaries of the Gila River catchment over a 21-year span that included prolonged low- and high-flow periods. Model selection was used to evaluate responses of seven native fishes with variable ecological traits (four small-bodied cyprinids, one large-bodied cyprinid, and two large-bodied catostomids) to mean annual discharge and predacious non-native fishes across the three sites. We also compared habitat use and overlap of native and non-native fishes to identify potential for negative interactions among species. 2. Assemblage structure (species abundance and richness) and recruitment of native species was strongly and primarily affected by mean annual discharge and secondarily by location and densities of non-native predators (mainly the centrarchid Micropterus dolomieui). 3. Densities of age-0 catostomids and small-bodied cyprinids were positively associated with discharge, and this pattern was strongest in the tributary with the lowest densities of non-native predators. Absence or extreme low abundance of natives during low-flow years was most pronounced at the sites where non-native predators were comparatively common. Densities of adults of large-bodied native species also varied by site, but often were positively associated with densities of non-native predators. 4. Spatially variable responses of native fish assemblages indicated that the persistence of native fishes could be jeopardized if key habitats were lost or flow regimes unnaturally altered, particularly during low-flow conditions when recruitment of native fishes is low and predation by non-natives is high. Large-bodied species may be less vulnerable to multiple years of poor conditions because adults are able to avoid predation by non-natives and thus can rely on occasional high discharge years for successful recruitment. 5. As in other arid-land streams, native fish assemblages of the Gila River Basin continue to decline. Our results indicate that conservation requires specific knowledge and consideration of physical influences as well as life-history attributes of native and non-native fishes.