Floodplain Water Level Research Articles

Surface water quality in Amazonian Floodplain Lakes, data set of the Lago Grande de Curuai Floodplain Lake, Pará‐Brazil

AbstractBetween 2013 and 2017, we carried out nine field missions in the Lago Grande de Curuai floodplain, located in Pará state – North of Brazil – to collect samples for monitoring surface water quality. This site separated from the river by a narrow bank is composed of a network of channels and shallow lakes, a morphology shared by the floodplains of the lower Amazon. A multiparameter probe was used in situ to measure electrical conductivity, temperature, pH, dissolved oxygen, chlorophyll, turbidity, depth and a Secchi disk to estimate transparency. Water grab samples were analysed for suspended material, alkalinity, humic acid, phosphorus, nitrogen, carbon and chlorophyll. Sampling stations were distributed over the seven larger lakes in the floodplain and sampled at different periods of the hydrological cycle. The number of samples varied with the floodplain water level, with a minimum of 25 samples for each field visit. This data set is a collection of water quality data to assist in the limnological or biogeochemical studies of surface waters in Amazonian floodplain lakes, and the product of successive French‐Brazilian projects: (1) the Clim‐FABIAM ‘Climate changes and Floodplain lake biodiversity in the Amazon Basin: how to cope and help the ecological and economic sustainability’ funded by the French Foundation for biodiversity research (FRB), (2) the project Bloom‐ALERT –‘Environmental sensitivity and population health vulnerability to cyanobacteria in the Amazon: towards shared indicators’ funded by the French‐Brazilian research program GUYAMAZON 2014, and the project (3) ‘Ecossistemas das várzeas e biodiversidade: Impactos das mudanças ambientais e climáticas considerando cenários de desenvolvimento sustentáveis’ (Project number 490634/2013‐3) funded by the Brazilian National scientific Research Council CNPq.

Crevasse splay morphodynamics near a non-vegetated, ephemeral river terminus: Insights from process-based modelling

Crevasse splays generate subtle local relief and contribute to fluvial basin sedimentary filling but controls on splay development along dryland rivers remain poorly understood owing to limited field, laboratory, and numerical modelling studies. Based on previously-acquired field data and new remote sensing observations of splay morphology and sedimentology (e.g. slope, width, length, grain size) and flooding characteristics (e.g. discharge, water depth and extent) near the terminus of the non-vegetated, ephemeral Río Colorado on the southeastern margin of Salar de Uyuni, Bolivia, we undertake process-based modelling using Delft3D to isolate the role of hydrological controls on crevasse splay morphodynamics. Holding the potential sediment supply constant, we focus on the role of discharge (outflow from trunk channel to crevasse channel during rising stage), floodplain water levels, and backflow (reflux to the trunk channel during falling stage). Using nine different model runs, each with 10 simulated flood cycles, we show that the processes associated with these hydrological controls result in various outcomes, from short crevasse splay channels that may bifurcate and develop depositional bars to longer splays with one primary channel that mainly transfers sediment across the floodplain. Results reveal that increases in flood discharge lead to more rapid splay sedimentation and stabilization of a single crevasse channel. Increases in floodplain water level lead to shorter but wider splays and facilitate the formation of multiple stable crevasse channels. High floodplain water levels probably restrict splay length owing to deceleration of outflow as floodplain water is encountered, but separate crevasse channels may form downstream as backflow breaches the trunk channel levee during falling stage. These findings support and extend previous observations from the Río Colorado and other dryland rivers worldwide. Future modelling studies that consider a wider range of hydrological, sedimentological, and floodplain topographic conditions will help develop more comprehensive numerical models of splay development. A combination of insights from field, laboratory experimentation, remote sensing and modelling will improve knowledge of the cascades of channel-floodplain dynamics that characterise many dryland endorheic basins.

Embankment lowering and natural self-recovery improves river-floodplain hydro-geomorphic connectivity of a gravel bed river

Floodplain reconnection can potentially improve the hydrogeomorphology of river corridors and attenuate flood peaks. However, empirical evidence of its effectiveness – needed to inform future restoration – is limited. A 70 m long flood embankment was lowered on the upper River Dee, a medium sized gravel bed river in north-east Scotland to reconnect a backwater and floodplain. Comparison of two years pre- and three years of post-restoration hydro-geomorphic monitoring, shows the lowering and subsequent adjustment, assisted by several floods including a <1% annual exceedance probability event, have altered the morphology and hydrological dynamics. Channel aggradation of up to 1 m occurred. Erosion of the bank by up to 0.41 m in depth and deposition of gravel or sand within the backwater and the floodplain were the dominant geomorphic responses elsewhere. The channel adjustment, unexpected in the restoration design, improved hydrological connectivity with the floodplain; annual median water table levels were on average 0.037–0.089 m higher post-restoration although the correlation between river discharge and floodplain water levels did not change. Based on 1D modelling, the threshold river discharge for backwater connection decreased by 55% from 93 m3 s−1 (discharge exceedance percentile: Q0.4) to 42 m3 s−1 (Q8). Thus, overspill frequency increased. For a given peak discharge, floodplain water levels were higher on average by 0.25 m with a statistically significant difference (Mann Whitney U test: p < 0.05), due to improved hydrological connectivity. The monitoring demonstrates that localised but significant improvement of channel to floodplain hydro-geomorphic connectivity can result from targeted embankment lowering. Such actions could enhance future catchment resilience by improving water storage and biogeochemical processing.

On the Hydrodynamic Behavior of the Changed River–Lake Relationship in a Large Floodplain System, Poyang Lake (China)

Poyang lake floodplains are hydrologically complex and dynamic systems which exhibit dramatic intra-annual wetting and drying. The flow regime of the Yangtze River was previously known to play an important role in affecting Poyang Lake and its extremely productive floodplains (river–lake relationship). The recent severe declines and recessions in the lake are closely linked to the changed river–lake relationship, resulting in significant hydrological, ecological, and economic problems. This study aims to examine the spatiotemporal heterogeneity of the floodplain hydrodynamic behaviors with respect to impacts of the changed river–lake relationship, characterized by the lake water level, inundation area, and inundation duration based on a floodplain hydrodynamic model of Poyang Lake, and to further quantify the severity of dryness recently endured since 2000. Simulation results show that, in general, the current modified river–lake relationship is more likely to affect the hydrological seasonality of the floodplain system since 2000, relative to the flooding and drying cycles during past decades (1953–2000). The present hydrodynamic behaviors suffered significant change due to the greatest interference from the altered river–lake relationship, particularly for the falling period in October. On average, the floodplain water level and inundation duration decreased by 6 m and 12 days during October, respectively. Additionally, the highest monthly shrinkage rate in floodplain inundation shifted from the period of October–November to September–October, with the mean inundation area decreasing by around 50%, demonstrating an advanced and prolonged dry condition. The spatial responses of the hydrodynamics in the low-slope floodplains are most likely to be affected by the dynamic river–lake relationship, as expected. This study assessed the effects of the altered river–lake relationship on the hydrological regime of the Poyang Lake floodplains in terms of spatiotemporal distributions and changing processes for the periodic inundated behavior, which can support the relevant study of the subsequent ecological effects on the wetlands.

Improving flood inundation forecasts through the assimilation of in situ floodplain water level measurements based on alternative observation network configurations

Reliable flood forecasting systems are the prerequisite for proper flood warning systems. Currently, satellite remote sensing (SRS) observations are widely used to improve model forecasts. Although they provide distributed information, they are sometimes unable to satisfy flood modellers’ needs due to low overpass frequencies and high measuring uncertainties. This paper assesses the potential of sparsely distributed, in situ floodplain water level sensors to provide accurate, near-real time flood information as a means to enhance flood predictions. A synthetic twin experiment evaluates the assimilation of different sensor network configurations, designed through time series clustering and Voronoi spacing. With spatio-temporal RMSEs reaching up to 1 cm, the study demonstrates great potential. Adequate sensor placement proved crucial for improved performance. In practice, observation locations should be chosen such that they are located rather close to the river, to increase the likelihood of early flooding and thus acquiring valuable information at an early stage of flooding. Furthermore, high measuring frequencies benefit the simulations, though one should be careful not to overcorrect water levels as these may result in inconsistencies. Lastly, a network size of 5 to 7 observations yields good results, while an increasing number of observations generally diminishes the importance of extra observations. Our findings could greatly contribute to future flood observing systems to either compensate for ungauged areas, or complement current SRS practices.

Seasonal dynamics of terrestrial vertebrate abundance between Amazonian flooded and unflooded forests.

The flood pulse is the main factor structuring and differentiating the ecological communities of Amazonian unflooded (terra firme) and seasonally-flooded (várzea) forests as they require unique adaptations to survive the prolonged annual floods. Therefore, várzea and terra firme forests hammer out a spatio-temporal mosaic of resource availability, which may result in landscape scale seasonal movements of terrestrial vertebrates between adjacent forest types. Yet the lateral movements of terrestrial vertebrates between hydrologically distinct neighbouring forest types exhibiting staggered resource availability remains poorly understood, despite the important implications of this spatial dynamic for the ecology and conservation of forest wildlife. We examined the hypothesis of terrestrial fauna seasonal movements between two adjacent forest types at two contiguous sustainable-use forest reserves in Western Brazilian Amazonia. We used camera trapping data on the overall species richness, composition, and abundance of nine major vertebrate trophic guilds to infer on terrestrial vertebrate movements as a function of seasonal changes in floodplain water level. Species richness differed in neighboring terra firme forests between the high-and low-water phases of the flood pulse and terra firme forests were more species rich than várzea forests. There were clear differences in species composition between both forest types and seasons. Generalized Linear Models showed that water level was the main factor explaining aggregate abundance of all species and three trophic guilds. Our results indicate that the persistence of viable populations of large terrestrial vertebrates adjacent to major Amazonian rivers requires large, well-connected forest landscapes encompassing different forest types to ensure large-scale lateral movements by forest wildlife.

Managed flooding can augment the benefits of natural flooding for native wetland vegetation

Managed flooding is increasingly being used to maintain and restore the ecological values of floodplain wetlands. However, evidence for its effectiveness is sometimes inconsistent and water available for environmental purposes often limited. We experimentally inundated a floodplain wetland (or “billabong”) in late spring by pumping water from its adjacent creek, aiming to promote the native wetland flora and suppress terrestrial exotics. Vegetation was surveyed before (spring) and after (late summer) the managed flood in the experimental billabong and in three control billabongs. Floodplain water levels were continuously monitored. Wet conditions caused two of the control billabongs to also flood, but to a lesser extent than the experimental billabong. We therefore assessed vegetation changes relative to flooding duration. With increasing flooding duration, the cover of wetland vegetation (amphibious and aquatic species) increased and the cover of terrestrial and exotic vegetation decreased, with these effects largest in the deliberately flooded billabong. Flooding durations greater than 20 days generally resulted in increased cover of wetland plants and restricted the growth of terrestrial plants. Reinstatement of more appropriate flooding regimes can thus promote native wetland plants, while suppressing terrestrial exotic species. Our study also provides evidence for the use of modest water allocations to augment the benefits of natural flooding in the maintenance and restoration of native wetland plant communities.

Reconstruction of Ob River, Russia, discharge from ring widths of floodplain trees

The Ob is the third largest Eurasian river supplying heat and freshwater to the Arctic Ocean. These inputs influence water salinity, ice coverage, ocean temperatures and ocean circulation, and ultimately the global climate system. Variability of Ob River flow on long time scales is poorly understood, however, because gaged flow records are short. Eleven tree-ring width chronologies of Pinus sibirica and Larix sibirica are developed from the floodplain of the Lower Ob River, analyzed for hydroclimatic signal and applied as predictors in a regression model to reconstruct 8-month average (December-July) discharge of the Ob River at Salekhard over the interval 1705–2012 (308yrs). Correlation analysis suggests the signal for discharge comes through air temperature: high discharge and floodplain water levels favor cool growing-season air temperature, which limits tree growth for the sampled species at these high latitudes. The reconstruction model (R2=0.31, 1937–2009 calibration period) is strongly supported by cross-validation and analysis of residuals. Correlation of observed with reconstructed discharge improves with smoothing. The long-term reconstruction correlates significantly with a previous Ob River reconstruction from ring widths of trees outside the Ob River floodplain and extends that record by another century. Results suggest that large multi-decadal swings in discharge have occurred at irregular intervals, that variations in the 20th and 21st centuries have been within the envelope of natural variability of the past 3 centuries, and that discharge data for 1937–2009 underestimate both the variability and persistence of discharge in the last 3 centuries. The reconstruction gives ecologists, climatologists and water resource planners a long-term context for assessment of climate change impacts.

Diffusion modeling of recessional flow on central Amazonian floodplains

We present a continuity‐based approach for calculating flow delivered to a main channel from an adjacent floodplain and use the values in a linear diffusion model to generalize fluxes across a floodplain. Using interferometric synthetic aperture radar (SAR) measurements of floodplain water level changes and the continuity equation, we demonstrate that flow rates are not the same throughout Amazonian floodplains. Also, rates of floodplain storage change are found to be least in areas of greatest distance from a main channel which suggests a long residence time. Linear diffusion modeling of floodplain drainage represents the composite behavior of flow through channels, swamps and lakes and provides a simple method of defining storage changes. The key parameter necessary for diffusion modeling is floodplain conductivity which can be constrained by a simple description of floodplain topography and measurements of temporal changes in floodplain water levels.

Linking hydrodynamics, conservation biology, and economics in choosing naturalization alternatives for the Illinois River, USA.

Major investments have been made recently along the Illinois River in habitat rehabilitation and enhancement, stream bank stabilization, and conversion of former agricultural drainage and levee districts back to floodplains. Past efforts included intense site-specific habitat management, such as manipulation of water levels in floodplain lakes to provide feeding and resting habitat for migratory waterfowl; and broad-based programs of financial incentives and technical assistance for landowners to control erosion and provide wildlife habitat. Innovative approaches to recover systemic river functions require decisions in the face of uncertainties, and hydraulic, ecological, and economic models are being developed to aid analysis of alternatives. Early biophysical modeling results indicate that location (for example, distance from dams) can be important to the likely success and cost of naturalization. Economic modeling indicates that impacts that are beneficial at the regional and state scale may be either negative or positive for local communities along the rivers. The analytical tools and multi-disciplinary approaches being developed are relevant to river rehabilitation or naturalization in other developed countries, and also to river conservation in developing countries that wish to sustain natural goods and services while undertaking commercial development.

Water Storage of the Central Amazon Floodplain Measured with GIS and Remote Sensing Imagery

Interferometric processing of a Space Shuttle–based swath of synthetic aperture radar (SAR) data collected over the central Amazon floodplain reveals one-day decreases in water levels ranging from 1 to 11 cm in mid-October 1994. The decreases, plotted in a geographic information system (GIS), do not appear to be related to water-body size. Instead, the drops correlate with distance between measured location and main river channel. Because the flow routes connecting observed water bodies to a river channel are convoluted, stream network extraction algorithms operating within a GIS are ideally suited to identify flow-path distances. High-resolution digital elevation models (DEMs) are not available for the Amazon Basin; instead, extraction algorithms are applied to a basin-wide mosaic of raster-based SAR amplitude data. SAR amplitudes mimic topography with weak radar returns over open water lying in low elevations and strong returns over non-flooded, higher elevations. As flow-path distance increases, there is a general decrease in the floodplain water level drops. This functional relationship is used to extrapolate the swath of interferometrically based observations beyond their ∼15-percent coverage of the central Amazon floodplain. If the extrapolation is correct, the decreases in water levels sum to a storage change of 4,600 m3/s from an area of 11,800 km2 across the floodplain during midrecessional flow. This value is about 30 percent less than the storage change estimates previously derived from flood routing. The difference likely results from the model-based assumption that water-level fluctuations across the floodplain are equivalent to those in the main river channel. The interferometric observations suggest that this equivalence does not appear to be correct for mid-October 1994.

Amazon floodplain water level changes measured with interferometric SIR-C radar

The authors find that interferometric processing of repeat-pass L-HH-band shuttle imaging radar (SIR-C) data reveals centimeter-scale changes in the elevations of water surfaces within flooded vegetation. Because radar pulses reflect specularly from the water surface, interferometric observations of open water are incoherent. However, within flooded forests and inundated shrubs, the L-band radar pulse penetrates the vegetation canopy and follows a double-bounce travel path that includes the water and vegetation-trunk surfaces. In these environments, the returned radar energy and associated phase coherence are both stronger than the surrounding nonflooded terrain, permitting determination of the interferometric phase. Phase errors related to atmospheric water vapor are usually longer in wavelength and spatially distinct from phase signatures related to stage changes in tributaries and floodplain lakes. The interferometrically measured stage decreases match gauge data, providing further verification. Water level changes across 150 m to 2.75 km-wide water bodies containing inundated vegetation can be reliably measured. The authors' results suggest that if future interferometric L-HH-band SAR missions are implemented with short temporal baselines, it is possible to measure the hydrologic response of wetlands and inundated floodplains to changes in mainstem water level.

Soil water storage and groundwater behaviour in a catenary sequence beneath forest in central Amazonia. II. Floodplain water table behaviour and implications for streamflow generation

Abstract. Valley floor groundwater level data collected during the ABRACOS project (Gash et al. 1996), and published streamflow data from small forested catchments in geomorphologically similar areas nearby have been analysed to improve the understanding of the processes of streamflow generation. Early in the wet season, the floodplain water table is typically at 0.8 m depth, or less, and receives only local, vertical recharge. Large storms may create a groundwater ridge beneath the floodplain, temporarily creating a gradient in the direction of the hilislope. Later in the wet season, floodplain water levels are controlled primarily by the discharge of groundwater which maintains the dry season streamflow. The groundwater is recharged by deep drainage from beneath the plateau and slope areas once the dry season soil water deficit has been overcome. In the late wet season, the water level is almost at the floodplain surface and may create seeps on the lower slopes in very wet years. For the period 1966-1989, the recharge was estimated to range from 290 mm to 1601 mm with a mean of 1087 mm. Published data show that baseflow is 91% of annual runoff. Stormflow is generated on the floodplain, and water table recessions after rainfall events show that the runoff response depends on the depth to the water table. These results are from areas with deeply weathered and permeable soils; in areas of Amazonia with shallower soils, the predominant flow generation processes will differ (Elsenbeer and Lack, 1996).

An outline on lateral fish migrations within the Central Delta of the Niger River, Mali

The lateral migration of fishes was studied during one entire flood cycle (1991) in a typical floodplain sector of the Central Delta of Niger at Batamani, Mali. The intensity and temporal course of migrations, as well as the species and size composition of migrants, were found to be correlated with the hydrological regime (river and floodplain water levels, direction and velocity of water flow in a temporary canal). Four different types of migratory patterns were described and their typical representatives indicated. The significant role of the river as a spawning site and that of the flood plain as a nursery for most locally important fishes was also accentuated.

Maintaining numerical stability of flood plain calculations by time increment splitting

An algorithm for simulating flood plain water levels during flood propagation in embanked river systems is presented. The algorithm uses volume conservation to simulate flood plain conditions. It differs from other storage pond algorithms in that it automatically adjusts the time increment used to maintain numerical stability. The time increment adjustment is carried out locally on the flood plain, permitting the main channel solution to proceed, using a time increment suitable for efficient implicit flood routeing calculations. Test results using hypothetical river data are presented

MAINTAINING NUMERICAL STABILITY OF FLOOD PLAIN CALCULATIONS BY TIME INCREMENT SPLITTING.

An algorithm for simulating flood plain water levels during flood propagation in embanked river systems is presented. The algorithm uses volume conservation to simulate flood plain conditions. It d...

Magpie Goose, Anseranas-Semipalmata, Nesting on the Mary River Floodplain, Northern-Territory, Australia - Extent and Frequency of Flooding Losses

Magpie geese, Anseranas semipalmata, nest synchronously in large colonies on the seasonally inundated floodplains of the Northern Territory. Erratically variable wet season rainfalls may cause rises in floodplain water levels that destroy many nests. We describe such an event on the Mary River foodplain in which all of the nests within a monitored study area were drowned. Vulnerability to flooding (as indicated by variation in the depth at which eggs first submerged) varied significantly among vegetation types. Mean rises in water levels causing inundation of eggs varied from 67 cm in nests constructed on a base of Oryza rufipogon to 118 cm on nests constructed on Eleocharis brassii. Nests close to major river channels are more vulnerable to flooding. Analysis of patterns of river level rises since 1959 indicate that such catastrophic nest losses are relatively common, perhaps occurring as often as one year in seven. Lesser flooding losses probably occur in most years. Nesting colonies on the Mary River are likely to suffer higher flooding mortalities than on many other river systems.