The Phongolo River floodplain in KwaZulu/Natal is a river-associated wetland which was subject to regular cycles of flooding in the past. The floods were associated with seasonal summer rainfall. Through the wet and dry cycles on the floodplain there was an alternation between the aquatic and terrestrial biomes. Many of the fishes on the floodplain are dependent on this cycle for their survival. The construction of the Pongolapoort Dam in 1969 has resulted in alterations to the timing, magnitudes and duration of the natural flooding events of the Phongolo River. This alteration has affected the fisheries. It is now necessary to simulate natural floods by artificial water releases from the dam. There are several demands on the water supply, so it has not always been possible to adhere to the natural flood regime. This necessitated the need for an integrated management programme to ensure the sustainability of the natural resources. A practical ecological model of the fishery was developed to determine an optimum flood release scenario for the floodplain. The relative abundances, distribution and species richness of the fishes were determined at various lakes and rivers on the floodplain. A community classification of the fishes was determined using TWINSPAN ordination. The potential yield of the fish at each site was calculated. Flood releases of varying magnitudes were simulated using Geographic Information Systems (GIS). This information was combined in a model which can be used by resource managers to estimate the percentage species compositions of fishes at each of the lakes, and to compare the actual harvest to the potential calculated sustainable yields of fishes for various flood release regimes. Subsistence agriculture and other beneficial ecological information can be incorporated into the model to determine the effect of different flood release options for the Phongolo floodplain.

Wetlands are dynamic ecosystems and important sources of natural resources that provide a large array of ecosystem services. Unfortunately, most wetlands are threatened by human and natural stressors, such as damming, irrigation, water abstraction, climate change and variability that compromise the sustainability of the whole system. The Inner Niger Delta (IND), Mali, West Africa, is one of the biggest floodplains in the world, has a vast natural resource that attracts many people to live in and around the delta. The IND is considered a hub of human activities that include agriculture, fishing, transport, and tourism and plays an important role in promoting sustainable development for food security, water management, and the environment. As for most wetlands in the world, the very existence of the IND is at stake with the ever-increasing number of dams and irrigation schemes that are built to feed the growing population in the region. Given the fragility of the system and the multiplicity of water uses in the IND, the current knowledge of the flood dynamics and its relation to ecosystem services and the productivity of economic activity is insufficient. There is no operational hydrodynamic model of the IND, and the Malian authorities rely on simplified models and empirical relations for water resources management in the area. This thesis contributes to a better water resources management of the IND by a) developing the first 2D hydrodynamic model based on a triangular adaptative mesh of the IND that performs well despite the poor quality of available topographic/bathymetric data b) developing an innovative way of accounting for the strong hysteresis phenomenon in the IND in the hydrodynamic modeling that allowed a better reproduction of the hydraulic connectivity between important lakes and the main river and c) developing the first non-stationary relationship between the water levels at a reference station and the flooded area in the IND. The first part of the thesis deals with the challenge of developing a hydrodynamic model using only two low-resolution satellite-derived Digital Elevation Models: the Shuttle Radar Topography Mission (SRTM), which has a 30m horizontal resolution, and the Multi-Error-Removed Improved-Terrain (MERIT). Given the low vertical accuracy of global DEMs, another DEM was derived using the waterline method, by combining water extent map from satellite images and local water level information. Channel depths were approximated using the hydraulic geometric relationship methods, while the friction coefficient was derived from the global land-use class classification (GLCC) data. The river network was extracted from the water extent map corresponding to the lowest water level. Six different hydrodynamic models were created by varying the DEM and downstream boundary conditions. Each of the models was calibrated for discharge and water levels. Bayesian Model Averaging (BMA) was finally used to combine the outputs of all six hydrodynamic models into one robust simulation. In the second part, the effect of hysteresis at the downstream boundary condition of the hydrodynamic model was examined. Existing hydrodynamic models of the IND use a static stage-discharge relationship as a downstream boundary condition during both the rise and recession of the flood, leading to potential inaccuracies in the simulation of the flood extent. This paper explores the improvement in the simulation of the flood and connectivity dynamics resulting from the use of a looped rating curve at the downstream boundary of a hydrodynamic model of the IND. The hysteresis effect is integrated into the rating curve using two methods, one based on dimensionless discharges and levels (DLRC) and the other based on the modified Jones formula (MJRC). Results show that the hysteresis effect is better represented using DLRC and that simulations using any of the modified rating curves improves the accuracy of floodplain extent simulations in the areas close to the downstream station, as well as the timing of the connectivity of the river system to one important lake in the IND. The improvement in water level simulation decreases steadily with distance from the downstream boundary of the modeled area. The third part of the thesis deals with the development of an improved relation between inundation extent and water levels in the IND. Accurate knowledge of the flooded extent considered crucial for the proper management of natural resources in the IND. Several authors have developed empirical relationships between water levels at key stations in the IND and the flooded extent in an attempt to provide simple tools to link hydraulic parameters to the performance socio-economic activities in the IND. However, simulations from a hydrodynamic model of the IND showed that the relationship between water levels and the inundation extents varies greatly from year to year, and cannot be adequately captured by static formulas. First, it is demonstrated in this paper that if the maximum water level area is known in advance, accurate relationships between water levels and inundation extents can be derived. In the second part of the paper, stepwise regression is used to develop a function that can forecast maximum water levels at Akka using observed streamflow and precipitation upstream of the Delta. The combination of the two results allows a realtime estimation of the inundated area in the IND using observed water levels, precipitation, and streamflow.

No description available.

The cycling of phosphorus (P) through floodplain environments is critical to ecosystem productivity and has significant implications on both water quality and soil fertility. P export from soils in response to saturation has been well documented, but the relative vulnerability of specific P pools to mobilization remains poorly constrained, as do the mechanisms mediating its release. The prediction of P availability in and export from mountainous floodplain soils is of great importance as global climate change is projected to significantly alter precipitation regimes in alpine systems. This study combined a thorough characterization of P distribution across a hillslope to floodplain transect with a high resolution analysis of P response to saturation, providing insight into both P cycling and flood-induced mobilization in the East River watershed in Gothic, Colorado. P-XANES, 31P NMR, and sequential extractions revealed that P concentrations were greatest in the floodplain and dominated by inorganic P (Pi) bound to primary minerals, while hillslope P was lower and characterized by more bioavailable and organic (Po) pools. Time series analysis of P response to extended water saturation confirmed our hypothesis that P mobilization would occur in two phases, first driven by lysis of microbial cells upon initial rewetting, and later driven by the reductive dissolution of Fe oxides with extended saturation. These findings indicated that (i) the interaction of weathering and hydrology dictate P speciation across the transect; (ii) hillslope P may be concentrated in microbial pools while floodplain P is primarily bound by minerals; (iii) bioavailable P pools may be dominated by Po; and (iv) Po is more vulnerable to mobilization during initial rewetting of dried soils while Pi responds more to changes in redox potential during extended saturation. Results from this study underscore the significance of hydrology in determining P speciation and mobilization, indicating that long-term changes in precipitation may influence P bioavailability and export from alpine watersheds. Understanding the mechanisms by which P is mobilized is therefore of critical importance to better predict soil P response to saturation in a changing climate.

This work was focused on geochemical methods and analyses which were used for lithologic and facial description of floodplain sedimentary records and also for determination of depth dependence of Pb concentration and evaluation of possible mobility of Pb in six profiles, which were taken across the floodplain in two locations in the southern part of Morava River in study area called Strážnické Pomoraví. The aim was to confirm the stability of concentration of Pb in upper parts of all six profiles. Performing these analyses, a possible migration of Pb in lower parts of some profiles has unexpectedly been revealed. For better facial description of the profiles in floodplain fines, proxy methods such as cation exchange capacity (CEC), elementary analysis using energy dispersive X-ray fluorescence spectrometry (EDXRF) and also determination of content of magnetic particles using magnetic susceptibility in depth profiles were used. The results of these proxy methods were confirmed by conventionally used geochemical methods - BCR sequential extraction, elementary analysis with determination of Pb isotope ratios using ICP MS, and granulometric analysis.

Runion is a protohistoric Native American village located on the floodplain of the Nolichucky River in western Washington County. Previous archaeological excavations and radiocarbon dates suggest that the village was occupied during the mid-16th to mid-17th century. The Nolichucky River, in contrast, has been flowing through the area for millennia. Geophysical surveys are used to image the subsurface non-invasively, without disturbing protected land and/or organisms. Preliminary geophysical data collected at Runion include ground penetrating radar (GPR), electromagnetic induction (EMI), and magnetometry. These data show a linear feature surrounding the protohistoric village. Given its placement around the margins of the village, the feature could be interpreted as a fortification ditch, which is often paired with a palisade wall to defend a village from attack. The feature is also consistent with typical meandering floodplain stratigraphy, where sections of channel are often abandoned to form oxbow lakes. Over time these abandoned channels fill in and are called paleochannels. Each geophysical method measures the properties and characteristics of the linear feature, a presumed paleochannel. GPR sends electromagnetic radar waves into the ground, which reflect off different subsurface layers and are recorded as radargrams. Magnetometry measures subtle changes in earth magnetism, including the magnetization of rocks, soils, and/or ferrous objects. EMI systems transmit low frequency electromagnetic waves to measure both electrical conductivity (EC) and magnetic susceptibility (MS). Each of these instruments are used to collect data in transects and then processed to produce profiles, maps and, in the case of GPR, three-dimensional datasets of the subsurface. It is anticipated that GPR will reveal details about the stratigraphy of the linear feature. Magnetic, EC, and MS measurements will further help to interpret the GPR data by distinguishing between different types of sediments. These data may show if the feature is a paleochannel or a ditch excavated into older stratigraphic layers by village inhabitants for fortification. Ultimately, the feature will be tested with soil cores to study the sediments directly. At this preliminary stage the feature is interpreted to be a paleochannel. The stratigraphic layers revealed by GPR show a broad depression with stratigraphic layers characteristic of a paleochannel. In addition, magnetic readings are anomalously low on the eastern margin (closer to the modern river channel) and high on the western margin. This could indicate paired point bar sands and paleochannel fill, respectively. This interpretation is still tentative, however, because we have not yet integrated the EMI data, extracted soil cores, or dated the feature. Radiocarbon dates might help determine the relative age of the feature if organic carbon is present. In conclusion, preliminary data currently suggests that the structure is geological rather than archaeological. In the coming months we will collect more GPR data with different frequency GPR antennas, integrate the EMI data, and test the findings by extracting soil cores and reconstructing the stratigraphy.

<p>Disturbance regimes like freezing and thawing (FT) can have potentially significant impacts on nutrient release from soil and are predicted to increase with climate change. This is particularly important in biogeochemical hotspots like floodplains that can both remove and release nutrients to surface waters during flooding. Connection between the river and floodplain can improve water quality by reducing nutrient loads through microbial processes and sedimentation. However, conditions during flooding can also lead to phosphorus (P) release from pools that are not normally bioavailable. Disturbance events like FT can also lead to changes in bioavailable P due to microbial cell lysis. This study investigates differences in P chemistry and flux during flooding from intact soil cores that have undergone a FT cycle compared to soils that have not undergone freezing. Floodplain soils were collected from four sites along the Wabash and Tippecanoe Rivers in Indiana. We hypothesized that (i) the primary pools of P within the soil would change with freezing (ii) and flooding; (iii) frozen treatment cores would release more P during flood incubations than unfrozen control cores; and (iv) processes controlling P release during flood incubations would change after FT due to changes in the primary pools of P in the soil cores. </p> <p> </p> <p>On average, soil cores that underwent FT released greater amounts of P than unfrozen cores over the course of the 3-week experimental flood incubation. Phosphorus release in both unfrozen control and FT treatment cores during flooding was explained in part by soil extractable Al and Fe and redox status; however, P release was influenced by soil Ca-P in the FT cores to a greater extent than unfrozen cores. Phosphorus release in FT cores occurred faster than in control cores with overlying water concentrations peaking 2 weeks after onset of flooding, followed by lower concentrations at 3 weeks. Whereas control cores had some release and uptake early on but then released P throughout the 3-week incubation—supporting the hypothesis that drivers of P release were different after FT. Interactive effects of FT and flooding suggest that concentration gradients between soil pore water and overlying surface water could have enhanced dissolution of the Ca-P pool, highlighting the importance of floodwater chemistry to P dynamics following FT. This study provides an important link between observed winter floodplain P loss and potential drivers of release and retention, which is critical to informing floodplain restoration design and management through all seasons.</p>

A better understanding of transport and deposition of fine sediment in alluvial rivers, including their floodplains, is essential for improved understanding of sediment budgets and prediction of river morphological changes. Previous work in the Root River indicates that channel-floodplain sediment exchange exerts strong control on the sediment flux of this system. In addition, improvements in agricultural practices and increases in high and low flows during the past five decades have led us to believe that sediment sources in the Root River may be shifting from uplands to near-channel sources. This thesis estimated the total amount of fine sediment contributed to the channel from near-channel sources due to the processes of lateral channel adjustment (channel migration and channel widening) using a quantitative approach based on the use of multiple epochs of aerial photographs (1930s-2010s), lidar data available for the entire watershed from 2008, and other GIS analysis. The results obtained in this thesis serve as another line of evidence to constrain a sediment budget for the Root River watershed and to improve our understanding of the sediment dynamics within the watershed. In addition, we found that the Root River presents a marked division between its lateral channel adjustment trends before and after the 1970s. We also found that while increases in flows have affected lateral channel adjustment rates throughout the entire channel network, other factors like sediment supply and riparian vegetation may be playing an equally important role.

The aim of the thesis is hydraulic computation of shallow water flow in floodplains with using 2D numerical modelling. Processing river is Dyje in the south of Moravia in location Břeclav. For model creation is necessary to know the software, accumulate input data and prepare model input parameters. Output data are process to form of maps water depths and maps water flow velocities.

Student Number : 0413447J - MSc research report - School of Geography and Environmental Studies - Faculty of Science / This research analyses the vulnerability and adaptation of communities living along the River Kaduna floodplain at Shiroro Local Government in Niger State to flood occurrences. These communities are one of the most flood-prone areas in Niger State, with fertile alluvial deposits for agricultural production. The analysis of rainfall and flood flow into the Kaduna River System shows that there is an increasing flood frequency and flood magnitude along the River Kaduna for the past two decades because of slight increase in rainfall amount. Although there is a slight increase in rainfall amounts, the flooding of the Kaduna River could be regarded as normal. This is because there is no major change in rainfall amounts. Therefore, any slight increase in rainfall may cause flooding. The 1990s with slight increase in rainfall coincides with the period of abundant flood flow in the Kaduna River System and very significant runoff into the Kaduna reservoir. Floods have impacted negatively on the life of the people living on the floodplain resulting into food insecurity, poverty and vulnerability to malnutrition and other health problems among the communities in Shiroro Local Government Area. There are three vulnerable groups identified within the communities (the very poor, those residing on the floodplain and those that depend only on agriculture). These three groups identified lack accesses to good shelters and social amenities like electricity, good water, roads, health facilities and schools. Moreover, this research shows that the adaptive capacity of these communities is being severely compromised by factors such as poverty, poor infrastructure, weakening social networks and environmental degradation.