Floodplain

The article presents the results of soil and archaeological study of the pedo-sedimentation sequence formed in the floodplain of the Derkul River (West Kazakhstan). The aim of the study was to reconstruct the stages of the alluvial sedimentogenesis alternating with relatively prolonged spans of soil formation, corresponding to the periods of floodplain agricultural development. It was established that floodplain sediment layer started to form as a result of stream sedimentation in the early Holocene; then this stage was followed by the relatively long-term soil formation period (5.6–3.8 cal. yr BC) resulting in a humus quasi-gleyic soil in the low floodplain (120–200 cm). The last period of soil formation (4.6–3.6 cal. yr BC) the floodplain was developed by man, which is displayed by the identified cultural horizon containing artifacts and having increased phosphorus content. At the end of the Subboreal period the next stage of alluvial sedimentation, started by the changed river hydrology regime, was found to be chronologically separated from the stage of stationary development of the floodplain by settled humans.

The emergence of the study of fluvial dynamics of the alluvial monsoon rivers especially in India is being enriched through the application of remote sensing and GIS techniques. To study fluvial dynamics over time, channel avulsion no doubt is one of the most considerable phenomena. The study section (*75 km) in between the two confluences of the Bhagirathi River i.e., Ajay (Katwa) and Jalangi River (Nabadwip) confluence in Lower Ganga Plain of West Bengal is highly oscillatory in nature. Several satellite images and toposheets of different time periods (1955, 1973, 1990 and 2011) have been used in order to analyse the avulsive nature in this section of the river. These fluvial features (cut offs, ox-bow lakes, point bars etc.) form as a result of channel avulsion and have been identified with the help of Landsat satellite images. The decadal differences in sinuosity ratio in different parts of the studied section, channel migration rate and avulsion model explain the dynamic nature and crucial portions of high bank erosion rate of the channel in the mentioned time period. For both the reaches (R1 and R2), meander loop cut offs are dominant rather than lateral avulsion in the context of aggregate channel migration that also reflects the instability and erosional vulnerability at different meander bends.

Valley floor geomorphology, sedimentology and radiocarbon dating have been used to reconstruct variations in flooding during the Holocene at six sites within the upper Severn, Teifi and Dee catchments in Wales, UK. High-magnitude palaeoflood deposits, for which ages were estimated, were identified at three floodbasin sites in the upper Severn and Teifi catchments. At the remaining sites fluvial discontinuities, indicative of episodes of increased flooding, were identified. Data from these six sites, and six additional sites studied previously, indicate that seven probably centennial length episodes of major flooding have occurred in Wales since c. 7000 cal BP. These flooding episodes occur at similar times to peaks in flood frequency within Great Britain as a whole.

In floodplains, anthropogenic features such as levees or road scarps, control and influence flows. An up-to-date and accurate digital data about these features are deeply needed for irrigation and flood mitigation purposes. Nowadays, LiDAR Digital Terrain Models (DTMs) covering large areas are available for public authorities, and there is a widespread interest in the application of such models for the automatic or semiautomatic recognition of features. The automatic recognition of levees and road scarps from these models can offer a quick and accurate method to improve topographic databases for large-scale applications. In mountainous contexts, geomorphometric indicators derived from DTMs have been proven to be reliable for feasible applications, and the use of statistical operators as thresholds showed a high reliability to identify features. The goal of this research is to test if similar approaches can be feasible also in floodplains. Three different parameters are tested at different scales on LiDAR DTM. The boxplot is applied to identify an objective threshold for feature extraction, and a filtering procedure is proposed to improve the quality of the extractions. This analysis, in line with other works for different environments, underlined (1) how statistical parameters can offer an objective threshold to identify features with varying shapes, size and height; (2) that the effectiveness of topographic parameters to identify anthropogenic features is related to the dimension of the investigated areas. The analysis also showed that the shape of the investigated area has not much influence on the quality of the results. While the effectiveness of residual topography had already been proven, the proposed study underlined how the use of entropy can anyway provide good extractions, with an overall quality comparable to the one offered by residual topography, and with the only limitation that the extracted features are slightly wider than the investigated one. Copyright © 2013 John Wiley & Sons, Ltd.

Extremely high river discharges in 1993 and 1995 along the Dutch rivers Rhine and Meuse have increased the public awareness of possible safety threats. As a result the ‘Space for Rivers’ program was implemented, aiming at restoring physical space for the rivers in combination with ecological rehabilitation. However, the development of species-rich vegetation types in these floodplain areas is lagging behind restoration targets and biogeochemical constraints may play a vital role in this.Biogeochemical, hydrological and vegetation data were collected in 111 plots in both rehabilitated and original floodplains in regulated and more pristine river systems in The Netherlands and Poland. Soil nutrient and soil pore water data were summarized by factor analysis and the subsequent principal components were compared to vegetation and hydrological data by correlation analysis. The correlation analyses between vegetation parameters including nutrient stoichiometry and the biogeochemical soil variables resulted in a remarkable difference between pristine and impacted river systems. The results suggest a clear N-limitation of plant growth in pristine floodplains, and apparent absence of limitation in regulated, impacted floodplains. In addition, results indicate that flooding events do not lead to one-way transport of sediment and nutrients from the river into the floodplains; rather they indicate that highly dynamic hydrological conditions prevent soils from accumulating organic matter and nutrients.This study shows that nutrient limitation in regulated floodplains shifted from distinctly N-limited plant growth to no nutrient limitation at all, probably due to decades of high fertilizer and manure application and nutrient input by the rivers during flooding. The consequence of our findings for rehabilitation activities is that it might be necessary to restore nitrogen limitation in floodplain systems in order to create opportunities for a species-rich floodplain vegetation, through nutrient removal by hay-making. Copyright © 2006 John Wiley & Sons, Ltd.

After a long period in which fuel loads were sparse, fire recently has occurred with high frequency in the ungrazed riparian zone of the Upper San Pedro River in southern Arizona’s Chihuahuan Desert. We studied four accidental fires that occurred during 1994–2003 (two in different years at the same site). Woody vegetation was contrasted between three burned sites and matched spatial controls, and before and after the most recent fire. Herbaceous vegetation was sampled in multiple years producing a chronosequence of time since fire (from 4 months to 8 years). Riparian fire was associated with reductions in woody plant species diversity and canopy cover. In contrast, fire caused a short-term (2 year) pulse of herbaceous plant diversity, driven by annual species, and persistent increase in herbaceous cover. Path analysis indicated that the increase in herbaceous cover was mediated in part by the reduction in tree canopy cover. Ordination (nonmetric multidimensional scaling) and regression analysis also indicated that canopy cover and/or fire played a role in structuring the herbaceous community, although its effects were secondary to that of hydrologic factors (stream flow rate, seasonal flood size). By converting riparian forests to grasslands and savannahs, fire may be shifting structure of the Upper San Pedro floodplain vegetation closer toward conditions present during past centuries when fire was frequent in the upland desert grasslands and embedded riparian corridor.

The acquisition of high quality, well dated local site records is essential for progressing regional environmental reconstructions. As part of a wider study designed to examine intra- and extra- site ecosystem responses to environmental change, this paper presents new palaeoecological data from the floodplain of the River Torne in the Humberhead Levels, adjacent to the lowland raised mire of Hatfield Moors, a site with a long history of palaeoecological investigations. The potential of using floodplain records to reconstruct local variations in ecosystem response to environmental change is also considered. Coleoptera and pollen are used to reconstruct floodplain ecosystem dynamics, whilst chronologies are established using Bayesian age-depth modelling. Between 10200 cal BP and 2300 cal BP, the floodplain experienced multiple phases of ecological change. At 10200-9910 cal BP, a cut-off channel began to infill with peat, while the surrounding floodplain remained relatively dry with Pinus forest growing nearby. Between 9630-9500 cal BP and 7270-7020 cal BP, a depositional hiatus occurred in the sedimentary record. By the end of this period, the local woodland had diversified and expanded to mixed deciduous tree cover. A wet shift identified at 6870-6160 cal BP was shortly followed by a rise in Alnus and Tilia from 6410-6160 cal BP. At this time, widespread floodplain paludification had occurred in the Humberhead Levels, which was largely controlled by Relative Sea-Level (RSL) rise and the associated rise in regional water tables. Floodplain expansion also resulted in the widespread occurrence of Alnus dominated fen woodland. The local Torne floodplain experienced varying levels of wetness that influenced the decline and subsequent regeneration of the woodland from 5870-5640 cal BP. At this time, the Ulmus decline is identified in the pollen stratigraphic record. Floodplain hydrology appears to have been controlled by a combination of water table fluctuations and changes in channel pattern/flow, both of which can be linked to RSL variations recorded in the Humber Estuary. Floodplain alluviation, also linked to rising water tables, is dated to 4360-4160 cal BP. Anthropogenic woodland clearance further upstream may have further compounded this event. We emphasise the importance of obtaining well-considered, securely dated local palaeoecological reconstructions prior to examining regional patterns of change.

Background and Objectives: The floodplains are relatively flat lands in the vicinity of the rivers with the residential, industrial or agricultural usage. The sudden breakdown of large dams leads to the formation and propagation of devastating flood waves over the downstream. The flood propagation occurs over the floodplains due to the topographic variations and in-stream obstacles such as bridges. These waves are developed one and two dimensional over a small reach of the river and floodplains, respectively. In the hydrodynamic simulations, two-dimensional characteristics of the dam-break flow over the floodplains have been studied scarcely. Therefore, the combined effects of the floodplains obstacles, constriction and the bottom barriers are calculated over the dam-break flow characteristics.
Materials and Methods: In the present study, the moving particle semi-implicit (MPS) method was used to the numerical study of the dam-break flow characteristics over the floodplain. From advantages of this method are including the incompressibility, the particle-based and using of powerful models of gradients and Laplacian in velocity-pressure corrections without any complex smoothing functions. Hence, the effects of the reservoir initial water level, the shapes of the obstacles - lateral transitions as well as the bottom barriers on the hydraulic parameters were studied in 15 various cases. The floodplain obstacles are cylindrical, cubic, rhomboidal and asymmetric, and the bottom barriers are cubic. At first, the sensitivity analysis was carried out on three particles diameters including the 0.01, 0.015 and 0.20 m. Finally, the diameter of the particles equal to 0.015m was adopted as the water particles size in the model. The simulations carried out through more than 280000 spherical particles, with the second order spatial and temporal accuracy.
Results: The precision of the numerical results was calculated using the NRMSE normal error through the comparison with the previous experimental one. The results demonstrated that evacuation of the reservoir occurs in numerical solutions faster than the experimental. Therefore, the MPS model under and overestimates the values of the free-surface profile height and the flow propagation velocity, respectively. The impact of flow to the floodplain obstacles leads to the rising up and the formation of a three-dimensional flow at the obstacles place, the lateral constrictions and the bottom obstacles. Further, the shape of the obstacles represents a crucial factor in the free surface profile deformations, the horizontal component of the surface velocity, and the drag resistance forces applied to the flow.
Conclusion: Normal error values showed that the accuracy of the MPS method in the calculation of the free surface longitudinal profile deformations are variable between 88 and 91 percent.

River regulation has led to a decline in the condition of Australia’s dominant riverine tree species, Eucalyptus camaldulensis Dehnh., in the Murray-Darling Basin.  A quantitative method of assessing the condition of these important riparian forests is required for effective monitoring and management.  A range of stand structural, morphological and physiological variables was measured in stands of contrasting condition along the Murray River in southeastern Australia.  Percentage live basal area, plant area index and crown vigour were found to be reliable, objective indicators of stand condition.  Little difference was detected in the physiological performance of trees in terms of water potential and chlorophyll fluorescence among stands of good and poor condition.