Hydraulic Resistance of Vegetation in River Flow Applications

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732If vegetated regions become part of a river’s flow field, the hydraulic resistance of vegetation affects the overall conveyance. Several descriptions exist to describe this type of flow; among them are empirical relations and relations that are process-based. In the current work three expressions are considered that have equal input parameters, similar levels of complexity but different theoretical backgrounds. The performance of the three methods is evaluated by comparison with flow measurements (collected from literature), and limits are given for their practical use

Remediation of Contaminated Soils by Solvent Flushing

Solvent flushing is a potential technique for remediating a waste disposal/spill site contaminated with organic chemicals. This technique involves the injection of a solvent mixture (e.g., water plus alcohols) that enhances contaminant solubility, reduces the retardation factor, and increases the release rates of the contaminants. A simulation model is developed to predict contaminant elution curves during solvent flushing for the case of one‐dimensional, steady flow through a contaminated medium. Column experiments are conducted with a Eustis fine sand that is initially equilibrated with an aqueous naphthalene solution, and then eluted with different methanol‐water mixtures to remove the naphthalene. The model simulations, based on parameter values estimated from literature data, agree well with the measured elution profiles. Solvent flushing experiments, where the soil was initially equilibrated with a solution of naphthalene and anthracene, show that compounds with different retardation factors are separated at low cosolvent contents, while coelution of the compounds occurs at higher contents. In general, the smaller the retardation factor in water and the higher the cosolvent fraction, the faster the contaminant is recovered. The presence of nonequilibrium conditions, soil heterogeneity, and type of cosolvent will influence the time required to recover the contaminant.\u

Reorganization of water and waste water management in Romania:from local to regional water governance

Romania's drinking water and wastewater sector is currently going through a process of regionalization. This process involves a replacement of a local-focused governance structure by a regional-focused governance structure. The objective of this paper is to explore and explain this regionalization from a governance perspective. In two case studies, the situation before and after the regionalization are investigated. Analyses of the case studies show that the local-focused governance structure was highly incoherent. This resulted in a lack of financial resources needed to maintain and develop the water infrastructure. Romania's accession to the European Union affected several governance elements and evoked the regionalization. Real improvements are not visible yet as the time needed for actual services improvements is considerable and governance elements are still adjusting to each other. This means that there is still a need for ongoing support to arrive at a coherent governance structure

Analyzing natural bed‐level dynamics to mitigate the morphological impact of river interventions

Local river interventions, such as channel narrowing or side channels, are often nec-essary to maintain safety, ecology, or navigation. Such interventions have differenteffects on the river's bed morphology during periods of high- and low-dischargeevents. Mapping the bed-level variations for different discharge levels and under-standing these effects can provide new opportunities for the design of interventionsin multifunctional rivers. At any moment, the local bed level in a river is composed ofbed-level changes that occur at various spatial and temporal scales. These changesconsist of bed aggradation/degradation trends on a large scale, on an intermediatescale bed-level variations as a result of discharge fluctuations, and on small-scalemoving river bed forms like dunes. Using the river Waal in the Netherlands as a casestudy, we analyze the intermediate-term bed-level changes resulting from dischargefluctuations (dynamic component) and propose adaptations to the design of flood-plain interventions such that possible negative impact on the local bed-level changesis minimized. Time series of bed levels along two 10 km stretches of the case studyare considered for a period of 16 years (2005–2020). Using a wavelet transform, weisolate bed-level variations resulting from discharge events. These bed-level varia-tions are presented based on the magnitude of the discharge event and are compiledin an interactive atlas of river morphodynamics, allowing us to mitigate the impact ofinterventions. This will help river managers in the design of interventions and lead toimproved management, operation, and maintenance of multifunctional rivers

Revealing 35 years of landcover dynamics in floodplains of trained lowland rivers using satellite data

Lacking substantial erosive and sedimentation forces, regulated rivers allow their floodplains to become overgrown with forest, increasing the flood risk of the hinterland. In the Netherlands, floodplains have therefore been subjected to interventions, like clear cutting, lowering and creation of side channels, and management, consisting of grazing and mowing. However, the comprehension of how those activities influence landcover dynamics is lacking. The aim of this study is therefore to investigate long‐term landcover dynamics of a regulated river system through the lens of remote sensing. What transitions between landcover classes can be observed? And how (if) do management and interventions impact succession and retrogression of landcover classes? The study area comprised the upstream part of the Dutch Rhine River, its three branches and five adjacent floodplains. Satellite data (LandSat 5 and 8), encompassing a 35‐year period (1984–2018), were used for studying landcover dynamics. Landcover classification was based on seven classes: water, built‐up area, bare substrate, grass, herbaceous vegetation, shrubs and forest. Retrogression was highest for the landcover classes obstructing water flow (shrubs, forest and herbaceous vegetation), succession was most frequent on bare substrate, and water and grass were the most stable landcover classes. The regulated nature of the system became apparent from the spatial and temporal cacophony of landcover dynamics which differ from those of natural meandering rivers. This study showed that satellite data are useful for analyzing the impact of human activities within floodplains of regulated rivers and may assist in floodplain management aimed at combining water safety and nature policies

Analytical solution of the depth-averaged flow velocity in case of submerged rigid cylindrical vegetation

A new model for the depth-averaged velocity for flow in presence of submerged vegetation is developed. The model is based on a two-layer approach, where flow above and through the vegetation layer is described separately. Vegetation is treated as a homogeneous field of identical cylindrical stems, and the flow field is considered stationary and uniform. It is demonstrated that scaling considerations of the bulk flow field can be used to avoid complications associated with smaller scale flow processes and that still the behavior of depth-averaged flow over vegetation is described accurately. The derived scaling expression of the average flow field is simple in form, it follows fundamental laws of fluid flow, and it shows very good agreement with laboratory flume experiments. The new model can be used for quick evaluation of a river’s hydraulic response in cases where vegetated floodplains are inundated