Effects of cross-sectional geometry, vegetation and ice on flow resistance and conveyance of natural rivers

The accurate estimation of local hydraulics, i.e. local flow velocities and water depths, is necessary for the restoration and protection of biodiversity. The aim of the thesis was to develop methods and models for designing and evaluating the hydraulic aspects of restoration, rehabilitation and environmental flood management in running waters. Methods for the estimation of flow resistance in natural complex rivers and channels that have composite flow resistance and/or a compound channel shape were tested, and an unsteady 1D flow model for partially vegetated channels with complex geometry was developed. These methods were used to quantify different factors causing flow resistance, e.g. cross-sectional geometry, vegetation, ice cover and momentum transfer, in lowland rivers of different shapes and sizes. The relationship between the flow resistance and the cross-sectional geometry was analysed. Traditional methods used to estimate composite friction factors were found to be accurate in simple concave channels with simple hydraulic properties, but an adjustment of the methods would be necessary for reaches with significant head losses due to lateral momentum transfer. It was seen that the effect of the momentum exchange process between the main channel and the floodplain or streambank vegetation was significant. A procedure for applying the success criteria in a post-project evaluation of local hydraulics was developed, based on the hypothesis of flow resistance and cross-sectional geometry determining local hydraulic conditions in boreal streams. Based on the results from the proposed flow model, the restoration of flood retention areas and local hydraulics is a vital component of the restoration of catchment-scale hydrology, but not sufficient by itself to restore flood peaks to their earlier state, because the changes in land use have often been drastic.reviewe

Practical aspects of integrated 1D2D flood modelling of urban floodplains using LiDAR topography data

Flood risk, a major risk facing mankind today, is projected to aggravate in view of the future predictions pertaining to the assessment of climate change scenarios. Traditionally, flood risk assessment exercises of urban floodplains have been carried out using 1D model as well as 1D model with storage cells. In view of the recent availability of high quality Light Detection and Ranging (LiDAR) topography data, availability of higher computing capacities, developments in the numerical computing techniques and the merits of an integrated 1D2D computing modelling method, integrated 1D2D modelling has gained a momentum for strategic flood risk management (SFRM) and detailed urban flood risk analysis. The research discussed in this thesis evaluates this modelling method using high quality LiDAR data in light of the results from the traditionally used 1D model with storage cells modelling method. The research study was carried out using laboratory experimental observation data, hypothetical urban floodplain data and data for a section of the River Clyde and adjoining urban floodplain in Glasgow, a major city in Scotland, UK. It concludes that, while integrated 1D2D models are of much benefit for a detailed flood risk analysis, specific attention needs to be paid towards the lateral extents of 1D model and the source of the river bank elevations while integrating it with a 2D model, particularly so when such a study is carried out for urban floodplains; and that the high quality LiDAR data significantly facilitates Strategic Flood Risk Modelling (SRFM) of urban floodplains

Numerical study of solitary wave propagating through vegetation

Ph.DDOCTOR OF PHILOSOPH