River Alyn, Flintshire, Wales- Flood Risk Assessment

According to physicians, fluid flow can be unstable or steady, viscous or non-viscous, compressible or incompressible, and rotary or rotating, to name a few characteristics. It is clear that some of these behaviors reflect the entire fluid properties, whereas others focus on how liquid travels. It is important to highlight in the literature by (Frick-Trzebitzky, Baghel, and Bruns,2017.p 5) that turbulent liquid flow can be difficult. The report demonstrates that how turbulence works is dependent on a specific system, hence no proper definition has been provided. Streamline flow in liquid occurs once the fluid flows in a parallel direction with limited or no disruption between layers. Research has shown that at low velocities the fluid flows without mixing laterally where adjacent layers slide past one another. In this context, there are limited close current perpendiculars to the flow direction (Peterson et al 2013.p. 13).

Laminar flow presents the motions of liquid particles in an orderly manner where these molecules are close to the reliable service, and they move in a straight-line co-current to that surface. Available literature show that streamlines flow is often characterized by low momentum convection and high momentum diffusion (Heyhat et al, 2013.p.21). Physicians have proved that whenever a fluid is flowing in a closed system or between flat plates turbulent or laminar flow may occur depending on the velocity and viscosity available. It is evident that laminar flows mostly happen at low speeds. On the other hand, contrast to laminar flow is turbulent flow that involves fluid undergoing irregular mixing or fluctuations (Jongma et al 2014.p.12). According to Borga et al, (2014.p.17) turbulent flow has diverse speed of liquid at particular point and gradually changes in direction and magnitude this is evident in river Alyn. Through activities such as surfing, smoke, from chimney and fast flowing rivers presents turbulent flows( Houssais et al 2016.p 43). According to physicians turbulent is because of massive kinetic energy, in particular, a section of liquid flow that overwhelms the damping effect of fluid viscosity. Due to this factor, turbulence is visible in liquids with low viscosity where unsteady vortices emerge in various sizes that interact with one another. In the literature developed by Plank and Prestegaard, ( 2016.p. 22) flow types are critical to appreciate the river response of the river bends and flood events. This report stated that a variety of natural rivers consists of subcritical and are turbulent in nature. The author explained that in the flooding event, the flow regime turns into turbulent or making eddies in specific parts with differences in flow velocities and a mix of those disparities causes’ turbulent reactions.

The report illustrate eddy formation as an important turbulence mechanism that aids in water transport and it is a significant tool in changing the flow resistance that is majorly associated with bend roughness. Another research concluded that flow resistance is associated with flow velocity in that it is capable of affecting flood events and pick discharge. In rivers with low velocities, less than 20km /h consists of a higher energy loss associated to bed form resistance (Ling et al. 2014.p 13). Researchers utilize various forms of alluvial channel resistance to illustrate flow resistance. The most used formula that relates to open channel flow speed is the Manning, Chezy, and Darcy-Weisbach formulae. The Manning model utilizes estimated data collected by an environmental department. The formulae’s value of n is equal to 0.035 and it is a distinctive of a natural system consisting of vegetation. However, in a well-managed system the value n can shift to 0.025. On particular areas, with mostly overgrown ecologies, the value can be as high as 0.050. Therefore selecting a suitable value to use these formulae is essential to producing collect outcomes.

Flood Estimation

Flood computation is mostly completed using convolution and computation of structure unit’s hydrograph. According to Alfier et al,(2014.p. 16) a unit hydrograph can be defined as conceptual system that is used to calculate the total runoff hydrograph at a particular point where liquid flow originates from a catchment area well known as outlet. The author illustrates runoff to contain direct runoff and the base flow. He defines base flow as a manageable dry weather flow that exists in rivers irrespective of service runoff due to rainfall. The base flow consists of two components the snowmelt and the contributed groundwater to river ecology. The report revealed that large rivers consisting snowbound regions are capable of receiving high levels of snowmelt in their upper areas, but in lower regions of the river, the base flow is mainly contributed by service runoff water. Researchers illustrate a unit hydrograph as a unique theory in that its time, base, and peak ordinate are always the same regardless of other meteorological and physiographical factors. The concept portrays a uniformly spread rainfall excess over time and space in a river basin.

The hydrograph theory present a unit depth assumed to be one cm. in another report done by Boers et al, (2014.p. 17) a unit hydrograph for a river basin is characterized by unit duration. A unit depth of excessive rainfall systematically generates over the entire river at this time. The author states that the theory is limited to some aspect such as it is challenging to have a uniform excess rainfall spread in a particular time and space over the entire river basin and unit duration and thus this concept maybe invalid for large rivers. Two the concept is limited to and can be applied to standardly shaped river basins. Another limitation is that it is a linear concept that uses homogeneity and superposition to hold goods. Blöschl et al, (2017.p.26) stated that isolated storms provide single picked hydrograph unit at the outlet and thus derivation of the unit hydrograph can be calculated by analyzing the storm’s hydrograph as well as analyzing the storms rainfall. According to Madsen et al, (2015.p.32) a unit, hydrograph conducted for ungauged rivers is calculated by observing the unit hydrograph parameters with a river’s physiographic a process known as synthetic unit hydrograph. The process is conducted in two steps. One the location of a station on a toposheet is analyzed and relevant information is derived. Two there is a massive analysis of physiographic data. Many small rivers ungauged often builds problems since ungauged flood’s estimates are massively more challenging on smaller rivers than bigger ones due to availabilities of surface runoff characteristic. The author states that flood estimation challenges are available due to lack of flood peak data.

Practically, many hydraulic systems are utilized to control surface runoff and they are set in regions where flood estimation methods are needed. In such a context, two primary techniques are used. These are statistical based and deterministic techniques. According to FSR floods, report unit hydrograph method and rational techniques are used to estimate floods structure for UK Rivers. Later the findings was overtaken by FEH (Flood Estimation Handbook) which derived an equation objected to improve the characteristic of floods response to small rivers. In the current world, flood estimate are derived using a rational method or by a formulae based on river’s behaviors such as those made by FEH and FSR. Sewell et al,(2014.p.22) argued that these two methods uses specific rivers descriptors to evaluate an index flood magnitude such as annual medium and maximum flood estimation that can be multiplied later by a suitable locational flood frequency factor to result to flood estimate. Subsequently, these values are compared to the flood frequency for their respective rivers to make a return time of two, 5,10,25,50 or a 100 years. The author argued that frequency of flooding is illustrated by the frequency of the yearly maximum expulsion of a catchment that occurs at a particular time. Despite the limitation of the theories, they are still used together with statistical techniques of flood frequency where estimation of entire flood hydrograph is needed (Foulds, Griffiths, Macklin and Brewer, 2014.p. 26). The technique can be used to estimate wholesome flow from a particular rainfall event whether designed storm or observed event. The designer of the model presented the efficiency of the UH as it provided graphs that were uniform in time and space over the total river basin. Beside the challenges faced in the result by overestimating, the flood risk is due to risk multiplication that is not reliable. According to Kvočka, Falconer and Bray, (2015.p. 17) the possibility for overestimating emerges from little attention presented in the use of flood frequency in ungauged rivers.

Flood Management

Rivers particularly big ones are capable of causing disasters when they flood. They are not limited to causing economic damage, destroying livelihood, or killing people. Geaves, and Penning-Rowsell, (2015.p.31) stated that it is not surprising for people to try to stop river flooding using a variety of resources and techniques despite unpredictable and powerful factors of rivers. To stop rivers from flooding is not an easy thing but many activities can be done to mitigate or manage risks associated with flooding. The author stated that flood management structures, in general, should be used to control the risks by setting up artificial systems that combine with science and innovation to hinder rivers from flooding. Paul, Rahman and Haque, (2016. P. 34) argues that the constructed artificial uses the local people know and natural resources of the catchment to minimize risks associated with flooding. The author adds that human effect can cause flooding from building floodplains, poor flood defenses and using ineffective river management systems.

Due to the construction of flood-prone land and settlement evaluated that losses caused by floods in urban areas are significant in mitigating flood disaster (Jeffery, 2016.p. 43) Therefore, flood risk management is the procedure of controlling an existing flood situation objected to reducing the negative results of the flood. In the literature done by Ji, (2017.p. 33), it is evident that setting up flood management structures is a compromise between preservation of natural resources and safety. Strategies employed to mitigate floods has widely become accepted due to the utilization of principles, models, and extensive flood risk evaluation. The available literature reveals that management strategies are derived not only to prevent flooding but also to permit specified regions to flood in this context ‘flood detention’. Cinderby and Forrester, (2016.p. 27) stated that a flood detention location serves the fundamental objective of controlling water storage during flooding event to reduce flood risks at the lower areas of the river. It is evident that disparities between river basins have a significant effect on the frequency and magnitude of the flood (Fielding, 2017.p.34). Rural areas are considered the most sensitive locations to flood particularly during winters. On the other hand, urban areas are also at higher risk of floods due to the intense storms facilitated by dry nature of the areas. Utilizing river basin information acquired using physical properties and flow indicators enables people to develop efficient flood management structures

Reference list

Alfieri, L., Burek, P., Feyen, L. and Forzieri, G., 2015. Global warming increases the frequency of river floods in Europe. Hydrology and Earth System Sciences, 19(5), pp.2247-2260.

Aziz, K., Rahman, A., Shamseldin, A. and Shoaib, M., 2013. Regional flood estimation in Australia: application of gene expression programming and artificial neural network techniques. In Adapting to Change: the Multiple Roles of Modelling: Proceedings of the 20th International Congress on Modelling and Simulation (MODSIM2013), 1-6 December 2013, Adelaide, South Australia (pp. 2283-2289).

Benson, D., Lorenzoni, I. and Cook, H., 2016. Evaluating social learning in England flood risk management: an ‘individual-community interaction’perspective. Environmental Science & Policy, 55, pp.326-334.

Blöschl, G., Hall, J., Parajka, J., Perdigão, R.A., Merz, B., Arheimer, B., Aronica, G.T., Bilibashi, A., Bonacci, O., Borga, M. and Čanjevac, I., 2017. Changing climate shifts timing of European floods. Science, 357(6351), pp.588-590.

Boers, N., Bookhagen, B., Barbosa, H.M., Marwan, N., Kurths, J. and Marengo, J.A., 2014. Prediction of extreme floods in the eastern Central Andes based on a complex networks approach. Nature communications, 5, p.ncomms6199.

Borga, M., Stoffel, M., Marchi, L., Marra, F. and Jakob, M., 2014. Hydrogeomorphic response to extreme rainfall in headwater systems: flash floods and debris flows. Journal of Hydrology, 518, pp.194-205.

Cinderby, S. and Forrester, J.M., 2016. Co-designing Possible Flooding Solutions: Participatory Mapping Methods to Identify Flood Management Options from a UK Borders Case Study. Journal for Geographic Information Science, pp.149-156.

Fielding, J.L., 2017. Flood risk and inequalities between ethnic groups in the floodplains of England and Wales. Disasters.

Foulds, S.A. and Macklin, M.G., 2016. A hydrogeomorphic assessment of twenty‐first century floods in the UK. Earth Surface Processes and Landforms, 41(2), pp.256-270.

Foulds, S.A., Griffiths, H.M., Macklin, M.G. and Brewer, P.A., 2014. Geomorphological records of extreme floods and their relationship to decadal-scale climate change. Geomorphology, 216, pp.193-207.

Frick-Trzebitzky, F., Baghel, R. and Bruns, A., 2017. Institutional bricolage and the production of vulnerability to floods in an urbanising delta in Accra. International Journal of Disaster Risk Reduction, 26, pp.57-68.

Geaves, L.H. and Penning-Rowsell, E.C., 2015. ‘Contractual’and ‘cooperative’civic engagement: The emergence and roles of ‘flood action groups’ in England and Wales. Ambio, 44(5), pp.440-451.

Gimbert, F., Tsai, V.C. and Lamb, M.P., 2014. A physical model for seismic noise generation by turbulent flow in rivers. Journal of Geophysical Research: Earth Surface, 119(10), pp.2209-2238.

Heyhat, M.M., Kowsary, F., Rashidi, A.M., Momenpour, M.H. and Amrollahi, A., 2013. Experimental investigation of laminar convective heat transfer and pressure drop of water-based Al 2 O 3 nanofluids in fully developed flow regime. Experimental Thermal and Fluid Science, 44, pp.483-489.

Houssais, M., Ortiz, C.P., Durian, D.J. and Jerolmack, D.J., 2016. Rheology of sediment transported by a laminar flow. Physical Review E, 94(6), p.062609.

Janes, V.J., Grabowski, R.C., Mant, J., Allen, D., Morse, J.L. and Haynes, H., 2017. The Impacts of Natural Flood Management Approaches on In‐Channel Sediment Quality. River Research and Applications, 33(1), pp.89-101.

Jeffery, C., 2016. Ephemeral Coast, S. Wales. Lulu. com.

Ji, Z.G., 2017. Hydrodynamics and water quality: modeling rivers, lakes, and estuaries. John Wiley & Sons. Wu, H., Adler, R.F., Tian, Y., Huffman, G.J., Li, H. and Wang, J., 2014. Real‐time global flood estimation using satellite‐based precipitation and a coupled land surface and routing model. Water Resources Research, 50(3), pp.2693-2717.

Jongman, B., Hochrainer-Stigler, S., Feyen, L., Aerts, J.C., Mechler, R., Botzen, W.W., Bouwer, L.M., Pflug, G., Rojas, R. and Ward, P.J., 2014. Increasing stress on disaster-risk finance due to large floods. Nature Climate Change, 4(4), pp.264-268.

Jongman, B., Winsemius, H.C., Aerts, J.C., de Perez, E.C., van Aalst, M.K., Kron, W. and Ward, P.J., 2015. Declining vulnerability to river floods and the global benefits of adaptation. Proceedings of the National Academy of Sciences, 112(18), pp.E2271-E2280.

Kvočka, D., Falconer, R.A. and Bray, M., 2015. Appropriate model use for predicting elevations and inundation extent for extreme flood events. Natural Hazards, 79(3), pp.1791-1808.

Ling, F.L.N., Pokhrel, P., Cohen, W.J., Robinson, K.A. and Blundy, S., 2015. Testing of Monte Carlo and design event models for flood estimation. In 36th Hydrology and Water Resources Symposium: The art and science of water (p. 104). Engineers Australia.

Madsen, H., Lawrence, D., Lang, M., Martinkova, M. and Kjeldsen, T.R., 2014. Review of trend analysis and climate change projections of extreme precipitation and floods in Europe. Journal of Hydrology, 519, pp.3634-3650.

Marsh, T. and Sanderson, F., 2014. The 2000/01 floods: a hydrological appraisal.

Parry, S., Marsh, T. and Kendon, M., 2013. 2012: from drought to floods in England and Wales. Weather, 68(10), pp.268-274.

Paul, H., Rahman, A. and Haque, M., 2016. Application of ARR FLIKE for at-site flood frequency analysis: A case study in New South Wales, Australia. In 37th Hydrology & Water Resources Symposium 2016: Water, Infrastructure and the Environment (p. 367). Engineers Australia.

Peterson, T.C., Heim Jr, R.R., Hirsch, R., Kaiser, D.P., Brooks, H., Diffenbaugh, N.S., Dole, R.M., Giovannettone, J.P., Guirguis, K., Karl, T.R. and Katz, R.W., 2013. Monitoring and understanding changes in heat waves, cold waves, floods, and droughts in the United States: state of knowledge. Bulletin of the American Meteorological Society, 94(6), pp.821-834.

Plank, C. and Prestegaard, K.L., 2016, February. Large Floods in Narrow Valleys and Wide Floodplains: The Hydro-Climatology and Geomorphology of Flooding in Atlantic Slope Watersheds. In AGU Fall Meeting Abstracts.

Rosner, A., Vogel, R.M. and Kirshen, P.H., 2014. A risk‐based approach to flood management decisions in a nonstationary world. Water Resources Research, 50(3), pp.1928-1942.

Sewell, T., Stephens, R.E., Dominey-Howes, D., Bruce, E. and Perkins-Kirkpatrick, S., 2016. Disaster declarations associated with bushfires, floods and storms in New South Wales, Australia between 2004 and 2014. Scientific reports, 6.

Yang, Y., Liu, X. and Zhang, M., 2015. Instability of Laminar Flow in Wide Shallow Meander Channel. Journal of Coastal Research, 73(sp1), pp.542-547.