Flood Storage Reservoirs Research Articles

Leeds FAS2 FSR: environmental challenges for the design of an in-river control structure

As flood-risk authorities look to counter increasing peak river flows due to a changing climate, traditional linear flood defences are in many cases proving to be an unsustainable method of managing flood risk. Full containment of flows in the river channel will require ever-increasing defence heights, cutting off communities from their rivers and natural heritage. Upstream flood storage provides a potential alternative means of flood management, allowing the peak of the flood to attenuate and downstream river levels to be kept within a tolerable range. The Leeds Flood Alleviation Scheme Phase 2 uses a combined approach: linear defences are constructed in urban reaches and complemented by an online flood storage reservoir (FSR) upstream of the city. The FSR halves the annual probability of defences overtopping within the city centre from 1 to 0.5%, achieved through active variable flow control at the FSR. This paper explores some of the challenges faced in the design and construction of the in-river flow control structure which is integral to the operation of the FSR. In particular this paper will consider some of the key environmental objectives for the scheme and offer considerations for working in a dynamic and environmentally sensitive fluvial environment.

Improved drawdown facilities at three flood storage reservoirs

The Hertfordshire and North London Area of the Environment Agency has 18 flood storage reservoirs (FSRs) which come within the remit of the Reservoirs Act 1975. Many have fixed flow control orifices, which cannot be changed when the reservoir is in operation. A review was carried out to determine the ability of the flow control systems to provide drawdown at these reservoirs, considering both the latest guidance on drawdown rates and the ability of the reservoirs to empty quickly to accommodate subsequent floods. The ratio of full storage volume to maximum allowable outflow was used to rank the 18 reservoirs, in order to identify whether investigations into additional drawdown facilities were needed. Three reservoirs were found to require alterations to their outflow controls so that they could provide adequate emergency drawdown. The works required at these three FSRs are described, all of which involve penstocks with differing methods of operation – two being remotely operated.

Three-dimensional modelling at Clays Lake

This paper looks at the three-dimensional (3D) modelling and the benefits and drawbacks that it has, along with how it has been used on the Clays Lake flood storage reservoir and how it was used to improve the efficiency on-site. Clays Lake is one of three flood storage reservoirs on the Upper Mole, which comply with the requirements of the Reservoirs Act 1975, providing flood protection to Crawley town and Gatwick Airport. The reservoir was constructed on behalf of the Environment Agency and was completed in 2019, along with the issue of the preliminary certificate. The dam is formed of a 12 m high earth embankment with a crest length of 120 m. The reservoir has a storage capacity of 385 000 m3 above the permanent lake level. The flow is controlled by an orifice within the main penstock situated at the inlet structure. The main penstock can be opened to release flow more quickly if required. The outlet culvert is 1.8 m in diameter and has fish brushes installed along the invert to aid with fish passage. The downstream embankment slope contains a grasscrete spillway which is overtopped in a one in 1000 year event.

Blue and green infrastructure proposal for an urban watershed in São Paulo to peak flow reduction

The critical issue of floods in Brazilian cities is a consequence of an accelerated and disordered occupation and urbanization process, which results in excessive soil waterproofing, removal of riparian vegetation, silting of rivers and streams, water pollution, among others. In the last decades, the use of conventional drainage techniques has resulted in many problems, due to the fast flow of water to downstream and the pollutant loads that flow to the watercourses. Through Green Infrastructure it is possible to promote urban rainwater storage and infiltration, reducing the probability of flooding, and allowing for the retention of pollutants and consequent improvement of water quality in urban water systems. In this study, the application of Blue-Green Infrastructure (BGI) techniques for the reduction of peak flow and improve the water quality are proposed for the Jacarezinho watershed, located in the Municipality of São Paulo. Hydrological simulations of the proposed solutions indicated a reduction of about 36% of the peak flow, which highlights the relevance of BGI. Unlike the Brazilian conventional drainage that practice the construction of monofunctional flood storage reservoirs (called in Brazil as “piscinões”), the BGI also promotes a harmonious and balanced interaction between the population and the urban landscape.

Civil engineering works versus self-protection measures for the mitigation of floods economic risk. A case study from a new classification criterion for cost-benefit analysis

The application of classical cost-benefit analysis to flood risk mitigation measures can be improved by incorporating new comparative parameters, such as the risk-cost ratio, which is defined here for the first time. In addition, applying these analyses not only to the typical public structural measures (dams, dredging, flood storage reservoirs, transverse drainage works), but also to non-structural measures and self-protection (improving housing resistance to flooding, insurance policies), broadens the range of active risk management options. Last two categories are measures with lower initial investment (thus reducing costs) and visual and environmental impact, making them compatible with the EU Water Framework Directives and flood risk management. All these analyses of economic flood risk have been tested in a small Spanish village in the central Iberian Peninsula. For different flooding scenarios, new proposed RCR criterion allow us a rapid and effective quantification of the efficiency of each of the measures, allowing the ordered classification of the same; as well as the weighting of the results according to the particular needs of the decision makers (prioritizing well the reduction of damages, or the necessary economic investment). Thus, the RCR reveals itself as a powerful tool for flood risk management.

Practical issues in design and construction of dam earthworks

The paper describes examples of common pitfalls in design and construction of earthworks to construct dam embankments retaining large raised reservoirs, focusing mainly on new flood storage reservoirs. It concludes with key considerations for clients, engineers and contractors. It is intended as a briefing to less-experienced colleagues, rather than repeating information in standard textbooks. It is structured to follow the process from initial planning of the source(s) of earthworks through design and construction to operation and maintenance issues.

Preconference tour report: Garstang and Catterall flood alleviation scheme

This paper is an account of the preconference tour of the 19th Biennial BDS Conference 2016. The tour was hosted by the Environment Agency, and took us on a visit to Garstang and Catterall flood storage reservoirs which form part of the flood management system for the River Wyre, Lancashire. Both reservoirs have embankment dams with substantial concrete control structures housing fish belly gates.

Technical visit: Enfield Golf Course flood storage reservoir

In July, the British Dam Society was invited to a presentation and tour of the construction site at Enfield Golf Course flood storage reservoir, north London. The reservoir forms part of the Salmons Brook Flood Alleviation Scheme with the Environment Agency as client, Halcrow (now CH2M Hill) as designer and Volker Stevin as contractor.

Design and construction of improvement works at Bruton flood storage reservoir, Somerset

Following significant floods in Bruton, Somerset during 1979 and 1982, a flood storage reservoir (FSR) was constructed 1·5 km upstream of the town to provide a 100-year standard of flood protection. The storage capacity of the FSR was approximately 500 000 m3 and hence it was covered by the Reservoirs Act 1975. Various studies on the FSR were undertaken between 2000 and 2006 as a result of recommendations made during inspections executed under the Act. The Environment Agency then implemented a £2·5 million programme of remedial and improvement works, commencing on site in March 2008. The works were designed by Black & Veatch Ltd and the main contractor was Jackson Civil Engineering. Construction of the works was completed in summer 2009. The primary drivers for the scheme were the improvement of the spillway and increasing the storage capacity of the reservoir. The opportunity was also taken to construct a new trash screen at the upstream end of the outlet culvert, as the original structure did not meet current standards regarding screen area or safe access. This paper covers some of the interesting features of both the design and construction of the works.

An innovative new spillway for Bruton flood storage reservoir

The Environment Agency implemented a programme of remedial and improvement works at Bruton flood storage reservoir in 2008. As part of the works, an upgrade to the existing spillway was required and this was achieved using a stepped block system designed in accordance with a Construction Industry Research and Information Association special publication. A total of 1869 blocks weighing 900 kg each were needed, presenting a number of challenges, which were overcome through close liaison between the designer, contractor and manufacturer. Despite a tight programme and poor weather conditions over the summer, installation of the blocks commenced in April 2008 and was completed on schedule in September 2008.

Maintenance of flood storage reservoirs

Flood storage reservoirs are generally empty for most of the time and therefore provide some interesting, and often challenging, problems for their effective maintenance. There are a growing number of these reservoirs as the investment into flood risk management infrastructure continues to increase and there are useful lessons to be learned from the design of existing reservoirs and the maintenance issues that they pose. This paper examines some of the principal elements of these reservoirs and the problems affecting their maintenance. It considers how attention to the design or modification of them can provide for improved and more effective maintenance while at the same time affording safer working conditions for those performing the maintenance.

Hydrologic Manipulations of the Channelized Kissimmee River

H istorically, much of 50uthcentral Florida was dominated by a contiguous wetland system that extended from the headwater lakes of the Kissimmee River basin to Florida Bay. During the past half century, this wetland landscape has been compartmentalized with a network of canals, levees, and water-control structures (gated spillways; Figure 1). This network is used to manage hydrologic regimes of the regional hydrosystem, primarily for flood-control purposes (Light and Dineen 1994, Toth and Aumen 1994). Modifications of the physical configuration and hydrology of the South Florida. landscape have affected the Everglades, Lake Okeechobee, and the 7800 km2 Kissimmee River basin, where an extensive flood-control project was constructed from 1962 to 1971. Lakes in the river's headwater basin were connected by canals and partitioned into floodstorage reservoirs; a 90 km long, 9 m deep, and 100 m wide drainage canal

Modelling water quality for urban flood storage reservoirs

The paper outlines a simple modelling basis for estimating the pollutant removal efficiency for flood storage reservoirs receiving drainage water from impervious urban surfaces. The procedure is based on particle-size characteristics, settling velocities of the suspended solids contained in the influent drainage, and consideration of hydraulic retention time within the storage basin. Worked examples illustrate the modelling principles and include details for obtaining overall trap efficiency under both quiescent and dynamic flow for given particle sizes, basin geometry, and inflow conditions. A hydraulic routing algorithm extends the basic procedure to determine mass pollutant outflows from the flood storage basin under varied flow conditions as defined by a typical inflow storm hydrograph. Full details of the algorithm are provided together with a worked example to illustrate the trap efficiency of a storage basin having a controlled outflow and subject to a typical 2-y design storm event.

Book Reviews

Books reviewed in this article: Managing Water as an Economic Resource, by J. Wimpenny. Land Use Planning and the Water Sector: A review of Development Plans and Catchment Management Plans, by S. Slater, S. Marvin and M. Newson. Landscape Specification: Guide to Products and Services for the External Environment. 4th Edition. Edited by C. Robertson. Design of Flood Storage Reservoirs, by M. J. Hall, D. L. Hockin and J. B. Ellis.

Flood Storage Reservoirs: Their Effect on the Power Industry

Flood Storage Reservoirs: Their Effect on the Power Industry