Feasibility Report
MDDP
Tidal Water Resources
Medway Group Abigail Nelson; Agilesh Singaraj; James Robinson; Jessica Hyland; Stavros Kylakos; Thomas Pughe TIDAL WATER RESOURCES | TEAM MEDWAY
Table of Contents
List of Figures ...... 1
List of Tables ...... 1
Executive Summary ...... 1
Introduction ...... 1
Scope of Work ...... 2
Project Context and Goals ...... 3
Summary of Existing Conditions ...... 4
Three Underlying Questions ...... 9
Operational Feasibility ...... 10
Best Configuration ...... 11
How does this compare with other suggested schemes? ...... 13
Conclusions and Next Steps ...... 17
Location of Weir ...... 19
Abstraction Point ...... 23
Mass Balance Check ...... 30
Safety Considerations and Statutory Issues ...... 38
Design Procedure for Movable Weirs ...... 42
Design of Weir ...... 44
Column Calculations ...... 52
Foundation Bearing Capacity ...... 60
Slab Design ...... 69
River Modelling...... 73
Environmental Impact Assessment ...... 92
Hydro-installation ...... 113
Construction Phasing ...... 141
Financial Analysis ...... 147
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Risk Assessment ...... 153
References ...... 159
Appendix A Finance ...... 166
Appendix B River Modelling ...... 169
Appendix C General Scheme Arrangement at Allington Weir ...... 171
Appendix D Guide to Calculations and Relationships for Hydro Unit ...... 172
Appendix E Turbine Locations ...... 175
Appendix F Salinity graphs ...... 180
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List of Figures
Figure 2-1:Location of River Medway ...... 1 Figure 5-1: Rainfall Depths in England and Wales for the past 12 months (Environment Agency, 2014)...... 4 Figure 5-2: River discharge data and predictions for the future (Cloke, et al., 2010)...... 5 Figure 5-3 National Water Resource Availability (Environment Agency, 2000)...... 6 Figure 5-4 Current scheme in place at the River Medway (Beckett, 2014) ...... 7 Figure 5-5 The back pumping scheme that is currently at place for the Medway (Beckett, 2014) ...... 8 Figure 8-1 Downstream of Allington lock at low tide, the area is unnavigable ...... 12 Figure 11-1: Proposed locations of weirs ...... 19 Figure 11-2: Water levels at various locations along the River Medway for MHWS and MHWN ..... 20 Figure 11-3: Location of weir with lock ...... 21 Figure 11-4: Revised location of weir with lock ...... 21 Figure 11-5: Proposed location of weir without lock ...... 22 Figure 12-1 - Medway River with Locations ...... 23 Figure 12-2 - River Medway system diagram ...... 24 Figure 12-3: Map showing the current abstraction point, water treatment works and new potential abstraction point...... 25 Figure 12-4: Map showing Allington weir and position of Burham Water Treatment works ...... 26 Figure 12-5: Extract from South East Water planning drawing for new freshwater pipeline in Burham ...... 27 Figure 13-1 River Medway Schematic for Mass Balance ...... 31 Figure 13-2: Flow for a year for the River Medway at Teston and East Farleigh combined (Taken from Environment Agency, 2014) ...... 32 Figure 13-3: Flow for a year for the River Tesie at Stongbridge (Taken from Environment Agency, 2014) ...... 33 Figure 13-4: Flow for a year for the River Beult at Stiebridge (Taken from Centre for Ecology & hydrology, 2013) ...... 33 Figure 13-5: Flow for a year for the River Medway at Chafford (Taken from Centre for Ecology & Hydrology, 2013) ...... 34 Figure 13-6: First Mass balance principle used ...... 34 Figure 13-7: Second Mass balance principle used ...... 35 Figure 15-1 Schematic of weir ...... 43 TIDAL WATER RESOURCES | TEAM MEDWAY
Figure 16-1 Structural members of the radial gate (Erbisti, 2014) ...... 45 Figure 16-2 Rear view of radial gate showing girder arrangement ...... 46 Figure 16-3 Typical Arrangements of girders ...... 46 Figure 16-4 Segment gate with 2 pairs of arms showing geometry ...... 47 Figure 16-5 Loading on the vertical beams ...... 47 Figure 16-6 Schematic of Floating counter weight showing the concrete filled base ...... 51 Figure 17-1: Plan View of Weir (m) ...... 52 Figure 17-2: Side View of Weir Counterweight and Column (m) ...... 52 Figure 17-3: Column Labelling ...... 53 Figure 17-4: Column design chart (Moss & Brooker, 2006)...... 56 Figure 17-5: Column Cross Section (mm) ...... 59 Figure 17-6: Column Longitudinal Cross Section (mm) ...... 59 Figure 18-1 Borehole locations (British Geological Survey , 2014) ...... 61 Figure 18-2: Weir Dimensions ...... 61 Figure 18-3: Soil Profile ...... 65 Figure 18-4: Pad Foundation Plan View ...... 65 Figure 18-5: Influence coefficients for the increase of vertical stress at points beneath the corner of a uniformly loaded flexible rectangular area (Fadum, 1948) ...... 66 Figure 18-6: Values of Skempton - Bjerrum settlement correction factor 흁 (Skempton & Bjerrum, 1957) ...... 67 Figure 19-1: Foundation Cross Section (m) ...... 69 Figure 19-2: Plan View of Weir (m) ...... 69 Figure 3 Key points in the model shown in the geographical setting (a) and their contribution to the modelled system (b) ...... 74 Figure 47 Modelled Tidal Levels at New Hythe with a neap high tide of 2.38, a spring high tide of 3.58 and a constant low tide at -0.35 ...... 75 Figure 48 Long Section of the River Modelled with drops in river level occur at the two weirs, East Farleigh and Allington...... 76 Figure 49: Schematic of the river model. Dots between object represent river sections ...... 76 Figure 50 The V-(a) and U-(b) shaped river profiles tested ...... 78 Figure 51 River levels along the Medway depths for U-shaped and V-shaped river channel ...... 78 Figure 52 A comparison of gauged and simulated flow (for U-and V-shaped river profiles) between March 10th and April 17th 2012 (Mean Gauged Flow=1.887m3/s) ...... 80
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Figure 53 Comparison of modelled flow rates with different river profiles against gauged flow for high flow rate conditions in winter 2009/10 ...... 81 Figure 54 Natural flow of the River Medway at the point on the river where the moveable weir is to be placed ...... 82 Figure 55 Diagram showing the position of the sluice at maximum and minimum extent (Jessica Hyland) ...... 83 Figure 56 Diagram showing the relative deployment of the sluice gate with the downstream river level ...... 83 Figure 57 The average volume of water abstracted from the Medway for different heights of gate opening for the summer of 2010 (1st June-31st August). Baseline abstraction when the weir is not deployed was calculated as 110.2 Ml/day ...... 85 Figure 58 A comparison of the abstraction volume for various values of the sluice gates deployment depths. The graph compares the different heights at which the sluice gate goes fully into operation and the change of river depth required for the weir to move from being un-obstructive to full deployed. 86 Figure 59 The change of river levels at neap tide with respect to weir deployment heights ...... 87 Figure 60 A comparison of river levels at Lenside and Teston from 20/12/1984 till 30/09/2013 (where data is available for both the Lenside and Teston) ...... 88 Figure 61 an extract of movable Weir for Flows during summer 1976 at the lowest flows of the period compared with flows for the same period during the summer of 2010 ...... 88 Figure 21-1 Key steps in the EIA process (Environment Agency, 2002) ...... 92 Figure 21-2 Hierarchical Mitigation Process (Environment Agency, 2002) ...... 93 Figure 21-3 The Medway Estuary (Wildlife-Trust, 2006) ...... 95 Figure 21-4 Critical periods for fish species in the Medway Estuary. Data from (Environment Agency, 2013) ...... 102 Figure 21-5 Medway Estuary divided into smaller ecosystems (Medway Council, 2011) ...... 104 Figure 21-6 Cattle grazing near Allhallows at the Medway estuary (Medway Council, 2011) ...... 104 Figure 21-7 Typical river profile with regards to salt and fresh water interactions (Oberrecht, 2010) ...... 106 Figure 21-8 Salt-Wedge estuary with a sharp density interface boundary layer (shown in red) ...... 106 Figure 21-9 Assumed layout of the impounded fresh and salt water ...... 107 Figure 22-1 Proposed Site Locations (Google Maps, 2014) ...... 114 Figure 22-2: Allington Weir (Geograph, 2013)...... 115 Figure 22-3: Allington Weir and Lock Exit (unknown boater, 2001)...... 116 Figure 22-4: Representation of an Archimedean Screw Turbine (Kalkani & Stergiopoulou, 2013). 118
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Figure 22-5: Representation of an axial-flow Kaplan Turbine (Renewables First, 2014)...... 120 Figure 22-6: Efficiency change against increasing flow by turbine type (Mann Power Consulting Services, 2008)...... 121 Figure 22-7: Flow Duration Curve for Allington Weir...... 126 Figure 22-8: Head Duration Curve for Allington Weir...... 127 Figure 22-9: Water Level Duration Curve for the movable weir during winter...... 129 Figure 22-10: Flow Duration Curve for the movable weir during summer...... 130 Figure 22-11: Head Duration Curve for the movable weir during summer...... 131 Figure 22-12: Flow/head duration curve for the comparison of flows for different sizing options. .. 133 Figure 22-13: Energy capture duration curve for different sizing options...... 134 Figure 22-14: Flow/head duration curve for the comparison of flows for different sizing options. .. 135 Figure 22-15: Energy capture duration curve for different sizing options...... 135 Figure 23-1: Site Access ...... 141 Figure 23-2: Current Site Users ...... 142 Figure 23-3: Choosing a method for isolating a works area in rivers (Scottish Environment Protection Agency, 2009) ...... 143 Figure 23-4: Cofferdam installation from marine barges (The Mersey Gateway, 2014) ...... 144 Figure 23-5: Partial river isolation/ cofferdam (Scottish Environment Protection Agency, 2009) .... 145 Figure 23-6: Partial isolation using a caisson (Scottish Environment Protection Agency, 2009) ...... 145 Figure 23-7 Construction Phasing ...... 146 Figure 26-1 High tide at high abstraction levels ...... 180 Figure 26-2Low tide at high abstraction levels ...... 180 Figure 26-3 High tide at low abstraction levels ...... 181 Figure 26-4 Low tide at low abstraction levels ...... 181
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List of Tables
Table 9-1: Southern Water's costings for their proposals in the future management of their water resources (Adapted from (Southern Water, 2014, p. 181))...... 15 Table 10-1 Design Consideration Checklist ...... 17 Table 13-1 Initial Abstraction and River flow values ...... 31 Table 16-1 Calculations for Hydrostatic Forces (All equations from (Erbisti, 2014)) ...... 44 Table 16-2 Vertical Girder Calculations Equations from (Erbisti, 2014) ...... 47 Table 16-3 Calculations for Radial Arms (All equations from (Erbisti, 2014)) ...... 49 Table 16-4 Calculations for counterweight Design (All equations from (Erbisti, 2014)) ...... 49 Table 17-1: Cover Requirements (BS EN 1992-1-1:2004, 2004) ...... 54 Table 17-2: Recommended Structural Classification (BS EN 1992-1-1:2004, 2004) ...... 55 Table 18-1: Borehole Data (all data obtained from British Geological Survey (British Geological Survey , 2014)) ...... 60 Table 18-2 Drained bearing capacity factors (Woods & Matthews, 2013) ...... 62 Table 18-3: Borehole Data (British Geological Survey , 2014) ...... 64 Table 19-1: VRd,c resistance of members without shear reinforcement, MPa (Brooker, 2005) ...... 71 Table 2 Modelled Cross Sectional Flood Levels for Annual Exceedance Probability shown in mAoD (Data is obtained from the Environment Agency) ...... 78 Table 15 Error in model under drought conditions ...... 80 Table 16 Error in model under drought conditions ...... 81 Table 17 A comparison of Abstraction volumes for projected flow conditions for two summer conditions ...... 90 Table 6 Summary table of the environmental factors which are impacted in the Medway estuary ..... 96 Table 21-7: Environmental Impact Assessment ...... 108 Table 22-1 Generator Mechanism Sizing Options ...... 124 Table 22-2: Tariff Rates for Hydroelectricity (Energy Saving Trust, 2014)...... 138 Table 3: Capital costs of the project ...... 147 Table 4: Energy saving cost ...... 149
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Executive Summary
The South East of England is experiencing a shortage in the supply of water, due to high demand and low rainfall compared to other regions of the UK. There are currently multiple solutions being suggested, including desalination, increasing the capacity of the regions reservoirs and other novel ideas. This report will investigate the feasibility of installing a movable weir in the River Medway to impound tidal water.
The River Medway provides water for Southern and South east water companies. Currently water companies pump water from two abstraction points back to Bewl to maintain the natural flow of the river whilst abstracting water for potable uses further downstream this pumping costs water companies in the region of £0.5M per annum. The weir is to be placed downstream of the terminal weir in the tidal section of the river.
The key factor for ensuring that the movable weir is an effective solution to this problem is the amount of water impounded and subsequently the location along the river reach. Once this was determined the design of the weir was carried out and a river model produced using the software package ISIS, this showed the effect the weir will have on the current river conditions and how the weir will cope with future water demand. These studies allowed an environmental impact assessment to be conducted, this investigated the impacts a new weir would have on the estuary and surrounding areas, allowing mitigation to take place during the design phase. As the project is concerned with the amount of energy used to pump water back up to Bewl and the amount of carbon this releases, an investigation into a hydro power unit was carried out. Due to the relatively low flow rates and inadequate hydraulic head, it was decided to investigate a small scale run of river scheme involving an Archimedean screw generator.
The weir designed in the following report impounds water that is the equivalent of the amount of water currently pumped back to Bewl and is also future proofed, the weir does not affect the navigability of the river as it has been moved downstream to prevent the need for a lock, which would disrupt the local area less. The design of the movable weir means that a fish pass in not necessary.
The weir is based on a Taintor gate design but is moved by a system of floats rather than a mechanical system which would require an external power source. The weir has floats at either end which are in concrete housing to protect them from bow waves and other minor disturbances
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We recommend that further work is carried out before the project is taken any further, these include, a site visit and investigation, full geotechnical survey, seek planning permission and licences from the Medway Council, public opinion survey and maintenance schedule for the weir and possible hydro unit.
The model should be updated as more relevant data becomes available from the site investigation this would allow a more thorough water quality analysis within the environmental impact assessment. The weir could also be modelled physically to be tested in a flume, which would show how it reacts to real life situations.
From the evidence provided in this feasibility report, placing a movable weir in the river Medway to impound tidal water and reduce pumping costs and associated carbon emissions is feasible, socially, environmentally and economically. The money spent building the weir will be recuperated after 9 years of operation with the hydro unit producing electricity to be sold to the national grid and the saving from not needing to pump water back to Bewl reservoir.
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Introduction
Water is a finite resource, vital to human existence and fundamental to the way we live. An assured supply of potable water patterns and stricter regulations on the environmental impact of water usage have demonstrated the vulnerability of this supply. The availability of fresh water is of no more concern than in the south east, the driest region in the country, with some areas getting less rainfall than parts of the Mediterranean.
Figure 2-1:Location of River Medway
The River Medway is situated on the eastern side on the south east region, where rainfall levels are even lower than areas to the west (Medway Council, 2008), it currently supplies water for 25% of the population in the Kent Medway region (Southern Water, 2014). The water from the River Medway is used for both water treatment at Burham and for topping up Bewl reservoir during periods of heavy rainfall. Water is pumped from Yalding to Bewl (approximately 12 miles away) which requires round £0.5m/year for electricity. The water at Bewl in the summertime period is used not only to provide water to the surrounding population but also to maintain the natural flow of the river. Since pumping the water upstream is energy intensive and cost ineffective and losing the water over the terminal weir at Allington is a waste of freshwater, an alternative is highly desirable.
A plausible method would be to impound a volume of tidal water equivalent to that abstracted by the water companies between the terminal weir at Allington and a new movable weir downstream which would allow the natural flow of the river to be maintained. As the weir is movable, it can be deployed when needed but create no interference with river flow when not required. This would mean that instead of releasing the water from the reservoir at the top of the estuary, it would be released from the temporary storage pound at the top of the estuary, at a steady rate over the low tide period, thus ensuring the correct flow at all times and mitigating the need to pump water back up to Bewl.
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Scope of Work
The feasibility study of the proposed movable weir will include the following tasks:
Evaluation of the river model with the aim to provide data on the effect of installing a movable weir on the water quality with regards to salinity and oxygen content and its effect on the flow of the river Medway. Providing an environmental impact assessment for the river sections affected by the proposed movable weir. In particular the effects on the surrounding ecosystem. The consideration of the ecological impact of the weir and how to mitigate them with methods such as fish passes. The effect of the weir on the current users of the waterway. Design of the weir including the static and movable components. Proposed construction methods and procedures. Evaluate the proposed energy and water savings with the proposed movable weir in comparison with the current water management system. Provide details on the financial costs with regards to constructing and running the proposed movable weir. To assess the feasibility of the use of a hydro unit to provide power from our installation.
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Project Context and Goals 4.1 Project Context
Water should be made use of where and when it is available. Currently there are two options when it comes to improve water resources; reducing the total amount of water we use or increasing the availability of potable water. In the River Medway, fresh water is being used to keep the natural flow in the river. This project will look into how the tidal water in the estuarine part of the river can be used to keep this flow, so that the fresh water can be used in a more productive manner.
4.2 Project Goals and Objectives
In considering the feasibility of a movable weir in the River Medway the following goals were established:
Determine if the weir can physically be constructed Determine if it is operationally compatible with existing water usage and will its addition reduce pumping Determine the financial and environmental impacts on stakeholders.
The study was guided by the following objectives:
To make the most effective and efficient use of water that is available where it is available To be as independent of the climate and weather as possible To reduce dependence on electricity To be economic to implement To minimise environmental impact This feasibility study investigates one possible solution to the lack of water in the South East of England. Other such solutions can been seen in State of Medway Report: Water Supply (Medway Council, 2008)
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Summary of Existing Conditions 5.1 Water Resources in South-East England
As also mentioned in the 8th report of the House of Lords and Technology Committee, in 2006, it is expected that over the following years, water resources in South-East England are going to be further pressurised due to an increase in changing climate and extreme weather events, population growth and regulation constraints on protecting the ecology. As a result, if the configuration of an organised strategy is not attempted, it is very likely that the reducing volume of potable water is not going to be adequate in meeting the potentially increased demand.
In the same report from the House of Lords Science it is stated that “water resources are threatened by below average rainfall in the short-term”. The map/graph below, presents UKPP radar data of monthly rainfall depths across England and Wales for the past 12 months (November 2013-October 2014). As it can be identified, rainfall depths shown around the area of River Medway and South-East England in general are relatively low in comparison to the rainfall depths measured in the rest of the map.
Figure 5-1: Rainfall Depths in England and Wales for the past 12 months (Environment Agency, 2014).
Climate changes are expected to stretch the time period in which rainfall depths fall below average, increase the frequency of sudden flooding (during winter months) and overheating followed by low flows (during summer months) . Consequently, climate change is going to impact river abstraction
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depended sources as river flows will decrease significantly during specific time periods, leading to restrictions in obtaining the required amount of water in order to maintain a balance. As a big amount of public supply is freshwater sourced in rivers, reductions in potable water availability, especially during the summer, frequent and extensive water regulation constraints and potential water shortages are likely (ClimateUK, 2012). The graph below shows the past, current and estimated future flows for the River Medway at Teston and below.
Figure 5-2: River discharge data and predictions for the future (Cloke, et al., 2010).
In the South-East, the amount of water abstracted from the environment is very close to the amount being available. Therefore, there is not much room for big improvements of the existing system nor for further exploitation of water resources. For many areas such as at River Medway, the level of authorised abstraction could reach more than ¾ of the effective rainfall in an average precipitation year. In an average year, the water volume abstracted from both surface freshwater and groundwater sources is proportioned as 80% of the total abstraction volume. Even for under average precipitation conditions, the total demand for the South-East region accounts for 5,410 of the 5,500 Ml/d water supply availability. As it can be seen in the figure below, the South-East region is deemed to have an unsustainable abstraction regime during winter but especially during summer months (Graham, 2007).
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Figure 5-3 National Water Resource Availability (Environment Agency, 2000).
This shows that even with the current demand growth, the volume of water available for public supply would not be adequate in a few years’ time, even for under average precipitation conditions. Currently, standards of service require companies to keep a minimum supply volume of 10% to 15% higher than the average (6,200 Ml,d). At this point, the total housing growth water demand increase for the South- East is estimated to be 120 Ml/d for at least until 2025 (Graham, 2007).
The current scheme in place at the river Medway enusures that the natural flow of the river is maintained by allowing freshwater to crash over the terminal weir at Allington. Maintaing the natural flow of the river down into the esturay is a key feature and usage of the resevoir at Bewl. The current scheme is shown in Figure 5-4 Current scheme in place at the River Medway .
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Figure 5-4 Current scheme in place at the River Medway (Beckett, 2014)
These are the existing conditions and usages of the terminal weir at Allington however with the inclusion of a new movable weir downstream the need for allowing usable freshwater to overflow Allington weir will hopefully be removed. Therefore the freshwater that is currently being used to maintain the natural flow of the river may be used for other sources such as water supply. This is the existing conditions at Allington weir that will hopefully be improved upon the inclusion of a new movable weir downstream.
In order to maintain the level of water in Bewl reservoir the existing option that is currently in use is to back pump freshwater from the river Medway at various pumping stations along it. This is shown in Figure 5-5.
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Figure 5-5 The back pumping scheme that is currently at place for the Medway (Beckett, 2014)
Figure 5-5 The back pumping scheme that is currently at place for the Medway shows that water is pumped back from Yalding pumping station and from Small bridge pumping station. The natural inflow of water into Bewl reservoir is only 20% (Beckett, 2014). Therefore the pumping is required to this extent with the current existing conditions. The back pumping that is done currently costs more than £500,000 per year just for the electricity (Beckett, 2014). The CO2 that is also produced as a by- product for pumping the water is also a vast amount. It is predicted that with the inclusion of a new movable weir downstream the existing conditions would change immensely, this includes an electricity reduction cost of around £250,000 and a CO2 decrease of around 1800 tonnes. (Cutting, 2014)
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Three Underlying Questions
The feasibility study set out to answer three fundamental questions:
1. Is the addition of a movable weir in the River Medway operationally feasible?
2. Which weir configuration provides the best water efficiency with the least economic, environmental, and social impact; including the reduction of greenhouse gasses?
3. How does this compare with other suggested schemes in respect to the efficiency of water usage?
Analysis indicates that, from an environmental, social and economic perspective, constructing a movable weir is operationally feasible. Furthermore, initial planning and design demonstrates that the movable weir and its associated improvements can be accommodated on the site and that if constructed, it has the potential to increase fresh water available for abstraction and reduce the costs and carbon associated with pumping water back to Bewl Reservoir
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Operational Feasibility
In order to determine if constructing a new movable weir downstream of Allington Lock was operationally feasible two components were evaluated:
Will the proposed movable weir operate effectively Is the proposed movable weir a viable alternative to the expansion of Bewl water
7.1 Weir Operation Feasibility Analysis
By installing a movable weir downstream of Allington the aim is to make the most effective use of the water that is available.
The proposed weir operates by capturing the required volume of tidal water downstream of Allington Lock which is then gradually released to maintain the natural flow in the Medway Estuary. As tidal water is being used this is saving this volume of fresh water that could now be used within the mains water network.
Because currently every day 180ML needs to be used to maintain the natural flow, this water has to be taken out of Bewl Reservoir. As this amount of water is saved, the volume of water that needs to be pumped to refill Bewl is reduced. This reduction in pumping not only saves on pumping costs to the order of £0.5 million, but consequently will also reduce the greenhouse gas emissions.
7.2 Effective Solution Analysis
There are many alternative projects currently undergoing feasibility and planning stages, the reasons why the proposed weir is likely to be more affective is as follows.
As the weir would only require a minimal amount of land to be constructed this will reduce the cost for purchasing the land and will reduce the local environmental damage due to the fact that the area will experience a relatively minor alteration to the ecology when compared to the construction of a new reservoir.
Because the extent of the disturbed environment is greatly reduced this will make it much more likely to obtain planning permission. Hence the amount of time that this project is in the planning stages will be greatly reduced therefore reducing the cost associated with the planning phase of construction.
The installation of the weir would be a viable option due to the fact that it would be considerably cheaper than any current proposal to expand or build a reservoir.
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Best Configuration 8.1 Environmental
The weir has been designed to maintain the natural flow in the river during dry periods this will ensure that the ecological system of the river remains unaffected by water abstraction further upstream. The weir itself is self-regulating on a system of floats and counterweights, this scheme requires no external power input, thus giving it a neutral carbon footprint. A hydropower unit included in the scheme allows for clean power generation and offsets any carbon emissions during the construction phase. A reduction in the amount of pumping required means a saving in energy usage and greenhouse gas emissions.
8.2 Economic
As the weir is designed to be self-regulating there is no need for a power input to operate it, this reduces the energy costs over the life of the weir. The nature of the weir also means that it does not need to be manned at all times but rather monitored occasionally to check its condition and to disable it during wetter periods. Potential inclusion of a hydro-power unit will provide income as the electricity is supplied to the national grid the unit could be used all year round to provide a constant supply of energy. The scheme also incorporates moving the current abstraction point at Springfield closer to Allington this will improve the efficiency of pumping by pumping over a smaller distance.
8.3 Social
The chosen location of the weir means that a smaller head of water is impounded, this means that current navigation rules are not affected. This allows people who use the river for recreational purposes to be unaffected by the weir as it is only used when the river is closed for navigation.
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Figure 8-1 Downstream of Allington lock at low tide, the area is unnavigable
The weir is located in an area of industrial space, there are no residents for the weir to effect. This allows for disruptions due to construction to be minimised or even non-existent. The use of local businesses and materials for weir construction allows the surrounding area to prosper from the manufacture of the new structure.
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How does this compare with other suggested schemes?
The aim of our weir design is to be a method of increasing water supply to ensure a reliable source of water for the Maidstone Medway. However, in order to validate that the proposed method is a viable solution its suitability must be compared alternative methods of increasing water supply. In its water management plan (Southern Water, 2014, p. 181) Southern Water have already drawn up a list of possible options (each involving several of increasing supply) to ensure they are able to continue to effectively supply water to its customers in the future. As a consequence it will be vital to demonstrate that our proposed scheme can improve these current options by adding a method of increasing supply that is not only cost effective, but reliable in the long term with a low carbon and environmental footprint.
9.1 Suggested Schemes
All the schemes that have been stated can be found in the 2008 State of Medway Report in the water supply section and on the Southern Water and South East Water company websites and reports.
Possible Schemes suggested:
Desalination Resource increase from abstraction outside the Medway area Increase and improve the supply through pipes by leakage detection and repair strategies, South East Water have stated that it costs £13 million a year to undertake Introduction of water meters at both domestic and commercial properties this will be undertaken without technical constraints Variation in the surface and ground water licences that will enable a daily rate of abstract over the whole year Reservoir raising To reuse 20Ml/d of treated wastewater that is returned to the Medway to be abstracted further downstream Water Efficiency audits to encourage water savings for homes, schools and businesses aiming to reduce usage by 10% Asset enhancement schemes by connecting isolated reservoirs with pipelines to add flexibility Catchment management changes, including reduction of nitrate pollution in water supply allowing for more useable water
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Upgrading boreholes and creating new borehole sources Development of existing groundwater source New service reservoirs
There are several different factors that need to be assessed when considering how implementing the scheme we prose compares to the
The cost of implementation The increase in water supply (or decrease in demand) generated The direct environmental impact of the scheme The carbon footprint and energy use of the project, both during construction and during its operational lifetime Speed of implementation
These factors have been discussed below in relation to the schemes that have been proposed
Raising of reservoirs may have the potential to significantly increase water supply the can be produced from Bewl, with some similar projects under consideration allowing for a 35% increase in capacity (BBC, 2011). In its environmental impact assessment (Southern Water, 2014, p. 187), raising the reservoir levels would have a significant environmental impact on the environment. It would require destruction ancient woodland around reservoirs such as Bewl as well as potential for protected species being affected as well due to habitat destruction. The changes may also have negative impacts on the ecology of the reservoir which would have to be mitigated. Furthermore it also fails to address the issue of reducing the carbon footprint of water, as it will require an increased level of pumping to fill the reservoir. In addition, plans for asset enhancement including adding new pipelines to connect isolated reservoirs, to provide more flexibility also require an increase in pumping, hence requiring an increase in energy use. A further aspect of this is the proposal to amend southern waters abstraction license to allow more water to be abstracted from the Medway and pumped Bewl during wet weather which also suffer similar issues.
Making better use of water resources is also a potential solution. Methods to reduce pollution from nitrates, allowing for more usable water to be retrieved along with water reuse through the treatment of waste water was another potentially large source of new water potentially is recommended by southern water. The latter option is claimed to have the potential to provide up to an extra 20Ml/day to start coming into operation by 2022. Comparing this with the potential extra abstraction possible with the proposed scheme of between which even in a 1979 style drought projected forward to 2050-2080,
GROUP HOW DOES THIS COMPARE WITH OTHER SUGGESTED SCHEMES? PAGE | 14 TIDAL WATER RESOURCES | TEAM MEDWAY abstraction of 18Ml/day could be seen, or just under 60Ml/day in regular summer conditions in the period 2050-2080. Gains from leakage reduction, whilst only account for increases of around 0.5- 5Ml/day may also be relatively expensive costing around £13 million to implement.
There are also several non-infrastructure based approaches including getting consumers to reduce usage by a predicted 10% which seem like effective, with little or no associated carbon footprint. However, these measures are limited by an increase in population predicted in the south east. They are also
Finally, the option of desalination, whilst considered by southern water in other areas was not proposed as an option in southern waters eastern regions, which includes the Kent Medway. Overall this suggested that the company consider that this is either not suitable or not feasible for increasing water supply. One obvious barrier to this is disruption to wildlife that may be caused in the salt marshes at the outermost reach of the Medway estuary, with several nature reserves in the area. Some of the above schemes will be done in conjunction and for Southern Water there are various combinations of the proposed schemes with pricings as shown in Table 9-1 below.
Table 9-1: Southern Water's costings for their proposals in the future management of their water resources (Adapted from (Southern Water, 2014, p. 181)).
Proposal Scenario Total Cost with NPV discounted over 80 years (£) Asset enhancement schemes, catchment management, 65,365,000 licence trading scheme, minimal leakage reduction, groundwater licence variation, Water Efficiency audits and water reuse. River Medway licence variation, Asset enhancement 61,428,000 schemes, Catchment management, Licence trading schemes, Water Efficiency audits and Water reuse. Minimal leakage reductions, Catchment Management, 62,761,000 Licence trading scheme, River Medway licence variation, Groundwater source licence variation, Water efficiency audits and Water reuse. Reservoir raising, Asset enhancement schemes, 60,630,000 Catchment management, Comprehensive leakage reductions, River Medway licence variation, Licence trading scheme, Water efficiency audits and Groundwater source licence variation. Asset enhancement schemes, Water reuse, Catchment 60,879,000 management, Comprehensive leakage reductions, River Medway licence variation, Groundwater source licence variation and Water efficiency audits.
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Although our scheme increases the water efficiency and reduces the carbon usage for the water companies it does not solve all of the issues that relate to water efficiency. For example a major problem in the efficiency of water is that of leakage through the pipes used in the transportation of water, whether it is raw or potable.
In terms of future efficiency with the increase of demand expected to grow the addition of movable weir to impound water will improve the situation. The movable weir will also be able to put into place in a reasonable about of time and will affect the supply efficiency noticeable as soon as it has been implemented unlike many of the other schemes which will be rolled out over a 45 year period.
Obviously all of the schemes depend on the funding that can be obtained and as this is a feasibility study the addition of a movable weir has yet to acquire funding and approvable by the Government unlike those proposed as shown in Table 9-1 where these schemes have gone before Government. In terms of cost however, the installation has a relatively low cost when compared with the other proposed schemes. Therefore, on a monetary and efficiency bases it gives best value for money.
However, the addition of a movable weir does not solve the problem of water shortage in the south east and it will take the implementation of other proposals particularly the reduction of leakages to that will start to reduce the problem. But with climate change the need for greater water supply will only be increased and then there is a clear requirement for all the proposals to be executed to relieve the burden on the current situation.
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Conclusions and Next Steps
Table 10-1 shows the areas that need to be considered when designing and installing a new weir
Table 10-1 Design Consideration Checklist
General Considerations Design Issues New weir Hydraulic design Is the weir really necessary? Flow range in river. Design maximum Have alternatives to a weir been flow considered? Impact on water levels throughout flow Refurbishment of weir range Is there an opportunity to improve the Impact on flood risk weir for fish, canoeists, amenity, and/or Check that hydraulic jump is always in environment? stilling basin Removal of a weir Safety issues Have all of the potential impacts been Public safety assessed? Safety of boaters and canoeists Consultation CDM Regulations Identify all stakeholders and interested Operation and maintenance activities parties Need for warning signs, fencing, life- Fundamentals saving equipment Ensure that the objectives of the project Safety during construction are clear Structure Surveys and investigations Design to prevent bypassing in floods Gather all available data on flows and Check sub-structure for uplift levels Need for erosion protection on bed and Topographic survey of the site and banks environment Stability and durability in flood flows Environmental baseline survey Choice of appropriate fish pass if Hydrometric (flow monitoring) weirs needed Suitable approach flow conditions Ground/structural investigation Sufficient head across weir in all flow River corridor survey conditions Consultation with fisheries officer Choice of appropriate weir type Establish land ownership Sediment/weed growth problems Recreational use of river canoeing, Temporary diversion of footpaths angling, etc.) Opportunities Historic / archaeological survey Improvements to local habitat Investigate access routes for Remove barriers to fish migration construction Improved conditions for wildlife Legal and planning Improved conditions for canoeists Navigation rights on river Opportunities for hydropower generation Are any rights of way affected Land drainage consent SSSI, SAC, AONB Is planning permission needed?
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Environmental Issues Operational issues Potential impacts Safety of O&M personnel Disruption/loss of fish migration and Need for lighting at the weir site spawning Assessment of likely trash/debris load Damage to local landscape Facilities for debris removal/storage Effect on local groundwater regime Safe access to all parts of the structure Loss of historic/heritage value Need for periodic removal of sediment Local wildlife (otters, birds, Operating plan when weir or equipment invertebrates) fails Local residents (noise, view, access Maintenance plan and schedule rights, etc.) Maintenance equipment needs Land acquisition issues Environmental design Landscape design Appropriate materials/finish/colour Potential to improve habitat variety Current/future water quality constraints Appearance in low flows Geomorphological issues Sedimentation (new weir) Scour of upstream sediment (demolition/lowering) Scour downstream of a new weir Pollution control during construction Timing to minimise impact (fish, birds, river users) General disturbance to established habitats Noise during construction Access for construction Temporary works (e.g. flow diversion) Public safety/information (fencing, signboards, etc.)
In the rest of this report detailed studies into the areas ticked above can be found, before further work can be carried out and the project completed the other areas need to be investigated so as to ensure a smooth running project. As this report is a feasibility study some of the points above were deemed inappropriate for this level of investigation.
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Location of Weir
As tidal water will be impounded (levels of water shown in Figure 11-2; these levels were used in the estimation of the position of the weir) and the River Medway is a navigable river a problem arises with the effects of placing a weir to the other users of the waterway in particular boats. Therefore two options have been studied, one where a lock will be required for passage of vessels, the other where the weir deployed at such a point so as to not interfere with the vessels. Below is the location of the three proposed weir positions.
Proposed location 3
Proposed location 2
Proposed location 1 Allington Lock
Figure 11-1: Proposed locations of weirs
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Water Levels for Mean High Water Springs and Mean High Water Neaps from Allington Weir to the sea
3.7 3.5 3.3 3.1 2.9 2.7 2.5 2.3 2.1
Water Level Level Water(m) 1.9 1.7 1.5 Allinton New Hythe Wouldham Rochester Chatham Bee Ness Sheerness Lock MHWS 3.58 3.55 3.49 3.26 3.3 3.2 2.9 MHWN 2.38 2.35 2.29 2.16 2 2 1.8 Port Name
MHWS MHWN
Figure 11-2: Water levels at various locations along the River Medway for MHWS and MHWN
11.1 Proposed location 1- Lock required
Our initial proposal would require the installation of a lock to ensure this stretch of the River Medway remains navigable. The benefit of this method would mean that the weir would be deployed at high tide and would reduce the distance the weir would need to be from Allington, therefore disturbing a lesser length of the river.
The initial proposed location for the weir can be seen in Figure 11-3 however this location is right near a built up area and therefore it is recommended that the weir is placed 200m downstream because this is a far less built up area and would reduce the difficulty of obtaining planning permission. The new location can be seen in Figure 11-4.
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Figure 11-3: Location of weir with lock
Figure 11-4: Revised location of weir with lock
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11.2 Proposed location 2
Our alternative proposal would not require the installation of a lock. The weir would be placed further downstream and would capture the tidal water at half-tide, thus enabling boats passage to the estuary without the need for a lock. The position of this weir was calculated using the opening times for Allington lock; which are 3 hours before high tide and two hours after high tide; and half the maximum speed at which the boats can travel along the estuary to ensure they can cross the weir before it is deployed. This speed used for these calculations is 3 knots.
The proposed location; which can be seen in Figure 11-5; is 4.3km downstream of Allington weir, the reduced depth the water caught on a neap tide (worst case scenario) however wouldn’t allow the vessels with a draft greater than 1.2m to pass our weir 3 hours after high tide. Though this is not an issue due to the fact that a vessel with a draft greater than 1.2m would have to leave Allington at high tide anyway otherwise the river currently wouldn’t be deep enough for these vessels.
Figure 11-5: Proposed location of weir without lock
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Abstraction Point 12.1 Location of current abstraction point
Currently the abstraction point that is used by both Southern Water and South East water that is situated at Springfield for the Burham Water Treatment plant (as shown in the figures below). Springfield if situated by Allington which is the last point for fresh water abstraction before the terminal weir and the river becomes estuarine.
Figure 12-1 - Medway River with Locations
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Yalding Springfield River Abstraction Abstraction Continues to point point the Estuary
Teston Weir Allington (gauging Weir station)
Figure 12-2 - River Medway system diagram
12.2 Issues surrounding its current location
In this location when the second movable weir is added the water between the abstraction point and Allington weir will be stagnated as the normal flow of the river will not be kept. To rigidify the situation there are several solutions. This stagnation occurs because the abstraction further up river is kept at its normal rate.
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Burham Water Treatment Works
Allington Weir
Springfield Abstraction point
Figure 12-3: Map showing the current abstraction point, water treatment works and new potential abstraction point.
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Burham Water Treatment Works
Allington Weir
Figure 12-4: Map showing Allington weir and position of Burham Water Treatment works
12.3 Potential locations
Taking out the abstraction point at Springfield and pumping water from Allington straight to Burham Water Treatment works. There are three potential pipes that can be added to move the water the new abstraction point to the Burham water treatment works.
12.3.1 Solution one South East water are currently undergoing plans to add in more pipes to take water from Burham water treatment plant across the Medway River to meet the supply demand in the South East region. The pipe locations could be used to place new pipes in the same location for the transportation of the raw water. Figure 12-5 shows the planning drawing for one of the new potable water pipeline from Burham to increase its distribution throughout the surrounding area by South East water.
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Figure 12-5: Extract from South East Water planning drawing for new freshwater pipeline in Burham
To do this it would require all new lengths of pipe to be installed, it will therefore increase the cost of the addition of the weir in the River Medway. For this the cost would be increased by the price of the pipes and the cost of installation.
Currently South East water are planning on using pipe with an internal diameter of 600mmm. To work out the pipe diameter needed, which can be used in all the proposals, can be calculated by the following equation.
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푑 2 푄 4 푄 = 3600휋 × 푣 ( ) → 푑 = √ 푊 × 푊 2 3600푣 휋
Where; d= pipe inner diameter, v=water velocity and Qw is water flow rate.
The volume of water abstracted at Springfield that goes to Burham 522000m3/s, using a water velocity of 10m/s. Therefore the diameter of pipe needed is 1.273m which is 1275mm.
A major issue with this solution is the carbon usage that would be incurred. The carbon usage comes threefold in the casting of the pipes, the transport and laying of the pipes and the transportation of the water with the pipeline system.
12.3.2 Solution two Another possibility is to connect to the pipeline that already exists taking water from Springfield to Burham Water Treatment works, this would be done by the addition of a new pipe from Allington to connect it with the pipe that runs from Springfield. This solution would reduce the carbon footprint of the water companies as it reduces the length of pipe already in place as Allington is closer to Burham Water treatment plant than the Springfield abstraction point. Of course there would be the initial outlay cost of install a new pump and pipeline at Allington that would be connected to the existing pipeline but this solution in balance is the most cost effective and using the least carbon in the long run.
12.3.3 Solution three A final possibility for changing the abstraction of water is to pump water from Allington back to Springfield to then use the existing pipeline to transport it to Burham. This would involve installing a pump and pipeline to connect Allington to Springfield and then a connection from that new pipeline to the existing pipeline. An issue associated with this solution is that it is energy intensive and therefore would increase the carbon usage of the water company and would defeat the reason why a feasibility study is being undertaken to introduce a movable weir.
12.4 Conclusions
In terms of Carbon usage reduction solution two is the best possible solution as the carbon usage in the construction phase is lowest and it would require the instillation of the least length of pipes.
From initial investigations there does not seem to be any issues with the moving of the abstraction point however moving forward from this feasibility report a more rigorous investigation needs to be undertaken to determine whether there will be any potential problems with the water abstracted at
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Allington. If it is found that the water here requires a heavy cleaning process then there will be an incurred cost additional to the initial project cost from the changes required at the treatment works.
12.4.1 Cost By looking at the cost estimated for the new 7km supply pipes being installed by South East water it would be estimated that the cost of moving the abstraction point would be around £0.75million.
The cost includes:
the construction of a new abstraction stations and pump including material costs the installation of the pipeline ( the placing and buying of materials) the connections of the new pipeline to the existing pipeline labour and permit costs
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Mass Balance Check
A Mass Balance assessment was undertaken to evaluate whether the placing of a movable weir in the River Medway will balance out the water abstracted which will allow Bewl reservoir to be keep at a higher level as water will not have to be released to keep the natural flow of the river. Therefore the stretch of the River Medway including the tributary with Bewl down to the Estuary was considered as shown in the systematic figure below. The values used in the assessment for river flow rate and abstraction rates as shown in Table 13-1; both the peak flow and the minimum in the summer months has been used in the calculations and were taken from the graphs shown in.
From the analysis the water held in the reservoir created by the movable weir balances that of the total abstracted water as the total sum of the abstracted amount currently is less than that of the water held by the weir. By holding water at the movable weir the abstraction points at Small Bridge and Yalding can be removed stopping the pumping of water from these points to Bewl Water which will save the water companies involved between £0.5 and £1 million a year in energy costs. The removable of the need for these points will be met in the movable weir and thus will also reduce the carbon usage of the water companies.
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Estuary
Proposed Weir
Allington Weir
Springfield
Teston
Yalding River Medway River Beult
Small Bridge
Bewl
Figure 13-1 River Medway Schematic for Mass Balance
Table 13-1 Initial Abstraction and River flow values
Position River Flow – Discharge Abstraction Rate (m3/d) (m3/d) River Teise 86400 25920
Small Bridge 8000
River Medway - Upper 77760 21600
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River Medway - Lower 691200 216000
Yalding 13000
River Beult 17280 4320
Springfield 522000
Total 543000
Key: Summer Peak Flow, Summer Minimum Flow
13.1 River Flow graphs
Figure 13-2: Flow for a year for the River Medway at Teston and East Farleigh combined (Taken from Environment Agency, 2014)
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Figure 13-3: Flow for a year for the River Tesie at Stongbridge (Taken from Environment Agency, 2014)
Figure 13-4: Flow for a year for the River Beult at Stiebridge (Taken from Centre for Ecology & hydrology, 2013)
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Figure 13-5: Flow for a year for the River Medway at Chafford (Taken from Centre for Ecology & Hydrology, 2013)
13.2 Systematic Model Analysis
The systematic model of the river was then broken down into sections that assess whether there is a balance is the mass of water within that section of the River Medway. Using the mass balance principles shown in Figure 13-6 and Figure 13-7; each of the sections of the River Medway were analysed.
Q Q 1 3
Q 2
Q = Q + Q 1 2 3 Figure 13-6: First Mass balance principle used
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Q Q 1 3
Q 2
Q + Q = Q 1 2 3 Figure 13-7: Second Mass balance principle used
13.3 Systematic Model Breakdown
Each of the abstractions points as shown in Figure 13-1 were the nodes used in the mass balance analysis; these nodes were Small Bridge, Yalding and Springfield. Section one being the stretch of the River Medway between Bewl and the abstraction point at Small Bridge; Section two Small Bridge to Yalding and finally Section three Yalding to Springfield.
13.3.1 Section 1:
Q 31 River Tesie
Q 21 Small Bridge Abstraction Point
Q 11 Bewl
Water
Q = Q + Q 11 21 31
Summer Peak Flow:
Q11 = 8000 + 86400
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= 94400 m3/d
Summer Minimum Flow:
Q11 = 8000 + 25920
= 33920 m3/d
13.3.2 Section 2:
Q 32 River Medway - Q Lower 42 Yalding Abstraction Point
Q River Beult Q River Medway - 52 22 Upper
Q 12 River Teise
Q32 = (Q12 + Q22) – (Q42 + Q52)
Summer Peak Flow:
Q32 = (86400 + 77760) – (13000 + 17280)
= 133880 m3/d
Summer Minimum Flow:
Q32 = (25920 + 21600) – (13000 + 4320)
= 30200 m3/d
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13.3.3 Section 3:
Q33 Allington
Q23 Springfield
Abstraction Point Q13 River Medway - Lower
Q13 = Q23 + Q33
∴ Q33 = Q13 – Q23
Summer Peak Flow:
Q33 = 691200 – 5220000
= 169200 m3/d
Summer Minimum Flow:
Q33 = 216000 – 5220000
= -306000 m3/d
Therefore the maximum abstraction flow cannot be taken from the river at the minimum flow in the summer months and a smaller amount can be abstracted instead.
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Safety Considerations and Statutory Issues
River weirs are significant engineering structures which regardless of their location of placement have to deal with demanding environmental conditions. Therefore, it is really important that a new weir is designed by a competent design team to qualify structurally, hydraulically and under health and safety requirements. Apart from the need to put together an appropriate weir design, there is a subsequent need to consider the weir’s impact to the environment after its installation and throughout its design life (Rickard, et al., 2003). A feasibility study for a river weir is required to cover the major issues likely to appear due to the operation of the structure, before the application for planning permission. This section will provide a summary of the legal requirements and considerations that need to be taken into account and will further cover the necessary license documents required for the next steps of the study. It has to be kept in mind that planning permission is not likely to be granted by the Environment Agency until all of the licensing issues have been settled.
14.1 Health and Safety Requirements
For ensuring that health and safety practise is managed and co-ordinated at all times throughout the planning, design and construction processes, the ‘Construction (Design and Management) Regulations 2007 (CDM 2007)’ have to be integrated within the project. The CDM Regulations apply to weir structures as much as they apply to any form of structural construction. Through a hierarchy of responsibility that involves all personnel in all of the project’s processes, health and safety practise is to be maintained through identifying hazards early on, reporting to the higher-ups and eliminating or reducing the problem (Health and Safety Commision, 2007).
14.1.1 Recreation The River Medway offers a wide range of opportunities for recreational activities such as boating, canoeing and fishing (Environment Agency, 2013). The installation of a movable weir on the river way could potentially reduce its overall recreational value. For example, a number of reports on cases of people falling, getting trapped or drowning with the reasoning of the lack of safety around weirs can be found. The Water Act 1989 mentions numerous legal requirements regarding the protection of the amenity and recreation in rivers. The design of a weir needs to provide care to all parties using the river and therefore it is necessary to consider all possible uses and risks during the design process (Rickard, et al., 2003). Appropriate design and construction procedures can that way ensure that any risks associated are eliminated or minimised.
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14.1.2 Navigation The navigation rights on the River Medway are controlled by the navigation authorities. The Medway Ports Authority is the navigation authority for the reach of river from Allington to the Medway Estuary which is affected by tidal waters (Environment Agency, 2013). By planning to construct a moveable weir downstream of Allington Lock, it means that it has to be able to integrate the safe passage of vessels within its design as the route of navigation would otherwise be obstructed. Depending on the means chosen to allow for navigation (navigation lock etc.), the requirements are going to be different. In any case, the proposed navigation plans would need to be approved under the Medway Ports Authority Act 1973 and work in accordance with the draught and passage timeline specifications given for Allington Lock (Medway Ports Authority Act, 1973).
14.1.3 Engineering Issues A weir, as a structure, needs to be designed as robust, long lasting and relatively maintenance free since it will mostly operate submerged, under hydraulic pressure. It is very important that the designer team has obtained good knowledge and data of the site and the site’s conditions respectively and consider absolute safety over cost effectiveness. The main sections that need to be investigated carefully are the hydraulics and foundations of the weir (Rickard, et al., 2003).
Regarding the hydraulic design of the weir and the hydro-unit, the data used should be data gathered throughout years, including as accurate worst and best case scenarios as possible in order to be able to produce a design which will be capable to operate effectively under expected future conditions. This will help tackle the variable flow range present in the South-East of England and plan the construction process of the structure. In terms of the consequences of the weir’s hydraulic operation, when the weir is deployed during high tide, it is important to pay attention to flood risk if any.
Regarding the foundation design for a weir, the common causes of stability uncertainty are the hydraulic forces estimated and the potential loss of foundation support. It is not that rare to construct on weak foundations by fault but it is much more often that seepage or erosion downstream leads to the loss of foundation material and support. Therefore, it is highly important to possess accurate data on the site’s soil characteristics (permeability, bearing strength etc.) to wisely choose a foundation design (Rickard, et al., 2003).
Finally, when it comes to weir design, there is a wide selection of materials to pick from and the choice has to be on economic and sustainability grounds. The materials chosen have to be both competent for structural integrity and hydraulic but also for the safety of the ecology and all users. Arriving at the right solution will be in compromise of conflicting requirements (Rickard, et al., 2003).
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14.1.4 Risks in Operation, Maintenance and Construction As the moveable weir is planned to be installed at a low downstream point, close to the top of the Medway Estuary, it is fundamental to provide safe access routes for weir operators and other users. All moveable weirs consist of a mechanism which drives their operation. Also, there is a possibility that a small scale hydro-unit will be incorporated within the weir’s width with flow monitoring equipment and usual maintenance demanding components. Therefore, this scheme will probably require increased maintenance attention in comparison to a stationary weir and it is very important that the means to carry out the maintenance procedures upstream and downstream of the weir are considered in the design process. According to the Environment Agency, in the case of a weir and a hydro-power unit, a license to impound and a license to abstract water are required to be obtained from the organisation itself (Environment Agency, 2014)
The construction process for the installation of a weir is another significant parameter in safety. A construction method for such works needs to be planned accordingly by considering seasonal site conditions in order to ensure that other operations are not obstructed and that an environmental issue is not caused (Rickard, et al., 2003). Under the Land Drainage Act 1991 and the Water Framework Directive 2000, works obstructing a watercourse, relevant to the construction of a weir and further for the hydro-power unit require a planning permission provided by the drainage authority which in this case is the Council of Medway (Land Drainage Act, 1991) (Directive 2000/60/EC, 2000).
14.2 Environmental Issues
When constructing a new weir at a location where it used to involve no flow-to-structure interaction, there are a number of impacts that could be imposed on the environment. This is the reason why the local planning authority, which in this case is the Environment Agency, requires an ‘Environmental Statement’ for every new structural project planned for placement on the river course. When undertaking an environmental assessment it is very important to consider the legislation applying and both short-term and long-term potential environmental impacts.
14.2.1 Landscape Amenity Under section 16 of the Water Resources Act 1991, the Environment Agency has to protect naturally conserved sites against proposals that may harm their current amenity (Water Resources Act, 1991). The planning process for the construction of a new weir has to respect the visual characteristics of the river course and work to enhance or retain them. Therefore, the scale and the plan of a weir have to be thoroughly studied. The weir has to fit effectively with the river bed’s cross-section without overly
STAVROS KYLKOS SAFETY CONSIDERATIONS AND STATUTORY ISSUES PAGE | 40 TIDAL WATER RESOURCES | TEAM MEDWAY destroying the natural course and could also be constructed in a shape to fit the natural characteristics of the river instead of an extended rectangular right angle block (Rickard, et al., 2003).
14.2.2 Aquatic & Fish Protection & Water Quality A stationary weir would usually more or less affect the sensitive forms of habitat upstream of the weir as the water level rises and the volume increases in the resulting reservoir. When it comes to a movable weir, depending on the frequency of deployment, the level at which the surrounding wildlife and flora is affected should be investigated. Under the Council Directive of the Conservation of Natural Habitats and of Wild Fauna and Flora it is required to undertake that environmental assessment for all of the identified and listed protected species present (Directive 92/43/EEC, 1992).
As previously mentioned, a new weir will create an obstruction and it is important that appropriate provisions are made for the passage of fish. This is because all fish species have the need to migrate for one reason or another and a weir and a hydro-unit can be an obstacle to that. Under several regulations such as the Salmon and Freshwater Fisheries Act 1975 and the Eels Regulations 2009 No.3344 fish passes and screening is required for the migration and protection of the respective species (Salmon and Freshwater Fisheries Act, 1975) (Eels Regulations, 2009). Therefore, there is a need to investigate that.
It can be confidently stated that when the weir is fully deployed, water quality will be improved through aeration as water crushes onto the walls (Rickard, et al., 2003). However, as the weir is not going to be deployed extensively throughout the whole year, and the degree of aeration is not going to be certain, the additions of dissolved oxygen to the water have to be investigated in order to identify how the aquatic environment could be affected. In addition, as a pool reservoir will be formed every time the movable weir is deployed and in position to impound tidal water, it is very important to investigate the increase of salinity in the water for the same reason as stated above. As the site is going to be involved with tidal water, under the Marine and Coastal Access Act 2009 and in accordance with the Wildlife and Countryside Act 1981 (amended 2000), a structure likely to affect the surrounding wildlife on a UK marine licensing area requires consent from the organisation (Marine and Coastal Access Act, 2009) (Wildlife and Countryside Act, 1981).
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Design Procedure for Movable Weirs 15.1 Site Parameters
Clay Soil 60m Wide River
15.2 Required information
Cross sections of river- unknown at this stage but assumed as worst case in this report as detailed in section 11 Water levels and tidal variations: 0.08m-3.58m Wind Speeds: not applicable as the weir is submerged
15.3 Applied Forces
15.3.1 Environmental Forces: 15.3.2 Ship Collisions Hydrostatic Low Probability but high consequence Current Forces Foundation Design Wind Loads
Operating Forces Temperature Icing: (salt water so unlikely)
15.4 Navigation Requirements
The extended length of the reach means that the river level when the weir is in operation is not high enough for boats to pass anyway, therefore a lock in not required.
15.5 Operational Requirements
Debris Protection Navigation Safety: Signs require to warn boats about the approaching weir Sedimentation
These factors have led to the decision that rotating radial gate would be the best configuration for the scheme. This is because the curved face and long radial arms make it easier to lift than a flat gate, so
JESSICA HYLAND DESIGN PROCEDURE FOR MOVABLE WEIRS PAGE | 42 TIDAL WATER RESOURCES | TEAM MEDWAY less energy is needed to operate it. It has also been decided to operate the weir by using a system of floats and buoyancy aids to further reduce the amount of energy required to use it, using this system there will be no external power supply to the gate.
Figure 15-1 Schematic of weir
Figure 15-1 shows a cross section of the weir with counter weight and radial gate face. In order for the weir not to be affected by bow waves, which may cause torsion about the central hinge, the floats are only at each end, are inside a concrete housing which offers some protection from the waves and are mounted on springs so that only significant changes in water level will cause the weir to move.
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Design of Weir 16.1 Operation of Weir
The weir has been designed as a rotating radial gate which moves due to the buoyancy of counterweights affixed to each end. See Drawings 1 and 2 for more detail.
16.2 Hydrostatic Forces
The line of action of the water thrust on radial gates passes through the centre of curvature of the skin plate. For ease of calculation the resultant water thrust is determined from its horizontal and vertical components.
Table 16-1 Calculations for Hydrostatic Forces (All equations from (Erbisti, 2014))
Ref Calculation Result 4.15 Horizontal component of water thrust ℎ 푊 = 훾퐵ℎ (퐻 − ) ℎ 2 4.16 Vertical component of water thrust Wv R(α -α ) R(sin α cos α - sin α cos α ) = 훾퐵푅 [D (cos α - cos α )+ i s + s s i i ] m s i 2 2 where γ = specific weight of water = 9.81 kN/m3 B = side seal span = 60m R = skin plate radius (measured on the wet surface) = 1.6m H = maximum headwater on sill = 1.4m h = gate sealing height = 1.4m Dm = difference between the elevations of the water level and the centre = 1.4m of curvature of the skin plate 4.17 αs = arc sin Ds/R = 1.06rad 4.18 αi = arc sin Di/R = 0= 0rad Ds = difference between the elevations of the centre of curvature of the skin plate and the top seal = 1.4m Di = difference between the elevations of the centre of curvature of the skin plate and the sill. = 0m
4.15 Horizontal component of water thrust 10.1 × 60 × 1.0(1.4 − 0.7) = 593kN 4.16 Vertical component of water thrust 10.1×60 ×1.6 [1.4×(cos 1 - = -441kN 1.6(0-1) 1.6(sin 1 cos 1 - sin 0 cos 0) (downward) cos 0 )+ + ] 2 2
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Ref Calculation Result 4.19 Resultant force
2 2 =738kN 푊 = √푊ℎ + 푊푣 4.20 Angle of force 훽 = arctan 푊푣/푊ℎ = -36
16.3 Structural Design
Figure 16-1 Structural members of the radial gate (Erbisti, 2014)
16.3.1 Skin Plate The skin plate of segment gates is made up of curved plates joined by butt welds. The minimum recommended thickness is 8 mm, except for small weir gates, where 6.5 mm plates may be used. For ease of manufacture and transportation, the skin plate is usually subdivided into horizontal elements. The arc length of the various elements should be the greatest possible (but within the transportation limits) to reduce the amount of field joints, for this scheme it is more than likely possible that the weir can be transported in sections of complete height and 6m widths, this corresponds with the span to each section between the radial arms. Butt welding of the skin plate and vertical girder carries out the union of the elements on site.
As there is a facility to inspect and maintain the weir in situ, there is no need to provide additional thickness of the skin plate for corrosion.
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16.3.2 Gate Framing 16.3.2.1 Girder Arrangement The skin plate is strengthened with an arrangement of horizontal and vertical girders.
Figure 16-2 Rear view of radial gate showing girder arrangement
Figure 16-3 Typical Arrangements of girders
For the design shown in Figure 16-3 Typical Arrangements of girders, the gate framing comprises a series of auxiliary vertical beams, made of curved rolled sections, supported on the main horizontal girders.
16.3.2.2 Horizontal Beams The horizontal beams are supported on the radial arms.
The maximum moment in the span of the horizontal girders is 15kNm therefore a 152x89x16UKB has been selected as the beam size.
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16.3.2.3 Vertical Beams For this weir the arms will be equally loaded in the axial direction – this occurs when the direction of the maximum water thrust matches the bisector of the angle between the upper and lower arms.
Table 16-2 Vertical Girder Calculations Equations from (Erbisti, 2014)
Ref Calculation Result
Figure 16-4 Segment gate with 2 pairs of arms showing geometry
For gates with two pairs of arms: (5.23푎) 푙1 = 0.1414 퐿 0.2m (5.23푏) 푙2 = 0.4734 퐿 0.69m (5.23푐) 푙3 = 0.3852 퐿 0.56m
Vertical Beams to be dimensioned as straight ones with a triangular load. The horizontal girders provide the support.
Figure 16-5 Loading on the vertical beams
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Ref Calculation Result Bending moments at the supports per unit width are: 훾푙2 푀′ = 1 (2ℎ + ℎ ) (5.25) 퐴 6 𝑖 푎 0.22 푀′ = 10.1 × (2 × 1.4 + 1.202) 퐴 6 =0.27kNm/ 2 m 푙3 (5.26) 푀′ = 훾 ℎ =1.566kNm 퐷 6 퐷 2 ′ 0.56 푀퐷 = 10.1 × × 0.56 =0.28kNm/ 6 m =1.624kNm Bending moment at the mid span is:
′ ′ 푥ℎ퐷 (ℎ퐴 − ℎ퐷)푥 푀퐴 + 푀퐷 (5.27) 푀′ = 훾 [ (푥 − 푙 ) + (푥2 − 푙2)] + 퐵 2 2 6푙 2 2 2 0.345×0.56 (1.202-0.56)×0.345 ' 2 =-0.254kNm/m MB=10.1 [ (0.345-0.69)+ (0.345 - 2 6×0.69 =-1.47kNm 0.27+0.28 0.692)] + 2
Length between restraints is 0.69m Use section: 76x76x13RSJ (bending radius 0.8m ideal for this situation)
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16.3.3 Radial Arms Table 16-3 Calculations for Radial Arms (All equations from (Erbisti, 2014))
Ref Calculation Result The radial arms transfer the water thrust acting on the leaf to the bearings.
Axial load on each upper arm: (5.29) 푊 sin 훾𝑖 푅푠 = 2 sin(훾𝑖 + 훾푠) Axial load on each upper arm: (5.30) 푊 sin 훾푠 푅𝑖 = 2 sin(훾𝑖 + 훾푠) Where: =693kN W= Water thrust =18 훾𝑖= Angle from centroid to lower arm =10 훾푠= Angle from centroid to upper arm
693.6 sin 18 =228.12kN 푅 = × 푠 2 sin 28
693.6 sin 10 =128.2kN 푅 = × 𝑖 2 sin 28 Use 76x76x13RSJ
16.4 Mechanics of Weir
The weir is designed to rotate about a central bearing as the tide comes in and out. In order for this to happen a floating counterweight is fixed to the opposite arm to the weir.
Table 16-4 Calculations for counterweight Design (All equations from (Erbisti, 2014))
Ref Calculation Result The counter weight needs to have a buoyancy equal to the weight of the weir in order for it to offset the weight of the weir, it also need to have the same weight. Forces to be considered for the movement of the gate. G = gate weight E = buoyancy of the submerged part Fa = friction forces on supports Fv = friction forces on seals
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Ref Calculation Result Gate Weight:
Gate Face: 60푚 × 0.006푚 × 1.96푚 × 7850푘푔/푚3 =5538kg Radial Arms: 2 × 11 × 1.6푚 × 13푘푔/푚 =457kg Vertical Beams:11 × 1.96푚 × 13푘푔/푚3 =280.3kg Horizontal Beams: 4 × 60푚 × 13푘푔/푚 =3120kg
In order to allow for the weight of paints and debris a factor of 1.05 is used =9865kg =96.8kN Moment about the hinge due to gate weight: 푀푝 = 96.8푘푁 × 1.6푚 =154.88kNm Buoyancy of submerged parts: =-7.13kN 3 3 퐹푏 = 훾푤푉 = 10.1푘푁/푚 × 0.706푚
Moment about the hinge due to buoyancy =-11.408kNm 푀푏 = −7.13푘푁 × 1.6푚 Friction Forces on Supports =15.606kNm 푑 0.3푚 푀 = 휇퐹 = 0.15 × 693.6푘푁 × 푚 푟 2 2
Total Moment to overcome: =181.984kNm 푀푟 = 푀푝 + 푀푏 + 푀푚 = 154.88 + 11.408 + 15.606
The radius between the hinge and the counterweight is 2.5m therefore the force exerted by the counterweight will be: 푀 182 =72.8kN 퐹 = 푟 = 푟 푅 2.5
퐹푏 = 훾푤푉 퐹푏 = 퐹푔 퐹푔 = 72.8푘푁 There are two counterweights, one at either end of the bearing beam, thus each only needs to weigh 36.4kN 퐹푏 36.4 푉 = = =3.6m3 훾푤 10.1 If using concrete with a polystyrene void 푚 36.4 푉푐표푛푐 = = 3 휌푐 24 =1.51m (Assuming the polystyrene void has negligible density)
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Ref Calculation Result If the counterweight is capsule shaped with equal radius and cylinder length then: 7 푉 = 휋푟3 3 3 3 × 3.6 푟 = √ = 0.79푚 7휋 Concrete volume =1.51m3 Volume of hemisphere =1.03m3 there for the cylinder section needs to be filled to 240mm
Figure 16-6 Schematic of Floating counter weight showing the concrete filled base
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Column Calculations 17.1 Purpose
The purpose of this is to design the columns for the weir.
17.2 Weir Design
Figure 17-1: Plan View of Weir (m)
Figure 17-2: Side View of Weir Counterweight and Column (m)
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Figure 17-3: Column Labelling
17.3 Forces Calculations
Ref Calculation Result The forces exerted on the columns of the weir are as follows:
Weight of the gate: 400KN
Weight of the counterweights: 400KN (therefore each counterweight 200KN)
Weight of trunion and supports: 500KN
Water loading vertical: -359.81KN
Water loading horizontal: 593KN
Therefore the forces exerted on each the column is as follows:
Columns 1&7:
400 500 359.81 Vertical= ( × 5푚) + 200퐾푁 + ( × 5푚) + ( × 5푚) = 304.95퐾푁 60 60 60
593 Horizontal = ( × 5푚) = 49.42퐾푁 60
Columns 2 – 6:
400 500 359.81 Vertical = ( × 10푚) + ( × 10푚) + ( × 10푚) = 209.97퐾푁 60 60 60
593 Horizontal = ( × 10푚) = 98.83퐾푁 60
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17.4 Cover Requirements
Ref Calculation Result The exposure class shall be assumed to be XS3 (tidal, splash and spray zones) as this is the worst case for the possible scenarios that the concrete columns will be exposed to.
The structural class S4 will be assumed to be required therefore using Table 4.4N from BS EN 1992-1-1:2004 which can be seen in Table 17-1 below.
Therefore the cover required is = 45푚푚
Table 17-1: Cover Requirements (BS EN 1992-1-1:2004, 2004)
17.5 Reinforcement Calculations
To design for the worst load case only columns 1 and 7 reinforcement will be calculated.
The minimum 퐹푐푢 required for the concrete with a XS3 exposure class is C45/55 as per Table 17-2 below.
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Table 17-2: Recommended Structural Classification (BS EN 1992-1-1:2004, 2004)
Therefore initially assume a column of size 250mm x 250mm
Ref Calculation Result Initially assume the use of 20mm steel reinforcement with strength
2 (푓푦푘) 500N/mm
20 = 14푚푚 푑 = + 4 2 2
푑 14 Therefore 2 = = 0.056 ℎ 250
Area of main reinforcement in column:
푁 (304.95 × 103) = 0.11 = 푏ℎ푓푐푘 (250 × 250 × 45)
푀 (49.42 × 1.5) × 106 = 0.105 2 = 2 푏ℎ 푓푐푘 (250 × 250 × 45)
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Figure 17-4: Column design chart (Moss & Brooker, 2006)
Ref Calculation Result Therefore from figure 4 above:
(Moss & 퐴푠푓푦푘 =0.16 Brooker, 푏ℎ푓푐푘 2006)
Therefore area of steel (퐴푠):
0.16 × 푏ℎ푓푐푘 퐴푠 = 푓푦푘
0.16 × 250 × 250 × 45 = 900푚푚2 퐴 = 푠 500
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Ref Calculation Result Therefore use 4 × 20mm diameter bars (1257mm2)
Minimum diameter required is 12mm therefore OK
CHECK - Maximum and minimum areas of reinforcement
9.5.2(2) 푁푒푑 Greatest value of the following: 퐴푠,푚𝑖푛 = 0.1 or 0.002Ac (NA to BS 푓푦푑 EN 1992- 1-1:2004, 2004)
304.95 × 103 = 70.1푚푚2 퐴 = 0.1 푠,푚𝑖푛 500/1.15
2 2 퐴푠,푚𝑖푛 = 0.002 × 250 = 125푚푚
1257mm2 >125mm2 Therefore OK
9.5.2 (3) 퐴푠,푚푎푥 = 0.04퐴푐 (NA to BS EN 1992- 1-1:2004, 2004) 2 2 퐴푠,푚푎푥 = 0.04 × 250 = 2500푚푚
125푚푚2 < 1257푚푚2 < 2500푚푚2 Therefore OK
Therefore initial bar assumption of 20mm is OK
Spacing
푆푝푎푐𝑖푛푔 표푓 푚푎𝑖푛 푏푎푟푠 = 푐표푙푢푚푛 푤𝑖푑푡ℎ − (2 × 푐표푣푒푟) − 푑𝑖푎푚푒푡푒푟 표푓 푏푎푟푠
푆 = 250 − (2 × 45) − (20 × 2) = 120푚푚
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17.6 Transverse Reinforcement
Ref Calculation Result Minimum diameter of reinforcement is the greatest of the following:
6mm bars or 0.25 diameter of main bars
0.25 × 푑𝑖푎푚푒푡푒푟 표푓 푚푎𝑖푛 푏푎푟푠 (20푚푚) = 0.25 × 20 = 5푚푚
Therefore transverse reinforcement 6mm diameter
Spacing:
9.5.3 (3) Spacing of the transverse reinforcement must not exceed the following: (NA to BS EN 20 times the minimum diameter of the longitudinal bars 1992-1- 1:2004, The lesser dimension of the column 2004) 400mm
20 × diameter of longitudinal reinforcement = 20 × 20 = 400푚푚
Lesser column dimension = 250푚푚
400mm
Therefore 250mm spacing required.
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Figure 17-5: Column Cross Section (mm)
Figure 17-6: Column Longitudinal Cross Section (mm)
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Foundation Bearing Capacity
18.1 Purpose
The purpose of this is to calculate the bearing capacity of the soil for the foundations of the weir.
18.2 Local Soil Conditions
Table 18-1: Borehole Data (all data obtained from British Geological Survey (British Geological Survey , 2014))
Borehole TQ75NW43 Borehole TQ75NW240
Depth (m) Material Depth (m) Material
0-0.3 Topsoil 0-5 Alluvium: stiff greenish blue clay
0.3-2.3 Loam 5-10 Sandy sub angular cherl gravel with sandstone and mudstone fragments
2.3-5 Sandy Loam 10-25 Folkestone bens: Medium grained sub rounded well sorted glauconitic yellow/green sands
5-6.6 Ballast 25-? Sandgate Beds: Sandy blue/green/grey clay
6.6-7.3 Kent Ragstone ?-50m Hythe Beds: Indistinguishable from overlying Sandgate beds
7.3-7.6 Ballast
7.6-14 Grey rock and clay layers
14-29 Sandy blue clay
29-35 Loamy Sand and pyrites
35-39.3 Blue clay
39.3-41.6 Weald clay
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Figure 18-1 Borehole locations (British Geological Survey , 2014)
18.3 Bearing Capacity Calculations
The Foundation Footing will initially be assumed to be 6m by 60m as per Figure 18-2 and the edges will be constructed to a depth of 3.6m. The centre will be actually at ground level but due to the fact that the river has eroded material away the equivalent depth when compared to that of the borehole will remain the same across the weir.
Figure 18-2: Weir Dimensions
As can be seen from the Borehole data in Table 18-1: Borehole Data (all data obtained from British Geological Survey )Table 18-1 constructing at 3.6m means that construction will likely be occurring in
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Sandy Loam or Alluvium: stiff greenish blue clay. Due to the less disturbed nature of the soil in TQ75NW240 (no ballast) it will be assumed that the material to be constructed on is the Alluvium: stiff greenish blue clay.
It will have to be assumed that the following data applies to this material due to the fact there is no data provided in the borehole survey. C’=0, ϕ’=24 unit weight 20kN/m3 (Cobb, 2011)
Using Table 18-2 below the bearing capacity factors can be obtained
Table 18-2 Drained bearing capacity factors (Woods & Matthews, 2013)
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Ref Calculation Result (all equations taken from Eurocode 7 (British Standards Institute, 2004)) ′ 푐 = 0 ϕ’ = 24 ∴ 푁푞 = 9.60, 푁훾 = 6.89 푁푐 = 6
퐷 3.6 퐵 6 = = 0.6 = = 0.1 퐵 6 퐿 60
The foundation is pad shaped, therefore
푆푞 = 1.00 푆훾 = 1.00
2 2 푑푞 = 1 + 2푡푎푛ϕ’(1 − sinϕ’) 퐷/퐵 = 1 + 2푡푎푛24 × (1 − 푠𝑖푛24) × 0.6 = 1.18
푑훾 = 1.0
Load inclenation factors:
593×1.5 퐼 = (1 − ) = 1 푞 1659.81+6×60×0×푐표푡24
ퟏ−ퟏ 푰 = ퟏ − ( ) = 1 휸 ퟔ풕풂풏ퟐퟒ Assume ground water level well below base of foundation (same as ground water level at base as the submerged unit weight of the soil is unknown
′ 푃표 = 푃 표 = 훾퐷 = 20 × 3.6 = 72
1 푞 = 푃′ (푁 − 1)퐼 + 퐵훾푁 퐼 + 푃 푓 표 푞 푞 2 훾 훾 표
= 72(9.6 − 1)1 + (0.5 × 6 × 6.89 × 1) + 72 = 711.87 퐾푁/푚2 Assume ground water level rises to surface
푃표 = 훾퐷 = 20 × 3.6 = 72
푃′표 = (20 − 10) × 3.6 = 36
푞푓 = 36(9.6 − 1)1 + (0.5 × 6 × 6.89 × 1) + 72 = 402.27 퐾푁/푚2 Safe bearing capacity is therefore:
When ground water level at the surface
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Ref Calculation Result (all equations taken from Eurocode 7 (British Standards Institute, 2004))
402.27−72 = 182.09 푞푠 = + 72 3 퐾푁⁄푚2
18.4 Gross Applied Load
Greatest load exerted on columns from dead weight of gate, counterweight, trunnion and support and live loading from water = 304.95kN
Weight of the columns: [(1.5 × 0.25 × 0.25) × 24] = 2.25퐾푁
Weight of pad foundations(1.4 × 1.4 × 0.25) × 24 = 11.76퐾푁
Therefore Total loading from pad foundations = 304.95 + 2.25 + 11.76 = 318.96푘푁
318.96 = 162.7 푘푁⁄푚2 < 182.09 Therefore no piles required 1.42
18.5 Foundation Settlement
The pad foundation is 1.4m × 1.4m and is founded at 3.6m the soil profile can be seen in Table 18-3 below:
Table 18-3: Borehole Data (British Geological Survey , 2014)
Depth (m) Material 0-5 Alluvium: stiff greenish blue clay 5-10 Sandy sub angular cherl gravel with sandstone and mudstone fragments 10-25 Folkestone bens: Medium grained sub rounded well sorted glauconitic yellow/green sands 25-? Sandgate Beds: Sandy blue/green/grey clay ?-50m Hythe Beds: Indistinguishable from overlying Sandgate beds
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Ref Calculation (all equations taken from (Skempton & Bjerrum, 1957)) Result
Figure 18-3: Soil Profile
Figure 18-4: Pad Foundation Plan View
Assume all layers have the following values of mv=0.35 and A=0.35
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Ref Calculation (all equations taken from (Skempton & Bjerrum, 1957)) Result
Figure 18-5: Influence coefficients for the increase of vertical stress at points beneath the corner of a uniformly loaded flexible rectangular area (Fadum, 1948)
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ퟐ Z(m) m n 푰흈 (obtained ∆흈′풗(풌푵⁄풎 ) 푷풐풆풅(풎풎) Layer from Figure 18-5) 1 0.7 1.00 1.00 0.176 4 × (162 × 0.176) = = 푚푣 × ∆휎′푣 114.05 × ∆퐻 = 0.35 × 114.05 × 1.4 = 55.9 2 3.9 0.18 0.18 0.015 9.72 17.01 3 13.9 0.05 0.05 0.003 1.94 10.19 4 33.9 0.02 0.02 0.001 0.65 5.69 SUM: 88.79mm
Ref Calculation Result
Square foundation, therefore need to find size of the equivalent circle
휋퐵2 = 1.4 × 1.4 ∴ 퐵 = 1.58푚 4 퐻 1.4 = = 0.89 퐵 1.58
Figure 18-6: Values of Skempton - Bjerrum settlement correction factor 흁 (Skempton & Bjerrum, 1957)
Therefore 휇 = 0.6
푝푐 = 휇 × 푝표푒푑
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푝푐 = 0.6 × 88.79 = 55푚푚
Therefore consolidated settlement = 55mm
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Slab Design 19.1 Design Purpose
The purpose of this is to design the foundation raft slab of the weir.
19.2 Foundations Dimension
Figure 19-1: Foundation Cross Section (m)
For the purpose of this design it will be assumed that the slab of width x in Figure will be designed and it will be assumed that the shaded area will simply require minimum reinforcement to allow for ease of design. This slab will be treated as a pad foundation supporting each column.
Figure 19-2: Plan View of Weir (m)
All equations taken from Eurocode 2 BS EN 1992-1-1:2004 (British Standard, 2004)
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Ref Calculation Result
The vertical loads acting on the pad foundation are:
column 1&7 vertical load from column calculations – forces calculations section + weight of column 304.95KN + (1.5 × 0.25 × 0.25 × 24) = 307.2퐾푁
Therefore the pad foundation base size must be a minimum of
퐼푚푝표푠푒푑 푙표푎푑 307.2 2 = = 1.69푚 푠푎푓푒 푏푒푎푟𝑖푛푔 푝푟푒푠푠푢푟푒 182.0
Therefore pad dimensions = √1.69 = 1.3푚2
Base thickness shall be assumed to = 250mm
Therefore pad foundation dimensions are:
1.4푚 × 1.4푚 × 0.25푚
As foundations are in the same conditions as the columns the following values are to be used:
XS3 exposure class and structural class S4 therefore cover 45mm
C45/55 concrete
Loading: 1.5 × 307.2 = 460.8푘푁
ULS bearing pressure= 460.8/1.42 = 235.1푘푁/ 푚2
Critical section at face of column:
1.4 − 0.25 2 = 54.4푘푁푚 ( ) 푀 = 235.1 × 1.4 × 2 퐸퐷 2
Effective depth of base= Pad thickness – (2 × cover) –bar diameter (assumed to be 20mm)
푑 = 250 − (45 × 2) − 20 = 140푚푚
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Ref Calculation Result
54.4×106 퐾 = = 0.044 1400×1402×45
푧 = 0.95 × 푑 = 0.95 × 140 = 133푚푚
퐴 = 푀 푠 퐸퐷/(푓푦푑×푧)
54.4×106 = 940.8푚푚2 = 500 ×133 1.15
Therefore use 4 × 20mm reinforcing steel (1257mm2)
19.2.1 Beam shear check
Check critical section distance d away from the column face
푉퐸푑 = 235.1 × (0.575 − 0.140) = 102푘푁/푚
102 푉 = = 0.73푀푃푎 퐸푑 140
Table 19-1: VRd,c resistance of members without shear reinforcement, MPa (Brooker, 2005)
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Ref Calculation Result
휌1 = 퐴푠/(푏푑)
푏 = 250 + 2푑 = 250 + (2 × 140) = 530mm
휌1 = (940.8/(530 × 140)) × 100 = 1.27%
Multiply answer by fck factor 1.14
1.27 × 1.14 = 1.45%
푉푅푑,푐(푓푟표푚 𝑖푛푡푒푟푝표푙푎푡𝑖표푛 표푓 Table 19-1) = 0.77 > 0.73 Therefore OK
19.2.2 Punching shear check
Check the basic control perimeter at 2d from face of column
퐵푉퐸푑 푉퐸푑 = < 푉푅푑,푐 푢푖푑 Where B=1 푢𝑖 = (250 × 4 + 140 × 2 × 2 × 휋) = 2759푚푚
푉퐸푑 = load minus net upward force within the area of the control perimeter
= 307.2 − 272.7 × (0.252 + 휋 × 0.282 + 0.28 × 0.25 × 4) = 146.6푘푁
1×146.6×103 푉 = = 0.38 퐸푑 2759×140
푉푅푑,푐 = 0.77 >0.38 Therefore OK
Therefore the use of a 1.4m × 1.4m × 0.25m pad underneath each column will be OK
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River Modelling
20.1 Aims and Objectives
As part of the project it was necessary to construct a model to determine how well the proposed design of the moveable weir operates. There were three main requirements of the brief that the model aims to address, which are listed below:
To calculate the operation of the weir that allows the flow into the Medway estuary to be above the minimum residual flow for as long as possible. To evaluate how much water can be abstracted from the river when the moveable weir is in operation. To determine to what extend the operation of the weir is affected by environmental changes (such as river flow and sea level)
In order to do this the hydraulic river modelling program “ISIS” was used to create a 1D model of a portion of the Medway large enough to include any significant factors that might affect the operation of the tidal reservoir. Once the required model parameters were assessed, as much of the data required to generate the model that could be retrieved was collected and where it was not possible to obtain precise data, informed approximations were made. Following on from this the model was then assessed for accuracy against recorded and gauged data in order to ensure it provided an adequate approximation of the river system.
Having constructed the model, the focus of the project was to determine how much water could be abstracted from the river using the scheme during lower flow conditions. The first objective was to find the optimal characteristics for operation of the proposed weir design to allow the largest volume of water to be abstracted from the river. The next aim was to determine how invariable the weirs operation is to changes in river conditions. The two scenarios tested were past worst case river flows (as seen in the 1976 drought) and predictions of future flows for both typical and drought conditions. The results generated will help to show how effective the operation of the weir will be in terms of rates of abstraction through its lifetime. In the short term the weir may be able to significantly reduce the amount of water that is required to be released from Bewl water reservoir. However, the nature of the weir’s operation means that the abstraction rates are still dependant on changes of flows in the river. In a predicted future worst case droughts, although the weir will still able to make a significant contribution to the overall water resources available, it is not enough to make Bewl water redundant if adequate river levels are to be maintained to provide enough water for abstraction.
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20.2 Scope of the Model
Figure 20-1 Key points in the model shown in the geographical setting (a) and their 1 5 2 contribution to the modelled system (b) 6 The boundary conditions chosen for the model are shown in Figure 20-1. The Flow at Teston was
chosen as the primary input for the model. Teston is one of the oldest gauging stations along this stretch of the river with gauged data going back to 1956. Consequently, it provides a wide range of river flow conditions to use as input for the model including severe droughts such as that in 1976. The flow at this point of the river was also the subject of a study undertaken on future river flows in the Medway (Cloke, et al., 2010) so the predictions made in their report would be directly applicable to the river flow data being used for the Medway. The river flow data was retrieved from the National River Flow Archives, a service run by the Centre for Ecology and Hydrology (Centre for Ecology and Hydrology, 2014).
In addition there were two further inlets to the Medway in the section modelled, the Loose Stream and the River Len. The River Len was the larger of the two rivers, and was included in the Medway Catchment Abstraction Management Strategy (CAMS) (Environment Agency, 2013, p. 19) and was therefore considered a significant input to creating an accurate model. However, as the Loose Stream was not included in the CAMS report and was ungauged it was assumed this inlet had little effect on overall river flow in the Medway. The gauging station for the River Len as shown in Figure 20-1a (point 3) is located at Lenside, and complete river flow data was available back to 2002 onwards and for several years in the 1990s, with partial data available back to 1984. Again, this river flow data was retrieved from the National River Flow Archives.
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It was not possible to obtain gauged data for river levels at the downstream boundary of the model but mean neap and spring tides were obtained for several locations in the tidal section of the Medway (Environment Agency, 2010, p. 93). These values were recorded in meters above datum (mAD) (equivalent to meters above the average sea level) based on the 2006 Admiralty Charts. The closest location for which data was available downstream of the moveable weir was at New Hythe. Records of sea levels at the mouth of the Medway estuary, at Sheerness were available online (British Oceanographic Data Center, 2014) and were used to estimate the frequency of tides and the time between neap and spring tide. From this data it was apparent that a period of 12 hours would provide an adequate approximation of a single tidal period. The distance between neap and spring tides present in the data was found to be approximately 29 tide periods. Using this data an amplitude-modulated sine wave was used to model the river levels at New Hythe, as shown in Figure 20-2.
4
3
2
1
0 River Level (mAD) 0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 -1
Time (hours) Figure 20-2 Modelled Tidal Levels at New Hythe with a neap high tide of 2.38, a spring high tide of 3.58 and a constant low tide at -0.35
As it was not possible to obtain cross sections of the river channel it was necessary to make approximations. In line with the initial worst case scenario used in calculating the river water storage capacity for the proposed estuary reservoir, a ‘V’ Shaped river cross section (as shown in Figure 20-5a) was used as a starting point for the model. In order to calculate the width of the river at certain key points, the distance between the river banks were measured using aerial photographs obtained from Bing maps. As shown in Figure 20-3 more cross section widths were found for the downstream extent of the river as the accuracy of this section in the river was more critical to evaluating the operation of the estuary reservoir. Data from the navigation chart of the Medway (Environment Agency, 2013) was used to find the heights of the weirs. Furthermore, as better data couldn’t be obtained, the gradient of the river bed was calculated using the differences in heights of the three weirs (Teston, East Fairleigh and Allington) and the distance between them. As there was a suggested decrease in river gradient in
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the navigation charts, the gradient after Allington was assumed to be half the previous gradient (between Allington and East Fairleigh). A diagram of the overall river gradients is shown in Figure 20-3. The overall model schematic is shown in Figure 20-4.
Figure 20-3 Long Section of the River Modelled with drops in river level occur at the two weirs, East Farleigh and Allington.
Medway at Teston East Fairleigh Weir Len Inlet at Lenside Abstraction Point Allington Weir
Movable Weir Downstream Boundary at East Hythe
Figure 20-4: Schematic of the river model. Dots between object represent river sections
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20.3 Construction and Calibration of the Model
In order to test the model created two sources of data were obtained. The first of these was the flow rates at Allington weir, obtained from the Environment Agency (EA). The second was annual exceedance probabilities at various points in the river for which the EA held data, from just before Teston Weir to Allington Weir. In order to check the validity of the model the flow rates both for wet and dry periods were tested in order to ensure the model was valid at the opposite ends of flow rates. The validity of the model could then be assessed by calculating the average error against the gauged data. River levels for the wet seasons would also be assessed to check the model didn’t produce unrealistically high river levels.
To analyse dry season flow, the drought of 2012 was chosen as it was both a significant and recent drought (Harrabin, 2013) for which complete flow data would be available at Teston, Lenside and Allington. The dates used for the model were between the 10th March and the 17th of April where for all but one day the average daily flow at Teston fell below 2m3/s. For higher flow conditions the winter of 2010 was used to assess the model for winter flow in the Medway. A period of extreme wet weather (likely to cause floods) was not used to test the model as it wasn’t calibrated to simulate the river spilling over its banks. In periods of flood and high flow the proposed movable weir would not be in operation, and therefore would not be likely to have much of an effect on river flow.
20.3.1 River Levels As average exceedance probabilities (AEP) for the Medway were only available between Teston and Allington the assessment of river levels was restricted to this area. The first points in the river chosen were at Teston and Allington to cover the full extent of the river for which data was available. In addition, two intermediate points at Tovil (between the East Fairleigh Weir and the Len inlet) and at Maidstone just after the Len inlet (see Figure 20-1a).
When assessing the river levels it was found that with the initial model conditions the water levels were significantly higher than the annual exceedance probability (as shown in Table 20-1). One possibility was that as the V-shaped cross section (Figure 20-5a) had low volume per unit depth and as a consequence was causing higher river levels. In contrast, a U-shaped cross section (Figure 20-5b), with a greater river capacity might provide lower and more accurate river depths. In order to test the effect this had on the river levels the model was run for the two cross sections types (as shown in Figure 20-6) for the period 1st September 2009 to 1st June 2010 to compare the resulting river levels. A U-shaped river channel cross section would have sharp 3m wide banks on each side descending to 1m above the
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predicted maximum depth. The river would then have a gentle sloped V-shaped base, descending the final 1m to the rivers maximum depth at the centre of the channel.
a) b) Figure 20-5 The V-(a) and U-(b) shaped river profiles tested
From the results shown in Figure 20-6 it was found that using a U-shaped cross section did have the effect of lowering the higher river level values downstream of Teston. As a consequence, for the U- shaped channel the maximum head at Teston was reduced to levels below the annual exceeded flow. However whilst being somewhat reduced, river levels after East Fairleigh still exceeded the AEP. Comparing the river levels in Figure 20-6 with AEP levels shown in Table 20-1, levels at Tovil are over 10% AEP, at Maidstone exceed 2% AEP and water levels at Allington are constantly higher than 1% AEP.
Figure 20-6 River levels along the Medway depths for U-shaped and V-shaped river channel
Table 20-1 Modelled Cross Sectional Flood Levels for Annual Exceedance Probability shown in mAoD (Data is obtained from the Environment Agency)
Modelled Cross Sectional Flood Levels for Annual Exceedance Probability shown in mAoD
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Location 50% AEP 20% AEP 10% AEP 4% AEP 2% AEP 1% AEP Teston 9.247 9.353 9.644 10.078 10.575 11.220 Tovil 6.002 6.109 6.407 6.789 7.126 7.505 Maidstone 5.637 5.741 6.021 6.384 6.697 7.081 Allington 4.130 4.130 4.130 4.130 4.130 4.130
Being confined by weirs, the water levels in the modelled river section are heavily dependent on the height and operation of the next weir downstream, and the way water flows through them. From further research it was found that Allington weir was not a conventional weir but actually a sluice gate (New Sluice Gates Opened At Allington Locks, 1937). This means that the head produced by the model at Allington will be higher than in reality, as in the model water passes over the weir, not under it producing higher heads in the river. As there was not sufficient time to retrieve details of the sluice gates operation the sluice gate, it was decided to continue using a move conventional static weir structure. This was assumed to be a reasonable approximation as despite inaccurate heads, as shown later the flow data was relatively similar, which was of most interest to modelling the operation of the movable weir. Furthermore, when the weir is in operation, it is planned that very little water passes through Allington weir; therefore the sluice gates would be either very slightly open or closed. As a consequence the sluice would act in a similar fashion to a conventional static weir, and therefore would not have a large impact on the model results.
20.3.2 Modelled River Flow 20.3.2.1 Low Flows The second parameter to be assessed was the river flow rates. In order to perform an evaluation of this, the modelled river flow was compared to the gauged flow at Allington. The first section of this evaluation looked at low flow conditions seen in the drought of 2012 between the 10th of March and 17th of April to determine how accurate a representation of the river the model provides. Flows were assessed for both U- and V-shaped river profiles to check which produced more accurate results.
From the results shown in Figure 20-7 the cross section of the river doesn’t have a significant impact on the overall flow of the river. As a consequence there is very little difference in accuracy between the two models for low flows. However when comparing the flows the gauged flow does seem to be somewhat lower than the simulated flow. One factor in this may that in a period of drought there are greater losses in the system, including evaporation and infiltration. As there are a number of gauging points in the section of the river modelled it was hoped that flow data could be obtained for two abstraction points between which there was no significant inputs from tributaries or through abstraction, such as between Maidstone and Allington Marina gauging stations. As a consequence it was not
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possible to make such loss calculations. However on the whole the simulated and gauged flows do follow are roughly similar pattern to that of the gauged flows with an average error of just under 13%.
3
2.5
2
1.5
1
0.5 MeanDailyFlow(m3/s) Gauged flow V shape U shape 0 0 5 10 15 20 25 30 35 40 Days Since 10/03/2012
Figure 20-7 A comparison of gauged and simulated flow (for U-and V-shaped river profiles) between March 10th and April 17th 2012 (Mean Gauged Flow=1.887m3/s)
Table 20-2 Error in model under drought conditions 0.241897 0.242974 Mean Error (m3/s) Mean Error % U Shaped 0.241 12.8 0.241897 0.242974 V Shaped 0.242 12.9
20.3.2.2 High Flow The results for high flow rates found are shown in Figure 20-9, which show that generally the modelled flows roughly followed the gauged flow. There are a few cases where the modelled flow falls somewhat below the recorded flow. The results also seem to show that a U-shaped river channel produces more accurate results than the V-shape. While most of the time these produce similar flows, at peak flows the V-shaped channel significantly overestimates the flow of the channel whereas flows for the U- shaped follow the flow patterns much more closely. This is reflected in the average accuracy of the two channels as shown in Table 20-3 where the error of the U-shaped channel can be seen to be around 6% less. Whist the error for of both models is over 20% the flow rate the variation for the U-shaped channel model does have a reasonably similar variance to the gauged. Furthermore, as there is still significant uncertainty due to estimations about the river system due to lack of data, the U-shaped channel model seems to be the best given the data available.
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200 U Shape 180 V Shape 160 Guaged 140 120 100 80 60
MeanDaily Flow(m3/s) 40 20 0 12-11-09 26-11-09 10-12-09 24-12-09 07-01-10 21-01-10 04-02-10 18-02-10 04-03-10 18-03-10 01-04-10 15-04-10 Date
Figure 20-8 Comparison of modelled flow rates with different river profiles against gauged flow for high flow rate conditions in winter 2009/10
Table 20-3 Error in model under drought conditions
Mean Error (m3/s) Mean Error % Average Flow (m3/s) Flow standard deviations U Shaped 6.437 21.6 24.51 29.58 V Shaped 8.205 27.5 26.4376 35.49 Gauged N/A N/A 29.8466 27.68
29.57932 35.49199 27.67537
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20.4 Weir Operation
One of the primary aims of the model is to determine the best operational parameters of the weir to control the river flow in order to get the highest abstraction volume from the river. During a tidal cycle, there is a period of time where the natural flow of the river exceeds the minimum residual flow, as shown in Figure 20-9. The aim of the weir’s function is to effectively slow down the flow during the period of high flows, ideally to just above the minimum residual flow. As a consequence when in normal situations the natural flow would fall below the minimum residual flow, the presences of the weir creates a higher water level upstream of the weir allowing flow rates above the minimum residual flow to be maintained. As a consequence it is then possible to increase the downstream flow out of the reservoir until the water levels on both sides of the weir are equal when the reservoir is essentially empty. At this point the weir will either continue to drain if the weir empties before low tide and water is flowing out of the estuary or start to refill if the weir empties after low tide when water is flowing back into the estuary.
40 Natural Flow Minimum Residual Flow 30 20 10 0
Flowm3/s 0 3 6 9 12 15 18 21 24 -10 -20 -30 Time (hours)
Figure 20-9 Natural flow of the River Medway at the point on the river where the moveable weir is to be placed
However when considering the gate operation there are some prerequisites that limit the time the gate can be deployed. In order to allow the river to be navigable it was decided that instead of having the extra expense of constructing a lock next to the weir it would be preferable to limit the time of operation of the weir, so as a consequence the weir cannot be fully deployed at high tide.
20.4.1 Sluice Gate Operation For the design of the sluice gate chosen there are three main stages of operation, an un-obstructive stage where the sluice gate is below the river bank and doesn’t affect flow, a fully deployed stage where the
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sluice gate is at its peak height (shown in Figure 20-10) and a transitions stage between the two states. Furthermore for the movement of the sluice gate must be proportional to the river level downstream of the weir. In order to use the model to calculate the best operation of the weir (i.e. the one that allows for the most abstraction) there are three parameters that need to be calculated. These are the height of the weir above the bank at full deployment and the downstream river level when the gate is fully deployed and when the gate starts to deploy. This operational behaviour is shown in Figure 20-11.
Figure 20-10 Diagram showing the position of the sluice at maximum and minimum extent (Jessica Hyland)
3 2.5 2 1.5 River Level (mAD) 1 0.5 0 Height of the bottom of the Height(m) -0.5 0 6 12 18 24 30 weir above the river bed -1 (m) -1.5 -2 Time (hours)
Figure 20-11 Diagram showing the relative deployment of the sluice gate with the downstream river level
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During the sluices operation, if the flow exceeds the minimum residual flow, the abstraction point placed just before Allington was set to abstract a volume of water equal to the total flow upstream of the abstraction point. If flow through the new movable weir fell below the minimum residual flow then in line with regulations all abstraction would stop. Overall it was assumed under the low flow conditions when the sluice is operational, the flow of water over Allington would have little impact on the overall flow out of the reservoir, which would be dominated by the tidal influences. As a consequence the best abstraction strategy would be to take as much water from the river as possible whilst the flow over movable weir exceeds the minimum residual flow.
20.4.2 Testing the river flow The first parameter tested was the height of the gap between the sluice gate and the river bed when the gate is fully deployed. In this experiment the weir was set to be fully deployed at all times. In order to get a baseline abstraction volume, the system was also tested when the gate was never deployed, hence caused no obstruction to flow. Abstraction volumes were calculated for flows during the summer of 2010, between 1st of June and 31st of August. During this period the integral of the flow rate over time is calculated to find the total volume of water abstracted in m3 (m3/s x s). The value is then converted into mega-litres (ML) and averaged to find the daily abstraction rate.
From the results shown in
116 114 112 110 108 106
104 Abstraction(ML/day) 102 100 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Height of gate above river bed (m)
Figure 20-12 it was found that the best opening height for the weir was 0.25m. Lower heights caused the volume of abstraction to drop off significantly, with this gate configuration slowing down the flow through the sluice too much causing the flow to fall below the minimum residual flow. This problem occurred to such a degree that the volume of abstraction fell below the baseline abstraction volume
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(110.2ML/day) possible when the gate is never deployed to around 100.8ML/day. With the gate positioned at a height greater than 0.25m it was found the volume of abstraction tailed of as the weir fails to slow flow at high flows, hence resulting in the high flows not being held above the minimum residual flow for as long a time.
116 114 112 110 108 106
104 Abstraction(ML/day) 102 100 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Height of gate above river bed (m)
Figure 20-12 The average volume of water abstracted from the Medway for different heights of gate opening for the summer of 2010 (1st June-31st August). Baseline abstraction when the weir is not deployed was calculated as 110.2 Ml/day
20.4.3 Gate Deployment The second part of the assessment of the sluice’s operation was to find optimal transition behaviour for the gate. As the weir operates using buoyancy, the tidal water level downstream of the sluice determines when the weir starts to come into operation and when it is fully deployed. In order to calculate the optimum time for this a number of different transition times were used. The two parameters that were tested was the river level at which the sluice gate is fully deployed and the difference in river levels between the gate starting to be deployed and it becoming fully deployed (transition depth change). As mentioned before, to allow for navigation the weir cannot be fully deployed at high tide so therefore a compromise must be made between abstraction and navigation
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115 114 113 112 111 110 109 108
Abstraction(ML/day) 107 1m Transition 0.5m Transition 106 105 0.4 0.9 1.4 1.9 2.4 River Height at the Start of Deployment
Figure 20-13 A comparison of the abstraction volume for various values of the sluice gates deployment depths. The graph compares the different heights at which the sluice gate goes fully into operation and the change of river depth required for the weir to move from being un-obstructive to full deployed.
The results from this test can be seen in Figure 20-13, showing the changes in volume of abstraction possible with the different gate operations described, and with different transitions depths changes of 50cm and 1m. From these calculations the depth at which the sluice gate becomes fully deployed doesn’t make a huge amount of difference to either transition depth in terms of the volume of water that can be abstracted, when the weir becomes fully deployed before the river falls below 0.4m above datum (i.e. river height at start of deployment plus transition depth). However, when deployed after this point the river flow the abstraction volume falls below the baseline 110ML/day that can be abstracted when the weir is not in operation. As a consequence the lowest river height the weir can be deployed at is 0.9m with a transition depth of 0.5m. As shown in Figure 20-14 at neap tide this provides a 6 hour window centred on high tide where the weir is not deployed. Consequently, the weir operation selected can be confirmed to meet the requirements for navigation for a setup with no weir (as described in the proposed locations) operating at near optimum performance.
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2.5 Downstream river levels at the 2 Movable Weir 0.4mAD 1.5
1 0.9 mAD
0.5
River Level (mAD) 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 -0.5 Time
Figure 20-14 The change of river levels at neap tide with respect to weir deployment heights
20.5 Droughts and future flows
In order to evaluate the feasibility of the weir it is important to know how well it functions in allowing extra abstraction to take place in cases of reduced flow, when it will be most needed. This will allow for a comparison of its operation with alternative methods for increasing the amount of water available for abstraction. The first scenario tested looks at how the system works under severe drought conditions, for which the 1976 drought has been chosen. In addition it also looks to evaluate how much extra water the movable weir will allow to be abstracted from the river in the future, taking into account both reduced flow conditions and changes in sea level. This allows an evaluation of how much extra abstraction the system will allow for during its lifetime.
20.5.1 1976 drought In order to assess worst case drought conditions the drought in the summer of 1976 was used. This is identified in Southern Water’s drought plan (Southern Water, 2013) as one of the most significant historical droughts in the past century. From the river flow data at Teston, the 1976 drought see one of the longest spells of very low river levels since gauging began in 1956 River levels fell below 1m3/s for weeks at a time in January and February and over the summer from June to the beginning of September.
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20
15
y = 8.5831x 10
5
Flowsrates for Teston (m3/s) 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Flow rates for Lenside (m3/s)
Figure 20-15 A comparison of river levels at Lenside and Teston from 20/12/1984 till 30/09/2013 (where data is available for both the Lenside and Teston)
For this drought case flow data was only available for the Medway and not the Len. As a consequence it was necessary to predict likely flows of the Len from those of the Medway. In order to do this, flows for the river Medway at Teston and for the Len at Lenside where compared. The initial plot of these two variables in Figure 20-15 showed there was significant variation around the linear line of best fit between the two variables. In order improve the correlation, comparisons of flows were undertaken on a month by month basis, with graphs shown in the appendix. This approach was used as it helped to limit the variations in evaporation and precipitation that may affect the flow of the two rivers differently in different months. From the lines of best fit it was found that there was a slightly different correlation between flows for the two rivers for each month. The lines of best fit found would then be used to predict flows on a month by month basis.
40 20 0 1968 1974 1980 1986 1992 -20 -40 Flowtheat (m3/s) Summer 1976 Summer 2010 -60 Hours since 1st June 00:00
Figure 20-16 an extract of movable Weir for Flows during summer 1976 at the lowest flows of the period compared with flows for the same period during the summer of 2010
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With tidal data kept the same the flow rates through the Movable Weir appear to be largely invariant to the downstream flow conditions. From a representative extract of the results shown in Figure 20-16, differences between flow in the 1976 drought and the summer of 2010 only become pronounced at peak negative flows, with flow being roughly similar for positive flows. Overall there was an average difference of 0.49m3/s between the two flow values for positive flows increasing to 1.84 m3/s. However despite the flow rates around the weir the abstraction volume was significantly less, falling from around 114ML/day to 36.573 ML/day. However due to the consistency of flows at the movable weir the reduction in abstraction for the flows was caused by a lack of fresh water available to abstract when flow rates are lower.
20.5.2 Future reduced Flow The second test case for the model tested the system under future flow conditions. The predictions performed were based on two different time period, the extreme drought of the summer of 1976 and the more typical summer of 2010. In order to estimate future flows the pre-existing predictions of relative change of flow of the river Medway from an academic paper (Cloke, et al., 2010) were used to project forward low flow conditions. The same factor of change of flow was also used for the input from the River Len. In this paper flow predictions are made for 3 future time periods, 1990-2020, 2020- 2050 and 2050-2080 hence these three time periods were also used for these predictions of abstraction volumes.
In addition the changes in tide levels in the Medway caused by increasing sea levels were also investigated. As there were no records of the change in past tidal river heads compared to changes in sea levels or predictions of future changes in heads at New Hythe a more simplistic method of prediction was used. All downstream tidal heads were increased by a value equal to specified rises in sea levels for the eastern coast of the UK by the Environment Agency’s Medway Estuary Management Plan (Environment Agency, 2010, p. 35). In order to evaluate how much of an effect the changing tide had on the volume of water that can be abstracted the tidal head data specified in the 2006 Admiralty Tide Tables was used as a control.
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Table 20-4 A comparison of Abstraction volumes for projected flow conditions for two summer conditions
Averaged abstraction volume for stated time periods (ML/day) and average flow at Teston (m3/s, in brackets) 1990-2020 2020-2050 2050-2080 2010 style summer 113.9 (2.592) 96.8 (2.284) 60.7 (1.368) 1976 style drought 32.5 (0.783) 28.9 (0.682) 18.3 (0.427) 2010 style Summer with increased tides 113.9 (2.592) 96.8 (2.284) 59.6 (2.284) 1976 style drought with increased tides 32.5 (0.783) 28.0 (0.682) 18.0 (0.682)
20.5.3 Analysis From Error! Reference source not found. it can be observed that there is a significant decrease in the amount of water that can be abstracted using the estuary reservoir to just over half its previous volume across the time periods modelled. This shows that it potential of the sluice for increasing abstraction is still limited by the volume of fresh water available in the river. However comparing the abstraction figures it appears that a change in the sea level has little effect on the volume of abstraction possible.
However, in order to evaluate the volume of abstraction possible, the modelled values can be compared with the overall volume of water abstracted at Allington, as stated in the Medway Catchment Management Scheme (Environment Agency, 2013, p. 19). The value stated as the current approximate volume available for abstraction during high flows is 100ML/day. During a 2010 style summer, the abstraction that the proposed system allows is similar or greater to that value until the period 2050- 2080, when the volume drops significantly. In a severe drought such as in 1976 the water it is possible to abstract under roughly current day conditions is only a third of the current approximate abstraction rate, falling to under 20% in future conditions. However, this is still a significant volume of water, comparable with those available for other potential schemes that southern water have suggested for maintaining water supply. One such suggestion for a system that allows the processing of waste water for reuse aims to produce around 20ML/day of water (Southern Water, 2014, p. 181), which is comparable to the worst case abstraction volumes. Overall, this would suggest that in a typical summer the system works well but is limited to a smaller but still significant value during lower river flows. Overall it appears to be a valuable tool in ensuring increased water resources is available in the future.
20.6 Conclusions
From the report, optimal parameters for the operation of the weir were found, with the weir starting to deploy when the river fell below 0.9mAD and became fully deployed at 0.4mAD. This was shown to
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allow for a window of 3 hours either side of high tide where the weir was not deployed. As described in the location considerations this is sufficient window for boats leaving Allington within its navigable time to be able to pass over the weir location before deployment without a need for a lock. In addition, the chosen gates operation was shown to have only a minor impact on the volume of water it is possible to abstract compared with earlier deployment.
Furthermore, changes in the sea levels and flows rates over Allington and was found to have little impact on the operation of the weir, demonstrating its invariance to changes in climate. However, as the system still relies on abstracting fresh water from the river, the abstraction rate inevitably decreases as flow rates in the river decrease. From the abstraction volumes found, even in the worst case scenario of a future 1976 style drought, where flow rates are further reduced by decreasing river flows that a significant volume of water (18ML/d) can be abstracted. In best case scenarios, the system allows for an average abstraction rate at Allington during low flows of greater than the estimated current rate at high flows (113.9ML/d vs 100ML/d). Overall, it would seem to provide an effective system for allowing for additional abstraction from the Medway.
20.7 Future Work
There are some limitations to the results found. As the abstraction methods used are significantly greedier. As a hands-off flow is not observed over Allington but at the new movable weir a considerably greater amount of water in the river is abstracted in the proposed scheme than is currently. As a consequence this may result in a deterioration of water quality. This may mean the water requires more treatment, or there will have to be a reduction of the water abstracted to less than the maximum in order to have an acceptable level of water quality. Therefore a more detailed investigation into this area would be required to get a more comprehensive view on the effectiveness of the system. Furthermore, whilst the model produced gives a reasonable approximation of abstraction volumes, further study would benefit from improved data. This could include the more details of the structure river channel, the gauged tidal river levels and structure and operation of the weirs would be required. Gauged river level or flow data from the tidal section included in the river model would be particularly valuable as it has not been possible to evaluate the accuracy of this section of the river. However, given the evaluation of the model undertaken, whilst there still are inaccuracies, the river flow over Allington does provide a reasonable approximation of the flow over Allington. As a consequence, the results produced should provide a sensible approximation of abstraction rates.
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Environmental Impact Assessment 21.1 Purpose of the Environmental Impact Assessment (EIA)
The environmental impact assessment (EIA) ensures that the likely significant environmental effects are identified and assessed before a decision is taken on whether a proposal is allowed to proceed. The design of the project can then be guided to avoid or minimise the identified environmental impacts. The process of an EIA is shown in Figure 21-1 below.
Figure 21-1 Key steps in the EIA process (Environment Agency, 2002)
The EIA would be carried out in line with the process and relevant methodologies laid out by the Agency Area Office in Figure 21-1. However this process is extremely in depth for the purposes of a
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feasibility study. Therefore a new mitigation plan was devised which was deemed appropriate for this investigation.
The plan will attempt to undertake the following practical hierarchy of mitigation as shown in Figure 21-2 below. Where appropriate mitigation had been undertaken at the design stage such as having a movable weir instead of a static weir which could provide difficulties to fish populations.
Avoid •Avoid the feaure that would lead to an imact at the design stage impacts at souce
•When impacts cannot be avoided, design changes should be made in order to Reduce reduce (minimise) the impact impacts at source
•For impacts that can niether be avoided or reduced at the design stage and those Abate that have been reduced can be abated at source. impacts at the source
•Impacts remaining after the first 3 stages of mitgation should be considered for Abate abatement at the source. impacts at receptor
•If impacts remain, ways should be consiered in order to repair an damage that will Repair occur. impacts
•Where repair is deemed to not be possilbe compensation for whatever loss is Compensat incurred will be appropriately provided. e in kind
Compensat •When all other precedding methods have failed and appropriate compensation e by any cannot be met, compensation above and beyond should be provided. means and enhance
Figure 21-2 Hierarchical Mitigation Process (Environment Agency, 2002)
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This plan shown in Figure 21-2 will be used when looking at environmental factors which will be affected due to the inclusion of a new weir in the river Medway. As this study is a feasibility study emphasis will be put towards how severely a factor is affected and if anything can and should be done to mitigate it at the design phase
21.2 Environmental factors of the EIA
The building and eventual installation of the movable weir presents impacts to many different environmental factors. The key environmental factors that will be discussed and the effects on them are as follows; (Rickard, et al., 2003)
Archaeology Conservation and heritage Fish migration Flora and fauna Land drainage and flood defence Landscape and ecology Navigation Recreation and amenity Sedimentation and erosion Water resources and water quality
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The impacts, nature and significance of the topic areas will be presented in Table 21-1 which will concisely display the relevant information for this feasibility study. Environmental factors such as fish migration, flora and fauna, water quality are discussed in more detail in the section after the summary table. Table 21-1 will display the impact to these environmental factors within the Medway estuary which is shown in Figure 21-3.
Figure 21-3 The Medway Estuary (Wildlife-Trust, 2006)
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Table 21-1 Summary table of the environmental factors which are impacted in the Medway estuary
Topic Area Description of Geographical Impact Nature Significance Impact Mitigation Measure Impact Impact Level of Issue score score with Importance before mitigation mitigation in place R D L Effects on the Medway Estuary upon usage of the movable weir Archaeology Effects on Adverse Lt, IR Major High Ensuring that the Low archaeological changes in water flow sites in the due to the inclusion of a Medway estuary new weir upstream from such as the estuary will not Prehistoric drove impact any of these ways, archaeological sites. This Roman pottery will be done by ● kiln designing the weir to Sites and Anglo ensure that water flow Saxon fish traps into the estuary is (Medway Council, similar to what it is 2012) currently. This flow will also be monitored once the weir is in place to provide further results. Conservation Changes in the Adverse St, R Minor Medium Design will be Low- & Heritage water quality due undertaken in order to Medium to a new weir can reduce the impacts of effect rare any changes in water conserved species ● quality, with any such as the changes being within Golden Samphire the acceptable range for (Medway Council, the species concerned. 2011)
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Effects on the Adverse Lt, IR Minor High Design will be carried Low Medway estuary out to ensure the is a heritage site estuary is not effected having both greatly in terms of its international and environment. Effects to ● national the economy are not significance in applicable in this case. terms of the environment and the economy. Fish Migration Disruption to fish Adverse Lt, R Major Medium - Checks will be carried Low – populations High out in order make sure Medium within the there are no unneeded Medway estuary disruptions to fish and to fish populations. This is populations that ● mainly due to the fact will migrate that the weir is only in upstream from operation during the the estuary. summer months and that it rises and falls with the tide. Flora & Fauna Disruptions or Adverse Lt, R Major Medium - Local flora and fauna Low changes to any High habitats within the flora in the estuary have been Medway estuary checked in order to make sure that any changes are within an ● acceptable range. Once the weir is in place more research will be conducted to substantiate this claim. If habitats are affected
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to outside this safe range then they will be relocated appropriately. Land Drainage Impacts toward Adverse St,R Minor Low This is initially a very low Low and Flood land drainage and risk as the estuary is Defence flood defences already a “flooded” environment and has the necessary flood defences in place ● (Medway Council, 2011). Even with the inclusion of the tidal weir the defences are suitable. Land drainage in the estuary is dictated by the tide. Landscape and Adverse impacts Adverse Lt, IR Major High Mitigation was Low Ecology towards the undertaken at the landscape of the design phase in order to estuary assure there would be no change to the ● landscape of the estuary. The tidal weir upstream will not change the landscape of the estuary. Changes in the Adverse Lt, IR Major High Organisms have already Low conditions of the been checked in order ecologies within to ensure they can the estuary ● survive if the environmental conditions changed slightly with the
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inclusion of a tidal weir. Therefore the interactions between these organisms are assumed to remain as they are currently. Further research will be conducted Navigation Disruptions to Adverse Lt, R Minor Low The inclusion of the tidal Low navigation weir upstream will not downstream of have an effect on the weir in the navigation downstream estuary. in the estuary. At the weir the navigation regulations match the ● regulations in place at Allington, therefore anyone wanting to sail there will be familiar with the rules and can adjust when the new weir is installed. Recreation & Disruption to Adverse Lt, R Major Medium - Recreational activities Low Amenity recreational High mainly occur within the activities within estuary and during the the estuary such winter months (Medway as boating, fishing Council, 2012). This is and the use of ● when the movable weir personal water is not in operation. Even craft (Medway during the summer Council, 2012). months when the weir is in operation recreational activities
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should be unaffected as the weir is not a direct hindrance to these activities. Sedimentation Increased or Adverse Lt, IR Major Medium With the inclusion of a Low & Erosion unwanted weir upstream it is sedimentation & unlikely that erosion occurring sedimentation & erosion in the Medway will increase within the estuary. estuary as there is no “extra” water being put into the system to allow ● this to occur. During the design phase it was decided that the only water being impounded within the tidal weir is water that would always naturally flow back into the estuary. Water Adverse changes Adverse Lt, R Major Medium - Within an estuary daily Low – Resources & to water quality High and monthly changes in Medium Water Quality within the water quality are estuary. common (Oberrecht, 2010). As the tidal weir is only in operation ● within the summer months and is in the tidal section of the river changes to water quality in the estuary are unlikely. However once the weir is in operation
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then further research can be conducted in order to see if this statement holds true. Changes to water Beneficial Lt Major N/A The installation and N/A resources within operation of the new the area. tidal weir during the summer months will allow the water companies to use ● freshwater that would normally be used to maintain the natural flow of the river to be used elsewhere within the district.
Key:
R Regional D District L Local St Short term Lt Long term R Reversible IR Irreversible High - Anything irreversible and at a regional level Medium - high Long term and reversible and short term irreversible Medium - Anything at a district or local level that is long term Low - Short term at local or district
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21.3 Fish Migration
Species Stage January Febuary March April May June July August September October November December
Bass Juvenille
Thick-lipped mullet Adult
Black Goby Breeding
Common Goby Breeding
Sand Goby Breeding
Sandeel Adult/Juv
5 Bearded rockling Adult
Flounder Migration
Juvenille Flatfish Juvenilles
Thin-lipped mullet Adult
Eel Adult
Immigrant
Emigrant
Twaite shad Breeding
Allis shad Breeding
Smelt Adult/Fry
Salmon Immigrant
Emigrant
Sea Trout Immigrant
Emigrant Figure 21-4 Critical periods for fish species in the Medway Estuary. Data from (Environment Agency, 2013)
During the initial design phase of the weir for this feasibility study it was acknowledged that fish migration may pose a problem. Particular species of fish migrate from the estuary upstream towards the freshwater part of the river for breeding and spawning purposes. This problem would have to be dealt with, one option would have been to add a fish pass along the route that would be blocked by the weir structure. To keep in line with the brief the weir would only have be operational during the summer months but would unfortunately it would block the river way all year round. During design an idea of using a movable weir which would fall and rise with the tide was proposed. This weir would also be
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stored in the river bed when not in use. This innovative design allowed the river way to not be permanently blocked all year round as would happen with a static weir structure. The critical time periods for fish species within the Medway estuary can be found in
Species Stage January Febuary March April May June July August September October November December
Bass Juvenille
Thick-lipped mullet Adult
Black Goby Breeding
Common Goby Breeding
Sand Goby Breeding
Sandeel Adult/Juv
5 Bearded rockling Adult
Flounder Migration
Juvenille Flatfish Juvenilles
Thin-lipped mullet Adult
Eel Adult
Immigrant
Emigrant
Twaite shad Breeding
Allis shad Breeding
Smelt Adult/Fry
Salmon Immigrant
Emigrant
Sea Trout Immigrant
Emigrant
Figure 21-4 the fish species displayed in Figure 21-4 can be separated into three different categories which will allow a clearer understanding of which fish would be affected.
Marine fishes – This includes the Bass and the Thick-lipped mullet. This type of fish spend all their life feeding and growing within the brackish estuarine waters (B.N.Austin, 1996). Therefore marine fish are unaffected by the new weir. Catadromous species – This includes the Flounder and the Eel. This type of species must breed in the sea and migrate towards the estuary in order to feed (B.N.Austin, 1996). Therefore this species is also unaffected by the new weir.
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Anadromous fish – This includes fish such as Salmon and the Twaite. This type of fish must breed in the fresh waters and will spend the rest of its life feeding within the estuary and at sea. Therefore anadromous fish may be affected by the new weir. However since the movable weir rises and falls with the tide it should allow anadromous fish that require fresh water for breeding during the summer months to pass.
21.4 Flora & Fauna
The Medway estuary is a vast location with many different species of flora & fauna but it can be broken down in 4 smaller ecosystems as shown in Figure 21-5.
Figure 21-5 Medway Estuary divided into smaller ecosystems (Medway Council, 2011)
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Grazing marsh – Grazing marsh was given a risk rating of medium/low because this area is mainly an area of pasture where farm animals are released to feed as shown in Figure 21-6 (Medway Council, 2011). Therefore any adverse changes in water quality could affect the grazing animals. However water quality changes to the extent at which it could affect these animals is extremely unlikely. Further research will be conducted into this area once the weir is in operation to ensure no changes
Figure 21-6 Cattle grazing near Allhallows at the Medway estuary (Medway Council, 2011)
Inter-tidal mudflats – This habitat exists between high and low tide and is completely covered by water twice a day as the tide rises and falls. The mud itself is packed full of important invertebrate life (Medway Council, 2011). However since this habitat is mainly dependent on the incoming tide for its conditions it is highly unlikely that an upstream weir would have any effect, therefore this area was given a risk rating of low. Salt marsh – This habitat is flooded occasionally and therefore only supports special plants such as sea aster and cordgrass, these types of plants are able to cope with being completely covered by salt water (Medway Council, 2011). Therefore any changes which increase or decrease the salinity of this area will not disturb the local plant life, therefore this area was given a risk rating of low. Sea walls – The estuary is protected in many areas by sea walls which are designed to keep the river in its place and limit flooding. Large areas of plant life have formed on the mud sections of the sea walls which are adapted to more saline conditions within the estuary (Medway Council, 2011). This plant life is accustomed to salty water conditions and it therefore given a risk rating of low.
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21.5 Water Quality
The inclusion of a movable weir within the tidal section of the river Medway could have consequences for water quality. The two properties of water that are of interest are salinity and dissolved oxygen content.
Salinity measures how much dissolved salt there is present within a certain mass of water and differs depending on the position of the river from source to estuary to sea. The movable weir will be installed within the tidal section of the river Medway. Therefore the type of water that will be impounded by the movable weir will be mixture of salt and fresh water this can be seen in Figure 21-7.
Figure 21-7 Typical river profile with regards to salt and fresh water interactions (Oberrecht, 2010)
The characteristic differences between fresh and salt water, mainly density, dictate how the two blend and mix. However sometimes due to these differences they may not mix at all, they instead stratify and form layers. Circulation of fresh and salt water in the area highlighted in Figure 21-7 is affected by tide, rainfall, river inflow, evaporation and the wind. Considering the conditions at the river Medway and after analysing results (Cutting, 2014, shown in Appendix E) the estuary at Medway can be classified as a salt-wedge estuary; this is shown diagrammatically in Figure 21-8.
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Water Surface
Fresh
Salt
Bottom Figure 21-8 Salt-Wedge estuary with a sharp density interface boundary layer (shown in red) In this type of estuary there is a distinct boundary layer with a sharp interface. This doesn’t allow much mixing between the two types of water. River water dominates in the salt-wedge estuary model, whilst tidal effects have a much smaller impact on the circulation patterns. As the new weir will only be impounding tidal water, and with no fresh water going over Allington weir during this time, the salt-wedge estuary model is can be assumed to occur within the impounded water. The assumed layout of the impounded water if the water is allowed to ‘settle’ can be seen in Figure 21-9.
Allington Weir New movable weir
River bed
Figure 21-9 Assumed layout of the impounded fresh and salt water
Once this water is released it conforms to the regime of the rest of the tidal section towards the estuary. This assumption and model only occurs and applies to the summer months, this may cause a slight salinity increase during these months as no new freshwater is crashing over Allington weir. However for this feasibility study this change should be negligible and be cancelled out by allowing fresh water to crash over during the rest of the year. It is recommended that further research should be conducted during the summer months after the weir is in operation to verify this assumption.
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Dissolved oxygen content measures how much oxygen is dissolved within a certain body of water. This property is vital for organisms within the water that need the oxygen to thrive. It is known that flowing water dissolves more oxygen than still water which is due to the crashing and churning nature of it. If the impounded water shown in Figure 21-9 is held for an extended amount of time then the amount of dissolved oxygen within it could become an issue. However due to the innovative design of the new tidal weir which allows it to rise and fall with the tide this extended amount of time issue shouldn’t be a problem. Also during the non-summer months water will be crashing over Allington weir which will increase the amount of oxygen in the water if it has decreased over the summer months.
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The following table shows the summary of the Environmental impact assessment carried out.
Table 21-2: Environmental Impact Assessment
Topic Description of Impact Geographical Impact Nature Significance Impact Mitigation Measure Impact Area Level of Issue score score with Importance before mitigation mitigation in place R D L Installation of the movable weir in river Human Noise during ● Adverse St, R Minor Medium - Starting and stopping Low Beings construction and Low work at appropriate hours installation (9-6) and move weir to a more secluded location further away from residential areas Increase of traffic on ● Adverse St, R Minor Medium Ensure that delivers and Low roads by large vehicles the transportation by larger vehicles is done outside of the local high traffic periods Soil & Removal of soil to ● Adverse Lt, IR Minor Medium Design will be carried out Low - Geology change river bed shape to ensure the removal of Medium for the installation of the least amount of soil the weir Disruption to soil by ● Adverse Lt, IR Major High Concrete will be used to Low – Eddy currents reinforce the river bed and medium introduced by the embankments to reduce addition of the weir the erosion along the river
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Topic Description of Impact Geographical Impact Nature Significance Impact Mitigation Measure Impact Area Level of Issue score score with Importance before mitigation mitigation in place R D L Collection of ● Adverse Lt, R Minor Medium Maintenance will be to be Low sedimentation upstream ensure the removal of any excess sediment so that it does not cause any adverse effects Water Composition of water ● Adverse LT, IR Major High Salinity checks will be Low – could be compromised carried out to ensure that medium with the addition of the the water composition will weir, affecting the state not be greatly affected and of the river; its soil, thus not affect the flora and fauna and the surrounding environment. surrounding geology Monitoring well be and businesses that undertaken once the weir abstract water for use is in operation to check in their processes for changes in salinity over the life of the operation of the weir Energy During the life of ● Adverse Lt, R Major Medium - The design of the weir Low usage movable weir the High will be such that no or movement of the weir minimal energy will be will use energy and use used in the operation of carbon. This will add to the weir the greenhouse gases Flora & Disruption to stream ● Adverse Lt, IR Major High The habitats that will be Low Fauna side habitats affected will be relocated to new stream side habitats the have simpler environment to ensure that fauna are not adversely affected
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Topic Description of Impact Geographical Impact Nature Significance Impact Mitigation Measure Impact Area Level of Issue score score with Importance before mitigation mitigation in place R D L Hydroelectric energy production installation Flora & The flow of water ● Adverse Lt, IR Major Medium - Inclusion of concrete Medium - Fauna disturbed High bedding to dissipate the Low flow in the river and encourage more laminar flow Water Disruption to fish ● Adverse Lt, IR Major Medium - Addition of fish pass that Low pathways stopping High will enable fish to be them from travelling to directed out of the path of breeding area the hydro unit depending on the location of the unit. Effect on the local ● Adverse Lt, IR Minor Medium - As the weir has been Low groundwater regime High constructed below the terminal weir and is located in the estuarine part of the river then there will be no adverse effect on the current groundwater supply but a more in-depth investigation needs to take place to ensure this is the case Installation of the new abstraction pipeline and pump
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Topic Description of Impact Geographical Impact Nature Significance Impact Mitigation Measure Impact Area Level of Issue score score with Importance before mitigation mitigation in place R D L Flora & Disruption to habitats ● Adverse Lt, R Major Medium - Perform an investigation Medium – Fauna High to determine where Low potential habitats may be. Move the path of the pipeline out of the way of the habitats. If this cannot be done ensure that new habitats are provided and animals are moved without harm. Disruption to Flora as ● Adverse St, R Major Medium Investigation of potential Low pipes are installed protected Flora and where possible ensure that the pipeline is placed outside the boundary of such areas. All flora disrupted during the installation of the pipelines will be removed with care and placed back in as far as possible. Where trees are removed new trees will be planted in the surrounding area. Soil & Disruption to soil for ● Adverse St, R Major Medium - All soil removed will be Low Geology the placing of the High placed back and pipelines compacted and that which cannot be placed back will be removed
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Key: R Regional D District L Local St Short term Lt Long term R Reversible IR Irreversible High Anything irreversible and at a regional level Medium - high Long term and reversible and short term irreversible Medium Anything at a district or local level that is long term Low Short term at local or district
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Hydro-installation
While the threat of global warming and climate change is becoming more of relevance than ever, worldwide power consumption and oil prices are rising continuously. As a result, the generation of renewable energy is holding a position of high priority in the government’s subsidy and promotion list with the hope to help maintain a balanced climate (Oil Change International, 2015).Nowadays, hydro- power generation can be considered as one of the most effective and established ways of producing renewable power. By installing a hydro-unit plant at a location where flowing water is present, the kinetic energy in the flow can be harnessed and simply converted to electricity with the help of a turbine that drives a generator. Depending on the type, hydro-power units can produce down to no green-house gas emissions but could result harmful to the water quality, local ecology and a risk to migrating fish (Landustrie, 2012).
As previously mentioned in the report, the project aims in providing a cost and energy saving solution to immediately reduce the intensity of pumping by efficiently using the flow of water at the location where it is available. Hence, it would only be appropriate to look into the feasibility of installing a small-scale hydro-power plant which could potentially contribute in the reduction of carbon dioxide
(CO2) emissions and the operating costs of the scheme. Sites of potential for hydro-installation close to the location of the movable weir and suitable turbine schemes are studied in order to get an accurate theoretical value of the power output capacity. The initial and operation costs of the studied schemes are estimated and related to the income to obtain from the electricity to be generated. The efficiencies and CO2 savings of each scheme are assessed and an understanding of the cost/benefit ratios will allow for the schemes to be deemed feasible or not.
22.1 Description of Proposed Locations
Initially, the aim of this feasibility study was to identify whether it would be advantageous to install a hydro-power unit for the purpose of providing electricity to the mechanism of the movable weir. However, it was then decided that the design appraisal of the movable weir will present a self-regulating option which does not require any electricity to function. Therefore, the locations that had already been proposed for the initial purpose are finally studied for selling electricity directly to the grid in order to help bring down carbon dioxide emissions and pumping costs.
Each of the locations chosen are assessed by following the criteria listed and explained below and passed for studying if the criteria are adequately met.
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1. Site Accessibility: This criteria is divided into two sections. First, the site has to be able to provide ease of access and adequate space to incoming construction traffic for the initial delivery and installation of the turbine. Second, the spot of installation needs to be able to keep allowing access for continuous inspection and potential maintenance of the turbine. 2. Ease of Construction: The site needs to be able to allow the team and the contractor to install without requiring more heavy construction alternations to the existing structure and further costs than the common site. 3. Potential Power Output: The site must provide an adequate volume of water and height of river for utilisation and the flow conditions present need to be undisruptive to the operation of a potentially installed turbine.
For the purpose of undertaking this feasibility study, three locations for potential hydro-installation were identified in the proximity of the site where the movable weir is planned to be placed.
Figure 22-1 Proposed Site Locations (Google Maps, 2014)
22.1.1 Location 1 – Allington Weir Allington can be considered as the end point of flow-to-structure interaction downstream in River Medway. The site of Allington consists of a navigation lock and a mechanical weir of 4.65 meters in height which together add up to a total of approximately 40 meters in width as measured by using a satellite scaled map (Bing, 2014). Allington Weir consists of a series of mechanically operated sluice and lock gates which help in controlling the rate of the upstream flow going downstream and prohibit
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the tidal water downstream altering the upstream flow conditions (Environmental Agency, 2014). As this and the remaining sites are situated close to the top of the estuary of River Medway, the hydro- units installed are only going to be capable of utilising water volumes of this river.
Figure 22-2: Allington Weir (Geograph, 2013).
This is considered to be the most favourable site for hydro-installation and is further studied in the next steps. The site is easily accessible as routes already exist to the weir structure which could be used for the initial delivery and installation of the turbine and its associated components. Furthermore, as the weir is supposed to be mechanically operated, control housing is already present which could be easily modified for the continuous inspection and potential maintenance of the turbine by constructing a power house adjacently. The existing weir is at a very good condition and can be easily modified by introducing an intake on top and incorporating the turbine within the weir while providing control and protection through an automated sluice gate and screening. Finally, the flow and head conditions present on site are also considered to be the most favourable in comparison to the conditions on the remaining sites as the site provides the highest head and the tide can only affect the available head.
22.1.2 Location 2 – Downstream of Allington Weir This site is located directly below Allington Weir and close to the exit of Allington Lock. The advantage of this site is that it accumulates accelerated water from both the weir and the lock within a smaller river width of approximately 20 meters, resulting to a larger volume of water and a higher flow-rate per meter width. However, the location has the major disadvantage of lacking in supportive structures and that placing a hydro-unit could constitute a problem regarding the navigation of vessels.
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Figure 22-3: Allington Weir and Lock Exit (unknown boater, 2001).
This site is considered as the least favourable site for hydro-installation and will not be taken into account in further steps. Assuming that safe enough routes to the site do not exist, routes to Allington Weir would have to be extended in order to allow for the delivery and installation of the unit. In addition, since inspection and maintenance procedures would require a way to reach the turbine, which would be potentially placed towards the middle of the river width for ideal abstraction, the level of complexity in construction would be considerably raised. The overall further costs required for the provision of a supportive structure for the turbine, along with additional fine screening, a complex control system and a protective powerhouse would result in cost inefficiency that is unwanted. Finally, even if the flow conditions of the site are good, it must not be forgotten that the site is affected by the tide which would result in alternating heads and flows during specific times of the day, making the design of a low-head turbine a lot more difficult for that spot. This site could be a lot more suitable if a high head of more than 25 meters was available as it could be utilised by a Pelton, Turgo or Francis turbine intake.
22.1.3 Location 3 – Movable Weir Site 3 is the location for which the feasibility study of constructing a movable weir is undertaken. The site is located at the top of the estuary of River Medway and at approximately 4.3 km downstream of Allington. Assuming that the feasibility study for the weir goes through, the site will be consisting of a
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movable weir of approximately 60 meters in width and 1.4 meters in height when fully deployed. As already explained earlier in the report, the main purpose of the weir is to maintain the natural estuary flow downstream by impounding tidal water and releasing it at a controlled rate. The freshwater winter river flows are strong enough to keep the residual flow at an average level, whether during the summer the freshwater flows drop greatly. Therefore, the weir is mostly going to be operating during summer months as assistance will be required in maintaining the minimum residual flow of the estuary.
This site is considered to have both strong advantages and disadvantages. In terms of site accessibility, since the construction of the movable weir would require the provision of safe routes for material delivery, the same routes could be used for the delivery and installation of the turbine as well. Furthermore, as the turbine would most likely be installed on a non-mechanically operating part of the weir, close to the end-supports, the continuous inspection and maintenance of the turbine could be easily undertaken during low-tide. In terms of the ease of construction, this location is not as complex as Site 2. However, due to the involvement of heavy tidal flows and the fact that the weir is not constantly impounding water at a standard level of head, it would be quite difficult to produce a highly efficient design for this location as several uncertainty factors are introduced. Even if the costs of construction would not rise significantly, a turbine installed at this location would have to be very flexible to constant head and flow changes. Site 3 is hardly favourable when compared to Site 1 but since working with tidal water instead of freshwater would magnify the purpose of this study, the location will be assessed to prove so.
22.2 Hydro-power Machinery Options
When it comes to hydro-power generation, there are numerous types of turbines which come with different strong and weak elements depending on the conditions present at the targeted site. Between hydro-unit plants, all involve the function of some sort of gearbox which drives a generator but majorly differ in the way of converting the kinetic energy in water to electricity (Practical Action, 2001). All options will most likely require a coarse screen to provide protection against large objects and a means of setting the turbine out of operation.
This feasibility study is dealing with two sites where the flows and the heads present are relatively low and follow a quite variable distribution due to the involution of tidal waters. Taking into account the above statement, the machinery chosen to be studied is the ‘Archimedean Screw Generator’ for reasons that are going to be explained within this section. Many turbine schemes such as Pelton, Francis and Inclined Jet were eliminated in the pre-feasibility study where the general site conditions in River Medway were revealed. In the feasibility study, turbine schemes such as Siphon Propeller, Cross-flow,
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and Waterwheel were eliminated for reasons very close to these of eliminating the Propeller/Kaplan turbine. The following summaries are provided to give a comparison between the two schemes that are considered as the best suitable for the proposed sites.
22.2.1 Archimedean Screw Generator The ‘Archimedean Screw Generator’ is a modified reverse version of the classic ‘Archimedes Screw (Pump)’ which has been known as a pumping tool since antiquity. The ‘Archimedes Screw’ consists of a shaft axis with a blade helix attached onto it which is placed in a case of an open semi-circular or closed circular cross section inclined at a favourable angle to carry the flow (Muller & Senior, 2009). The turbine takes advantage of the energy difference between the water flowing through the intake of the screw at a high head level and the water flowing out of the screw at a low head level as the screw is turning and the generator is being driven by the resulting rotational motion (Walker & Moreno, 2009).
Figure 22-4: Representation of an Archimedean Screw Turbine (Kalkani & Stergiopoulou, 2013).
Advantages
The turbine is environmentally friendly as it enriches the water quality with dissolved oxygen,
reduces CO2 emissions, does not affect the already existing wildlife and captures the natural flow of the river without any alternations (Landustrie, 2012).
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The screw turbine is designed to be able to generate electricity at 24 hours throughout the whole year if desired or could be simply controlled by the installation of a constantly controlled inlet sluice gate (Landustrie, 2012). The screw operates at atmospheric pressure and slow rotational speeds (20-40 rpm), thus poses no risk of injury to fish as the water pressure remains constant and adequate space for passage between blades is available (Mann Power Consulting Services, 2008). While the screw is in operation, an adequate amount of flowing water is always going to be present within the screw’s blades, letting river debris pass through easily. As a result, the need for the installation of fine screening and frequent thrash screen maintenance is eradicated. The screw would only require the installation of a coarse screen to keep large pieces of debris and mammals from entering into the inlet, bringing initial and maintenance costs down (Mann Power Consulting Services, 2008). The efficiency and the operation of the screw is hardly affected by a variable upstream/downstream flow and head distribution (Walker & Moreno, 2009). The amount of civil works for the installation of an ‘Archimedean Screw Turbine’ are minimal as it only requires simple modifications to be done on already existing structures and the only excavation work required is for placing a concrete pad at the outlet (Glenn Hydro, 2011)
Disadvantages
An axial-flow Kaplan turbine would provide a much larger power output at a great efficiency, when operating at the design flow (Mann Power Consulting Services, 2008).
22.2.2 Propeller/Kaplan Turbine This specific type of low-head/high-flow turbine can be referred to as a ‘propeller’ or ‘axial-flow’ turbine. The turbine basically consists of a large vertically placed propeller with blades of variable pitch which alternate in angle depending on the volume and flow-rate of the incoming flow or the power demand changes in order to match an appropriate efficiency (Glenn Hydro, 2011). The mechanism of the turbine functions with flow reaction by allowing the water flow through axially while the propeller is reacting at up to a double rotational speed and obliges water to release its kinetic energy for harnessing (Addnew Hydropower Ltd., 2013).
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Figure 22-5: Representation of an axial-flow Kaplan Turbine (Renewables First, 2014).
Advantages
No other turbine scheme can match the efficiency of a Kaplan turbine when operating under optimal flow conditions (see Figure 6).
Disadvantages
The Kaplan turbine has higher initial costs in comparison with the rest of the listed options. The complex function of the turbine requires increased protection at the intake against river debris as it could easily damage the turbine’s runner. Therefore, the mechanism requires the installation of elaborate fine, fish and trash screening which would increase the overall capital and maintenance costs and decrease the effective head (Walker & Moreno, 2009).
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As the turbine lets water through the intake at the top and releases the flow at the lower end of the turbine, a good amount of civil works would be required in order to achieve effective channelling (Glenn Hydro, 2011). The efficiency of the turbine drops greatly when operating at lower flows than the design flow in comparison with the Archimedean Screw Generator (Mann Power Consulting Services, 2008). Where the flow follows a variable flow distribution, the turbine requires a complex control system for its continuous effective operation (Mann Power Consulting Services, 2008).
22.2.3 Efficiency Comparison As the proposed sites are more or less affected by a variable flow distribution, it is very important to look at how the efficiency of the selected turbine changes when the flow is alternating from the design flow. This is because turbine efficiency is one of the most significant parameters in the resulting electricity generated and the associated revenue.
The graph below shows how the theoretical efficiency changes with a decreasing flow, by turbine type.
Figure 22-6: Efficiency change against increasing flow by turbine type (Mann Power Consulting Services, 2008).
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As it can be seen from the graph, an Archimedean screw is theoretically able to operate quite efficiently, from a maximum design flow and a maximum efficiency of ≈ 85% to even down to 15% of the maximum design flow. In opposition, the propeller turbine can be seen to react clumsily when the available flow passes the 90% mark of the design flow and stops being any efficient by the 60% mark.
As the project asks for a relatively cost-effective, environmentally friendly and independently regulating solution, the ‘Archimedean Screw Generator’ can be considered as the most suitable solution.
22.3 Installation and Conceptual Layout
The placement location and the components of an ‘Archimedean Screw Generator’ scheme need to be selected carefully in order to minimise the installation and whole life costs and maximize the design life and protection of the ecosystem. The main plan for the two locations is to construct a simple intake structure within the weir’s width which would direct the flow through the inlet channel and the screw turbine to be released at the bottom of the outlet. As far as it is known, fish passage will not be a significant problem at the two sites since sluice fish passage is provided at Allington lock and spillway and the migration of fish at the movable weir is deemed possible with the tidal conditions as discussed in previous chapters (Environment Agency, 2012). To note, the issues discussed in the following paragraphs of the section will need to be studied in detail after the feasibility study.
22.3.1 Screw and Supportive Structure In both cases, the Archimedean screw would be positioned adjacently to the weir and would be placed on the left side of the structure. The screw is designed to be installed at 22o from the horizontal of the downstream river bed since this angle is considered to be the most appropriate angle for an efficient operation (Rorres, 2000). Depending on the diameter of the turbine 1.4m, a concrete trough of 1.5-4.5 meters width would be constructed within the width of the weir in order to accommodate a cast-in steel case produced for half the diameter of the screw in height, which would remain as a support inside the concrete. The outlet of the screw is designed as obstacle free and would be situated as close as possible to the downstream bed of the river for the minimisation of excavation civil works.
For Allington Weir, depending on the sizing of the screw, a part of the sluice gate of the weir would need to be cut out and set out of operation in order to prepare it for being used solitarily for the screw.
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For the movable weir, depending on the diameter of the screw, the original design plans of the weir would have to provide adequate stationary space alongside the weir’s supports on which the turbine inlet would be able to be installed.
22.3.2 Intake Structure By carrying out the modifications stated above, sites would be ready for the construction of an intake structure to the turbine. In both sites, the inlet channel of incoming flow to the turbine would be formed by a concrete intake structure. The structure’s designs consist of a short span concrete millstream of 1.5-4.5 (depending on the diameter of the screw) and 1.5-8 (1.5 for moveable weir, 8 for Allington weir) meters width and depth respectively, which will be leading to an inclined coarse screen with a maximum vertical bar spacing of 150mm and a width of up to 4 meters which allows safe passage to all fish species present in the river. The limits mentioned are the maximum limits suggested for the protection of the screw (HUBERT , 2014). An automated stainless steel sluice gate would be installed just downstream of the coarse screen and would be controlling the flow into the turbine by maintaining the residual flow and shutting down the operation in cases of flooding risk and maintenance procedures. A concrete Π-shaped structure would be constructed from the edge of the supports to the end of the concrete intake in order to support the system’s components and the powerhouse of 5x5 m2 at maximum for the accommodation of the generator and the gearbox. It must be ensured that the powerhouse is made by a water resistant material and that access is not allowed to unauthorized persons for safety purposes.
For Allington Weir, the intake of the turbine has been designed to be placed at 4.65 meters height from the river bed downstream and has been estimated to suffer a loss of approximately 15 mm of head due to the friction forces acting between the coarse screen and the flow.
For the moveable weir, calculations for annual power generation were carried out for three different heights for the placement of the turbine’s intake and it was estimated that installing the intake at 1.2 meters would provide the most efficient result. The head friction losses are taken as 15mm for this case as well, but the final value will be clearly dependent on the actual dimensions and shapes of the structures. Furthermore, a completely secure water resistant powerhouse would be required in order to protect the mechanism accommodated. This is one of the reasons why the design of an ‘Archimedean Screw Generator’ at the moveable weir is very complex and probably not feasible.
An example general arrangement for a scheme at Allington is provided in the Appendix for further clarity.
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22.3.3 Generator Mechanism The generator mechanisms were chosen to be three-phase asynchronous generators mainly because they are not negatively affected by the turbine under or over-operating (H2OPE Water Power Enterprises, 2008). More specific generator models were chosen by looking at the factored maximum theoretical power output that the scheme can give. All generators were selected from a 400 V, 50cps (Hz) design point. This type of generator is considered as a three-phase asynchronous generator with squirrel-cage rotor, series G11R, with surface ventilation, Mode of operation S1, continuous mode of operation, insulation class F, degree of protection IP55 (VEM Motors GmbH, 2011).
Table 22-1 Generator Mechanism Sizing Options
Allington Weir Location Movable Weir Location
Sizing Option 1: D=1 G11R 180 M4 1500RPM 4Pole G11R 132 M4 1000RPM 6Pole
Sizing Option 2: D=2 G11R 225 M6 1000RPM 6Pole G11R 160 M6 1000RPM 6Pole
Sizing Option 3: D=4 G11R 250 M4 1500RPM 4Pole G11R 180 L6 1000RPM 6Pole
22.3.4 Control System The screw as a turbine is connected to the generator through a gearbox and hence, a control system is required for the control of the related operation of the three and the flow approaching the scheme. The control system chosen is a standard computer automated control system which is able to control the water flow and head in the inlet channel by adjusting the portion of the height of the sluice gate. That is in contact with flowing water. Furthermore, the control system is able to synchronise the turbine for the flow present at an instantaneous time through data logging/transmission. The power output is estimated for a fixed speed control system, however a variable speed control system might be more suitable for the situation of the proposed sites and is something that should be studied in later stages (H2OPE Water Power Enterprises, 2008). Through the control system, the scheme will be able to be shut off in situations of potential flood risk and maintenance. Finally, at times where the available flow utilised by the generator is less than 15% of the design flow, the turbine will be set out of operation in order to maintain an aesthetic river environment and let the natural flow be.
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22.4 Hydrology Assessment
The ‘Hydrology Assessment’ and ‘Conceptual Design’ sections are considered as the most significant sections of the report as they present the actual expected site conditions and the optimum responsive designs for each site.
Run-of-river hydro-power schemes are used to generate electricity by harnessing the kinetic energy in falling water and converting it to power. In theory, the amount of energy that can be harnessed by a sized hydro-unit can be estimated as proportional to the height from which the water falls and the volume of water involved on site (Perth & Kincross Council, 2014). In order to be able to get an accurate estimate of the potential power output, long-term head and flow data need be provided. This section presents ‘Flow Duration’ and ‘Head Duration Curves’ which can be then used for sizing the unit and determine a value for the mean annual power generation.
The flows that were initially used were obtained from the flow gauging station at Allington Weir for a period of 10 years from 2003 to 2013. Then, as the river model was being developed, data such as that of river depths and tidal flows were used in order to get good estimates for the flow-rates and heads at the location of the movable weir and the heads at Allington.
22.4.1 Location: Allington Weir Flow data provided by the river model, after future abstraction has started taking place, was used to develop the following ‘Flow Duration Curve’ for the location of Allington Weir. Throughout the UK, this curve is considered as the essential means for providing a summary of the hydro-characteristics of a river and can be further used for setting out abstraction limits and license conditions in concern with the river flow (Copestake & Young, 2008).
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Figure 22-7: Flow Duration Curve for Allington Weir.
The ‘Flow Duration Curve’ was used to break down the derived flow-rates at Allington Weir into a series of flow-rate ranges, in 5% exceedance probability steps which basically represent the probability of flows matching an expected value throughout a full year of operation. Therefore, Q50 = 5.06 m3/s suggests that for 50% of the year it is expected that a flow of 5.06 m3/s is going to be matched on site. The British Hydrological Society, suggests that Q95 = 2.11 m3/s of the total river flow should be taken as the minimum residual flow (British Hydrological Society, 2004). As the minimum residual flow must be let free by the hydro-unit, the curve was modified to present the available flow in the river as well. Even if the actual M.R.F. of the river is known for the location of the movable weir, it is safer to set Q95 and confirm the exact value with the Environmental Agency at a later stage, rather than converting to obtain an uncertain value for Allington.
By looking at the graph, it can be seen that the first 30% of expected flows follow a quite variable distribution even if the flow regime upstream is not affected by tidal waters. As this location is the starting location and upstream of the location of the movable weir, it is expected that with the inclusion of tidal conditions the other site is going to follow an even more variable flow distribution.
In terms of available river height, the site can provide up to a maximum net head of 3.46 meters down to a minimum head of 2.89 meters throughout a day. To clarify, these are heads measured at 24 hour intervals for the purpose of summarising the river’s characteristics. At specific times where the tide is
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out and the present flow is minimal the net head can reach up to 4.60 meters and where the tide is in and the flow is maximum the net head can reach down to 0.13 meters.
Figure 22-8: Head Duration Curve for Allington Weir.
22.4.2 Location: Movable Weir For the purpose of estimating expected flows and heads for this location, it is assumed that the weir is only going to extensively operate during summer months while freshwater flows are noticeably reduced and assistance is going to be required by tidal water for maintaining the natural estuary flow. Therefore, the analysis of the characteristics of this site is divided into two parts, the winter analysis (September to May) and the summer analysis (June to August).
22.4.2.1 Winter Analysis The analysis of the winter months consists of data for 272 days, from the 1st of September to the 30th of May.
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Figure: Flow Duration Curve for the movable weir during winter.
For 50% of the winter period, it was found that a mean flow Q50 = 3.20 m3/s is going to be matched on site over 60 meters of width. The actual value of residual flow to be maintained at this location is known to be 2.083 m3/s, hence the available flow is less by 2.083 m3/s. As it can be seen from the graph, due to the tidal conditions and the variable distribution of the flow, there is only going to be availability for utilisation for approximately 55% of the time. This means that the maximum potential time of operation is immediately dropped by 45% when it only is 6% for Allington.
During the winter period, the movable weir is not going to be used actively which means that no significant volume of water is going to be impounded at the location and water is not going to be able to reach the intake of the turbine at all times as it is going to be installed at a specific height. Therefore, by installing a turbine with an intake at 1.2 meters, it would only be in operation at high levels of water (>= 1.2 m) and low head efficiencies and automatically be out of operation when the water depth is not enough to reach the intake (<1.2m). As a conventional head duration curve cannot be provided for this case, a graph showing the average winter water levels is provided.
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Figure 22-9: Water Level Duration Curve for the movable weir during winter.
By putting the water levels at the location of the movable weir in a descending order and setting the intake height at 1.2 meters, it was identified that when the weir is not deployed, the water depth level is expected to reach the intake of the turbine 65% of the time throughout an average winter period. 1.4.2.2 Summer Analysis
The analysis of the summer months consists of data for 93 days, from the 30nth of May to the 31st of August.
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Figure 22-10: Flow Duration Curve for the movable weir during summer.
The graph presents daily average flows at the movable weir during the summer period. As it can be seen, the average daily flow is governed by tidal waters. By studying the positive downstream travelling flows at the location in 6 hour time-steps, it was identified that an installed turbine would only be able to operate for 11 days out of 93 of the summer period. The mean daily flow for the period is negative and the available flow to the turbine ceases at the top 5%.
During the summer, where the movable weir is used extensively, a means of impoundment before the intake is introduced and a conventional head difference can be seen much more clearly. The heads shown below are heads for water at the top of the weir when deployed, to the water level below the weir.
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Figure 22-11: Head Duration Curve for the movable weir during summer.
By relating the results obtained from the flow and head duration curves, it can be seen that the amount of power generated would be insignificant and it would be better off setting the turbine out of operation throughout the summer in order to let the weir solely deploy.
22.5 Conceptual Design
In this section, river data provided in the ‘Hydrology Assessment’ are converted to match differently sized systems. For each of the proposed sites, three sizing options are presented in order to identify how different screw diameters and design flows can affect the resulting annual power generation and revenue gained. ‘Flow/Head Duration Curves’ and ‘Power Output Duration Curves’ are provided for each option while details such as their up-time and running efficiencies are mentioned. In the end of the section, it will be clear which designs are the optimum for each site and which site is the most favourable for hydro-installation.
22.5.1 Options Explained By alternating the design diameter of an ‘Archimedean Screw’, the power output, efficiency and resulting cost/benefit ratio of the hydro-scheme change noticeably. This is mainly because the amount of flow utilised by the generator of the scheme alternates proportionally. The sizing options are explained below and power outputs and cost/benefit estimates are then presented.
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22.5.1.1 Sizing Option 1 The proposed sites, ‘Allington Weir Location’ and ‘Moveable Weir Location’ are assessed for the installation of one Archimedean screw of a diameter of 1 meter that is able of utilising a generator design flow of 0.38 m3/s and 0.40 m3/s at overall efficiencies of 64% and 22% respectively.
22.5.1.2 Sizing Option 2 The proposed sites, ‘Allington Weir Location’ and ‘Moveable Weir Location’ are assessed for the installation of one Archimedean screw of a diameter of 2 meters that is able of utilising a generator design flow of 0.63 m3/s and 0.66 m3/s at overall efficiencies of 66% and 16% respectively.
22.5.1.3 Sizing Option 3 The proposed sites, ‘Allington Weir Location’ and ‘Moveable Weir Location’ are assessed for the installation of one Archimedean screw of a diameter of 4 meters that is able of utilising a generator design flow of 1.14 m3/s and 1.19 m3/s at overall efficiencies of 60% and 13% respectively.
22.5.2 Allington Weir Location – Sizing Options Assessment The flow/head duration curve below presents the flow-rates and heads that the turbine’s generator would be able to utilise for renewable electricity generation throughout an expected average year. The maximum flow reached by each different generator is the design flow of Q50 set for each sized turbine. In order to reach these numbers, the site flows presented in the ‘Hydrology Assessment’, were converted to the flows expected to be obtained in the area potentially covered by a hydro-unit and then were converted to flows that would be utilised by the installation of a scheme at that spot. With the changes expected to be identified as explained before, it reach higher accommodated flows within the screw as its diameter increases.
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Figure 22-12: Flow/head duration curve for the comparison of flows for different sizing options.
With the changes expected to be identified as explained before, it can be seen that higher accommodated flows are reached within the screw as its diameter increases. As the net head available at the side follows a smoothly alternating distribution, the power output and energy captured by the unit presented in the graph below, can be seen to be proportional to the flow available for utilisation. The power outputs presented are the power outputs resulting after the involvement of the turbines, gearboxes, generators and cable transmission efficiencies.
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Figure 22-13: Energy capture duration curve for different sizing options.
22.5.3 Movable Weir Location – Sizing Option Assessment 22.5.3.1 Winter Analysis As it can be seen from the graph below, even if the schemes have been designed in order to be able to capture almost equal flows at 100% capacity, a scheme potentially installed at the location of the movable weir would not be able to operate at its maximum capacity for more than 15% of the total winter period and would furthermore not be able to operate at all during 45% of the winter period and the whole of the summer period.
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Figure 22-14: Flow/head duration curve for the comparison of flows for different sizing options.
Hence, the resulting values for the energy capture and power output, which are presented below, can be seen to be quite poor
Figure 22-15: Energy capture duration curve for different sizing options.
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22.5.4 Summary Tables of Options In this sub-section, the annual power generation and carbon savings of each scheme are presented.
22.5.4.1 Allington Weir Location
3 Diameter (m) Design Flow (m /s) Max Power Output (kW) Option 1 1 0.38 17.30 Option 2 2 0.63 28.83 Option 3 4 1.14 51.89 Operating Efficiency (η) Annual Power Generation (kWh) Carbon Saved (t) Option 1 64% 53124.49 26.04 Option 2 66% 102449.70 50.25 Option 3 60% 183989.44 90.20
The excel sheets used for the estimation of the annual power generation for the schemes at Allington can be found in the Appendix for further clarity.
22.5.4.2 Moveable Weir Location
Diameter (m) Design Flow (m3/s) Max Power Output (kW) Option 1 1 0.40 4.70 Option 2 2 0.66 7.80 Option 3 4 1.19 14.00 Operating Efficiency (η) Annual Power Generation (kWh) Carbon Saved (t) Option 1 22% 3712.05 1.82 Option 2 16% 5966.16 2.92 Option 3 13% 9442.00 4.63
An example excel sheet for the estimation of the annual power generation for a scheme at the moveable weir can be found in the Appendix for further clarity.
22.6 Grid Connection
As briefly mentioned before, the electricity generated is meant to be sold directly to the grid with the aim to contribute to the reduction of emissions and costs sourced from pumping. In order to do so, a complete supply system is required. The system would consist of a three-phase transmission cable spanning from the hydro-unit to the nearest sub-station plus required metering and protective components.
22.6.1 Allington Weir Scheme As the generating capacity of the Option 1 and 2 hydro-schemes for the ‘Allington Weir Location’ falls under the category of 50kW or less for a three-phase grid connection connected at 400V, the project
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will need to follow the EREC G59 standard for simple installations (Energy Networks Association, 2014). Option 3 hydro-scheme would still follow the EREC G59 but different requirements would be asked by the DNO for its installation. The chosen scheme would be connected to the Maidstone 133/33 KV grid sub-station (TQ76855585), approximately 2.8 km South-East of Allington, with a 33 KV U/G cable (UK Power Networks, 2012). The cable’s transmission losses are taken as 1% for allowance. The costs of this connection would consist of the civil works required for connecting the cable between the generator and the sub-station, the connection with a three-phase transformer, a simple control system and an export meter.
22.6.2 Movable Weir Scheme The generating capacity of the hydro-schemes for the ‘Movable Weir Location’ falls under the category of 11.04kW or less for a three-phase grid connection connected at 400V. Therefore, the project can follow the EREC G83 standard single premises with standard settings and not required by the District Network Operator (DNO) (Energy Networks Association, 2014). The scheme chosen would be connected to the Burham 33 KV grid sub-station (TQ71716014), at 580 meters North-West of the location of the movable weir, with a 33 KV U/G cable (UK Power Networks, 2012). The cable’s transmission losses are taken as 1% for allowance. The costs of this connection consist of the same as the costs of the Allington Weir Scheme, however would be much less costly in total due to the difference in power output and distance to the sub-station.
22.7 Cost and Benefit Estimation
In this section, the capital and annual operation costs of the schemes are weighted against the annual revenue potentially obtained. Furthermore, the differences between different sizing options are presented in order to identify which option would most likely be the governing in terms of cost/benefit and overall efficiency. It is believed that by now, it is pretty much clear that installing a small-scale hydro-power plant at the location of the movable weir would not be worth it as the potential power output capacity is incredibly low when compared to the respective schemes for the location of Allington. Therefore, the schemes for the movable weir location are not going to be included in this section.
22.7.1 Income & Revenue
By installing a small scale hydro-plant and generating renewable and CO2 saving electricity, the system is eligible for the UK Government’s Feed-in-Tariff scheme (FIT) (Energy Saving Trust, 2014). The income paid for exporting electricity to the grid is made up by the following:
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Table 22-2: Tariff Rates for Hydroelectricity (Energy Saving Trust, 2014).
Plant Technology Tariff Band (kW) Tariff Type Rates (p/kWh)
Hydro >15 - <100 Export 4.77
Hydro >15 - <100 Generation 17.75
The rates quoted in the table are correct for until the 31st March 2015 when new rates are going to be published with no major changes most likely. For a small-scale hydro-plant like such shown in this feasibility study, the accreditation process needed is the ROO-FIT which is much simpler than MCS. The tariff is going to be applying for the 20 first years in the case of hydro generation (Energy Saving Trust, 2014). The total revenue obtained per annum is estimated by subtracting the ongoing costs from the income and is presented later.
22.7.2 Cost/Benefit Analysis Summary Most of the quotations obtained are from feasibility study reports that MannPower Consulting Ltd., one of the most well-known companies in ‘Archimedean Screw Generator’ installations, has published for clients.
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Cost/Benefit Analysis Location: Allington Option 1 Option 2 Option 3
19 January 2015 Diameter = 1m Diameter = 2m Diameter = 4m
Specifications
Design Flow (m3/s) 0.38 0.63 1.14 Maximum Power Output (kW) 17.30 28.83 51.89 Maximum Efficiency 64.00% 66.00% 60.00% Number of Screws 1 1 1
Capital Costs
Technical Design MannPower Quote £3,500.00 £3,500.00 £3,500.00 Project Plan 2% Budget Quote £2,465.60 £3,307.10 £4,840.34 Relevant Application Fees Published Rates £755.00 £755.00 £755.00 Coarse Screen MannPower Quote £1,170.00 £1,950.00 £3,510.00 Sluice Gate MannPower Quote £6,685.71 £11,142.86 £20,057.14 Archimedes Screw MannPower Quote £15,977.29 £31,954.59 £63,909.18 Generator VEM Motors Quote £6,250.00 £8,534.00 £12,270.00 Control/Grid System Rough Estimate £6,000.00 £6,000.00 £6,000.00 Transportation MannPower Estimate £3,600.00 £3,600.00 £3,600.00 Craneage MannPower Estimate £2,400.00 £2,400.00 £2,400.00 Supporting Structure MannPower Quote £11,619.85 £23,239.70 £46,479.40 Civil Works to Channels MannPower Quote £16,125.00 £28,828.13 £47,578.13 Powerhouse MannPower Estimate £6,000.00 £6,000.00 £6,000.00 Grid Connection Estimate £35,000.00 £35,000.00 £35,000.00 Civil Works to Cable Estimate £15,000.00 £15,000.00 £15,000.00 Project Management 5% Budget Quote £6,287.25 £8,433.10 £12,342.85 Installation 3% Budget Quote £3,960.96 £5,312.85 £7,776.00 Total Installation Costs £142,796.67 £194,957.32 £291,018.03 Costs per kW £8,254.14 £6,762.31 £5,608.36
Annual Costs
Operation MannPower Estimate £225.00 £363.00 £650.00 Insurance MannPower Estimate £639.00 £914.00 £1,441.00 Meter Reading Standard Fee £300.00 £300.00 £300.00 Maintenance MannPower Estimate £1,100.00 £1,860.00 £2,480.00 Total Annual Costs £2,264.00 £3,437.00 £4,871.00
Annual Income
Power Output (kWh) Modelled Data Calculation 53124.49 102449.70 183989.44 CO2 Savings (t) 0.490 tonnes per MWh (DEFRA) 26.04 50.22 90.20 Efficiency Result 62.00% 63.00% 57.00% Electricity Export Sales Current Rates £2,534.04 £4,886.85 £8,776.30 Feed In Tarrif Current Rates £9,429.60 £18,184.82 £32,658.13 Total Annual Revenue £11,963.64 £23,071.67 £41,434.42 Total Annual Income £9,699.64 £19,634.67 £36,563.42 Payback in Years 14.72 9.93 7.96 Return on Investment 0.07 0.10 0.13
22.7.3 Conclusion As it can be seen from the analysis, the ‘Archimedean Screw Generator’ is able to provide a quite proportional power output with changing diameters. It is believed that a well maintained screw turbine can reach up to a design life of 40 years with a complete overhaul every 15 years (Stockton, 2014). As the site’s flow conditions will be changing with time, it is expected that the turbine is still going to be able to operate efficiently but it is probable that the actual annual power generation of the scheme will
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start falling along. By comparing the results obtained with similar studied projects of companies such as Landustrie Sneek BV (Landy Hydropower Screws) and Mannpower Consulting Ltd., it is identified that Options 2 and 3 for Allington can be deemed feasible. Option 2 can be considered as the most favourable choice for the location as it will theoretically be able to operate at the highest overall efficiency of 66% and generate a respected amount of electricity throughout an expected average year. Depending on the tolerance to increased capital costs, it would be further advised to consider Option 3 as even if it offers a lower overall efficiency, it is able to provide the highest return on investment and annual power output.
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Construction Phasing
Normally the ideal time to carry out engineering works in a river would be during the summer as this when the flow is at its lowest. However this is often the time when adverse environmental impact is likely to be the greatest and when the river is being used the most by recreational users. For the minimum impact to the local fish construction in the autumn and winter is likely the best option therefore a compromise is needed. It is recommended in the River Weirs – Good Practice Guide (Rickard, et al., 2003) that the construction should avoid or mitigate against the following seasonal activities:
Fish migration and spawning Bird and mammal breeding Angling (especially organised competitions or events) Navigation and boating (in particular Easter to Autumn)
23.1 Site Access
Figure 23-1: Site Access
As can be seen in Figure 23-1the proposed location for the weir can be accessed by roads which run alongside the river bank.
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3
2 1
Figure 23-2: Current Site Users
The current users of the land bordering the site according to what can be seen using Figure 23-2 appear to be a scrap heap on the western bank (location 1) and a solar farm bordering the eastern river bank (location 2). There also appears to be a project currently under construction north of the scrap heap (location 3).
The companies responsible for running each of these facilities will need to be contacted to determine the viability of using part of their site for construction works. The ease of accessing the site will also need to be determined to see if there are any restrictions such as tight bends or narrow roads that would prevent certain plant from accessing the site. This ease of access will determine if any adjustments to the design need to be made.
Once access has been determined and agreed enabling works such as tree pruning and footpath closures can be organised in advance of the start of works.
23.2 Temporary Works
Temporary works will very likely be required for the construction of the weir. There are various types of temporary works that can be used to ensure the works area is isolated from the river water. The
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recommended types of temporary isolation can be found using Figure 23-3, which stated that due to the fact that the works can be phased it would be best to use a coffer dam.
Figure 23-3: Choosing a method for isolating a works area in rivers (Scottish Environment Protection Agency, 2009)
23.3 Cofferdam Construction
To allow for the construction of the movable weir a cofferdam will need to be constructed. This cofferdam would be best constructed from marine barges as can be seen in Figure 23-4 as this allows for minimal disturbance to the riverbed while at the same time providing a safe a secure works area.
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Figure 23-4: Cofferdam installation from marine barges (The Mersey Gateway, 2014)
There will likely need to be a minimum of three phases of construction to minimise disturbance and thus three cofferdams will need to be installed. The minimum three phases would be western bank, eastern bank and central section. During the western and eastern bank construction period the river will be still accessible and so this works can happen over summer. For the central section this can be done using one cassion, however this would block off the river to all users and fish, therefore this may need to be phased so that there are 2 or more cassions may be required however this would depend on the river profile and whether the river users (e.g. boats) are able to make it around the cassions. See Figure 23-5 and Figure 23-6 below for details.
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Figure 23-5: Partial river isolation/ cofferdam (Scottish Environment Protection Agency, 2009)
Figure 23-6: Partial isolation using a caisson (Scottish Environment Protection Agency, 2009)
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23.4 Construction Gantt chart
Figure 23-7 Construction Phasing
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Financial Analysis
For this Tidal water project, with the installation of a movable weir in the River Medway two types of appraisal methods can be investigated to give a view as to whether the project is financially beneficial to the stakeholders, in the case the water companies, the government and the water customer in the South East region of the UK.
24.1 Appraisal Method 1
One of the appraisal methods that can be applied to the addition of a movable weir in the River Medway is a comparison of the Net present value (NPV) of cash flows with new technology (the movable weir) and without the new technology over the life of the investment. This investment solution will be sensitive to the future cost of carbon, capital costs and the effectiveness of different measures proposed to solution the problem of water supply and the saving energy and carbon usage.
24.1.1 Projection of Future cash flows The cash flow for the project as it currently stands is as follows:
The life of the weir 75 years Maintenance costs – sedimentation removal and remedial repairs (£/year) 500 Maintenance costs – every 10 years major repairs (£/10 years) 2,000 Energy saved per year from pumping (£M/year) 0.5 Price of electricity (£/kWh, year 1) 0.1 Real increase in electricity price (%) 3% Annual rate of inflation (%) 2% Maximum amount of energy that can be produced (kWh) 178,414
Table 24-1: Capital costs of the project
Year Year 1 Year 2 Year 3 Year 4 Notes 10
Design Work, Environmental
Assessment and £0.5M mitigation proposals arising from the assessment, Permits,
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and miscellaneous items.
Design, permits, work Moving of abstraction force, equipment, civil £0.75M point works and mitigation that is required
Civil works, erection, commissioning, Installation of the hydro £300,000 safety, Materials, unit and generator work force and site set-up and equipment
Civil works, erection, commissioning, Installation of movable £1.5M safety, Materials, weir work force and site set-up and equipment.
Running cost of the Operation, insurance £2,500 £2,500 £2,500 hydro unit and meter reading
Signs for and around Safety installations £10,000 the weir and the hydro unit
Removing Maintenance for hydro sedimentation and £3,500 £3,500 £6,000 unit and weir repairing any damages and wear and tear.
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Total Capital Cost £1.25M £1.801M £4,000 £4,000 £8,500
NOTE: All figures used above have been rounded up to assume worst case scenario. Year 10 represents a year where maintenance is required off the weir and hydro unit.
Table 24-2: Energy saving cost
Year 1 Year 2 Year 3 Year 4 Year 5 Year 10
Pumping £0.5M £0.525M £0.552M £0.58M £0.742M
Hydro unit £0.04M £0.041M £0.041M £0.042M £0.045M
Table 3: Cash Flow – comparison of the price for the water companies with and without the weir and hydro unit
Year 1 2 3 4 5 10 25 50 75 Without the weir Cost of £0.525 £0.552 £0.58 £0.742 £1.612 £5.460 £18.49 £0.5M electricity M M M M M M 1M With the weir £1.25 £1.801 Capital cost M M Maintenance £4,000 £4,000 £4,000 £8,500 £8,500 £8,500 £8,500 cost Cost of £0.54 £0.566 £0.593 £0.622 £0.787 £1.621 £5.469 £18.5 electricity M M M M M M M M profit Total cost Additional
Cash flow £1.25 £1.261 £0.562 £0.589 £0.618 £0.779 £1.613 from weir £5.461 £18.49 M M M M M M M and Hydro M M
unit NOTE: A more in depth study of the options and the amount of energy that can be captured by each option and the time it would take can be found in the hydro unit section.
Table 4: NPV of cash flow
Year 1 2 3 4 5 6 7 8 9 10 Cash flow -£1.25 -£1.26 £0.56 £0.59 £0.62 £0.65 £0.67 £0.70 £0.73 £0.78 (M) Discount Factor 1.000 1.115 1.243 1.386 1.546 1.723 1.922 2.143 2.389 2.664 Discounted Cash -£1.25 -£1.13 £0.45 £0.42 £0.40 £0.37 £0.35 £0.33 £0.31 £0.29 Flows (M)
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NPV (M) -£1.25 -£2.38 -£1.93 -£1.50 -£1.10 -£0.73 -£0.38 -£0.05 £0.25 £0.55
Year 25 50 75 Cash flow £1.61M £5.46M £18.49M Discount Factor 13.633 207.238 3150.215 Discounted Cash £0.12M £0.03M £0.01M Flows
As can be seen from above with the addition of the installation of the movable weir in the River Medway the stake holders, namely the water companies, can save money. As this project is sensitive to the price of electricity and the effectiveness of other solutions it can be seen as a risk to the water companies to invest in the movable weir and the hydro unit. After 10 years, it is difficult to appraise the economic value of this project as prices of electricity cannot be estimated for the entire project. Furthermore, as appraisal method 2 will show it is highly dependent on the environment and external conditions being favourable.
24.2 Appraisal Method 2
The second appraisal method is that of the comparison of the NPV of the cash flows from alternative solutions (as shown in the group section under other schemes there NPV values ca be shown here too). Here each of the solutions proposed will be tested against external scenarios and the solutions will be ranked as to the others which are the most viable under those conditions. At the end the proposed solution which is most viable in all scenarios will be the most viable option to the current problem.
The external scenarios that will be evaluated are as follows:
Increase or decrease in rain fall Improvement in the cost of water technologies The cost of electricity does not increase The price at which electricity is sold at decreases or increases The solutions will be ranked as followed:
1. Large improvement in the risk and possible savings of the project 2. Improvement in the risk and possible savings of the project 3. Not affected by the external scenario 4. Slightly affected by the external scenario 5. Majorly affected by the external scenario
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24.2.1 Rainfall 24.2.1.1 Increase in rainfall Proposal Ranking Weir and Hydro unit 1 Desalination 3 Leakage reduction 3 Reservoir raising 2 Water reuse 3 Development of existing groundwater sources 4 River Medway abstraction licence 5
24.2.1.2 Decrease in rainfall Proposal Ranking Weir and Hydro unit 5 Desalination 3 Leakage reduction 3 Reservoir raising 5 Water reuse 3 Development of existing groundwater sources 5 River Medway abstraction licence 5
24.2.2 Electricity 24.2.2.1 Price of electricity does not increase Proposal Ranking Weir and Hydro unit 4 – the savings costs would no longer out way the cost of construction Desalination 2 Leakage reduction 2 Reservoir raising 3 Water reuse 2 Development of existing groundwater sources 3 River Medway licence 3
24.2.2.2 The price of selling electricity increases Proposal Ranking Weir and Hydro unit 1 – the savings from no longer pumping would be greater Desalination 3
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Leakage reduction 3 Reservoir raising 3 Water reuse 3 Development of existing groundwater sources 3 River Medway licence 3
24.2.2.3 The price of selling electricity decreases Proposal Ranking Weir and Hydro unit 5 Desalination 3 Leakage reduction 3 Reservoir raising 3 Water reuse 3 Development of existing groundwater sources 3 River Medway licence 3
24.2.3 Improvement of water technologies Proposal Ranking Weir and Hydro unit 4 Desalination 1 Leakage reduction 3 Reservoir raising 3 Water reuse 1 Development of existing groundwater sources 3 River Medway licence 3
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Risk Assessment 25.1 Likelihood and consequence descriptors for risk assessments
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25.2 Risk Register Matrix
Objective of the risk assessment. RISK ASSESSMENT - RESIDUAL ACTION PLAN - RESIDUAL RISK IDENTIFICATION & MITIGATION RISK RISK Completed Potential Problty Impact RISK ACTION Ref Category Risk Mitigation (to Score ACTION PLAN Impact (1-5) (1-5) RATING OWNER Date) Extra Concrete stresses in Settlement foundation 1 Construction elements if 2 4 8 MEDIUM of Banks designed to limit floats are not settlement level Construction cannot be Boats in way Signage to warn carried out if 2 Construction of 3 2 6 MEDIUM boats of access Designer boats are in construction times the way of the site Severe delays to Materials not schedule as Ensure suppliers 3 Construction arriving on work can only 1 3 3 LOW know of time Contractor time be carried out restrictions during low tide The design would need to The scheme has change if the Changes to been future 4 Design specifications 1 4 4 LOW Brief proofed to some are altered, degree. for example if more water
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needed to be stored
The weir itself The scheme does not use any Failure to does not energy and there 5 Design reduce meet the 1 4 4 LOW is possibility of carbon clients the inclusion of a requirements hydro unit The scheme would not go ahead if 6 Design Competition another 1 5 5 LOW scheme was deemed more feasible The scheme River model does not The model has 7 Design deemed meet the been completed 3 2 6 MEDIUM invalid clients to guidance requirements The scheme Emphasise the Planning 8 External Funding cannot go 1 5 5 LOW importance of Committee ahead such a scheme The scheme Emphasise the Planning 9 External Political risk cannot go 1 5 5 LOW importance of Committee ahead such a scheme The scheme Not meeting The scheme Emphasise the complies with Planning 10 External planning cannot go 1 5 5 LOW importance of planning Committee regulations ahead such a scheme regulations
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The scheme has Effect on been future 12 External Climate amount of 2 4 8 MEDIUM proofed to some water needed degree. The Scheme Failure to would not be 13 Handover meet 1 4 4 LOW deemed fit for requirement purpose Cleaning The weir may ensure thorough 14 Operation Strategy not become 1 3 3 LOW maintenance acceptable inoperable plan Maintenance The weir may ensure thorough 15 Operation strategy not become 1 3 3 LOW maintenance acceptable inoperable plan The weir has an The weir override so it can Maintenance could be 16 Operation be accessed 1 3 3 LOW access dangerous to safely during low maintain tide The weir Security could be 17 Operation during damaged and 1 2 2 LOW operation become inoperable The weir Boats could be Signage to warn 18 Operation colliding with damaged and 2 3 6 MEDIUM boats of access Designer weir become times inoperable The boats Boats not Signage to warn would 19 Operation vacating 3 2 6 MEDIUM boats of access Designer become stuck area in time times in the area
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between Allington weir and the new weir The scheme Failure to does not 20 Operation reduce meet the 1 4 4 LOW carbon clients requirements The weir would 21 Operation Tidal Surge experience 1 5 5 LOW hazardous forces The floats are mounted on springs so that The weir the weir only would operates under 22 Operation Bow Waves experience 1 4 4 LOW tidal movement hazardous and are also in a forces housing to protect from wave action Risk to Salinity environmental 23 Operation levels and 2 3 6 MEDIUM increase ecological area Public Risk of falling, Signage to attempting 24 Operation drowning or 2 4 8 MEDIUM explain risks to to walk injury public across weir
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The weir Maintenance could be schedule to 25 Operation Corrosion damaged and 4 2 8 MEDIUM check on become condition of weir inoperable The weir Maintenance could be Clean the build- schedule to 26 Operation Silt Build-up damaged and 4 3 12 HIGH up when check on become necessary condition of weir inoperable
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Appendix A Finance
Calculation Result Concrete Volume of concrete: Columns: 7 × (1.5 × 0.25 × 0.25) = 0.66푚3 Pad Foundations: 7 × (1.4 × 1.4 × 0.25) = 3.43푚3 Supporting concrete and apron (Assume 10m apron length): 60푚 × 13.25푚2 = 795푚3 Counterweight Support housing (housing size: 5.5m×4.0m×2.0m)Assume 200mm thick walls: 2 × [(2 × 2 × 5.5 × 0.2) + (2 × 4 × 5.5 × 0.2) + (2 × 4 × 2 × 0.2)] = 32.8푚3
Therefore total volume of concrete required: 0.66 + 3.43 + 795 + 32.8 = 831.9푚3 According to (AECOM, 2014) The cost of C50 concrete is £103.82 per m3 therefore: 831.9푚3 × £103.82 = £86368 Steel Columns: Each column requires the following reinforcement Longitudinal reinforcement = 4 × 20mm diameter bars (1257mm2) length 1.5m therefore 0.013m3 required Transverse reinforcement = 6 × 6mm diameter bars (170mm2) length 0.688m therefore 0.0008 m3 required
Pad Foundations: Each pad requires the following reinforcement 4 × 20mm diameter bars (1257mm2) length 0.25m Therefore 0.0022 m3 required
Supporting concrete and apron: Only minimum reinforcement required therefore area of reinforcement per m 2000푚푚2 퐴 = 0.002 × 1000 × 1000 = 16m length 60m run therefore 푠,푚𝑖푛 푚 total area of steel 120000푚푚2 Therefore 1.92 m3 required
Counterweight Support Housing: Assume minimum reinforcement required for the purpose of costings 2 2 퐴푠,푚𝑖푛 = 0.002 × 2800000 = 5600푚푚 푝푒푟 ℎ표푢푠𝑖푛푔therefore 11200mm total Therefore 0.062 m3 required
There total tonnage of reinforcement required: Density of steel: 7850kg/m3
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(0.013 + 0.0008 + 0.0022 + 1.92 + 0.062) × 7850 = 15684푘푔 = 15.7 tonnes steel required
According to (AECOM, 2014) the cost for supply and fit including bars, tying wire, spacers, couplers and steel supports the cost per tonne = £1184.79 15.7푡표푛푛푒 × £1184.79 = £18601 Excavation Excavation of foundations: Total volume of riverbed to be removed for weir 3.6×30 3.6×30 + = 108푚2 × 4푚 = 432푚3 2 2 Total volume of riverbed to be removed for apron 16 × 54 × 1 = 864푚3 According to (AECOM, 2014) the cost to excavate the above quantity of river bed using an excavator is £10.89 per 푚3 therefore (432 + 864) × £10.89 = £14113 Excavation of river banks: Total volume of riverbanks to be removed to ensure smooth water flow Assume 15m length of banks to be excavated upstream of weir 3.6×30 3.6×30 + = 108푚2 × 15푚 = 1620푚3 2 2 10m length of banks assumed to be excavated downstream of weir 3.6×30 3.6×30 + = 108푚2 × 10푚 = 1080푚3 2 2 According to (AECOM, 2014) the cost to excavate the above quantity of river bank using an excavator is £10.89 per 푚3 therefore (1620 + 1080) × £10.89 = £29403 Soil/rocks The excavated banks of the river are to be replaced with gabion cages filled with rocks as it is a strong natural looking material that can be placed in the required shape to ensure a smooth transition of the bank from its natural shape to the shape required for the weir and then back again. Roughly 2/3’s of the volume calculated in excavation of river banks found above will be replaced with gabions 2 (1620 + 1080) × = 1800푚3 3 The gabions used will be PVC coated galvanized wire mesh box gabions, wire laced with graded broken stone filling. The cost per 푚3provided by (AECOM, 2014) is £135.03 therefore the total cost is: 1800푚3 × £135.03 = £243054 Cofferdam Installation Installation of cofferdams using driven steel sections with recovery value, including all plant for installation and dismantling; loss of materials; pumping and maintenance Excluding excavation and disposal of material – backfilling on completion. Cost range based on 12 weeks installation on soft-medium ground conditions (AECOM, 2014)
Each of the 3 cofferdams will be constructed to a depth between 5-10m and with a diameter or side length up to 20m
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Therefore cost per cofferdam according to (AECOM, 2014) £69000 to £75000 Therefore assume medium cost of £72000 per cofferdam 푇표푡푎푙 퐶표푠푡 푓표푟 푡ℎ푟푒푒 푐표푓푓푒푟푑푎푚푠 = £72000 × 3 = £216000 Crane hire The cost of a crane according to (AECOM, 2014) is £2840.06 a week. As the project is expected to take 130 day to complete (19 weeks) this will cost 19푤푒푒푘푠 × £2840.06 = £53961 Excavator hire The cost of a excavator according to (AECOM, 2014) is £3310.57 a week. As the project is expected to take 130 day to complete (19 weeks) this will cost 19푤푒푒푘푠 × £3310.57 = £62901 Labor The cost per week for the following workers according to (AECOM, 2014) are as follows: Agent: £1400.80 Senior Engineer: £1030.00 Engineers (assume 2 required): 2 × £824.00 = £1648 General Foreman: £906.40 Excavation gang (1 plant operator, 1 banksman): £36.05/hr working 10hr day and 5 day week=£1802.50 Concrete gang (assume 2 gangs) (1ganger, 2 skilled operatives, 4 unskilled operatives 1 plant operator) £101.73/hr working 10hr day and 5 day week = £10173 General labour (assume 10 required):£504.70 each =£5047.00 total Therefore the total weekly cost for labour: 1400.80 + 1030.00 + 1648 + 906.40 + 1802.50 + 10173 + 5047 = £22007.70
Therefore total cost for labour throughout the 19 weeks of the project 19 × £22007.70 = £418146.30 Ancillaries Accommodation and buildings according to (AECOM, 2014): Offices (80m2) (fixed charge): £1802.50 Stores (fixed charge): £618 Canteen (fixed charge): £1545 Therefore total cost: = £3965.50
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Appendix B River Modelling
Correlation between river flow at Teston and Lenside
40 June 35
30
25
20
15 y = 8.0426x FlowTestonat 10
5
0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Flow at Lenside
July 40 35 30 25 20
15 y = 7.5217x FlowTestonat 10 5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Flow at Lenside
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August 40 35 30 25 20 15 y = 6.2995x FlowTestonat 10 5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Flow at Lenside
Note: outlying flow values are excluded to allow for the same scale to be applied to each graph for ease of comparison.
Predictions of flow levels from 1960-1990 levels, based on (Cloke, et al., 2010, p. 3485)
Prediction of flow at Teston (% of 1960-1990) June July August 1960-1990 100 100 100 1990-2020 88.8 94.1 87.7 2020-2050 75.8 80.5 81.5 2050-2080 49.8 54.2 40
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Appendix C General Scheme Arrangement at Allington Weir
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Appendix D Guide to Calculations and Relationships for Hydro Unit
Ref Calculation/Explanation Result 1 Available Flow
Available flow is the flow that could be potentially utilised by the installed hydro-power unit.
퐴푣푎𝑖푙푎푏푙푒 퐹푙표푤 = 푆𝑖푡푒 퐹푙표푤 − 푀𝑖푛𝑖푚푢푚 푅푒푠𝑖푑푢푎푙 퐹푙표푤 = m3/s. Where:
Site Flow = the converted flow from the overall area of the weir to fit the
area of the hydro-power unit.
Minimum Residual Flow = the M.R.F. for the area covered by the hydro- power unit.
2 Net Head
Net head is the remaining hydraulic head after subtracting the losses.
푁푒푡 퐻푒푎푑 = 푇표푡푎푙 퐻푒푎푑 − 푊푎푡푒푟 퐷푒푝푡ℎ 퐷표푤푛푠푡푟푒푎푚 − 퐹푟𝑖푐푡𝑖표푛 퐿표푠푠푒푠 = m Where:
Friction Losses = sourced from the friction between the coarse screen and
the flow of water (taken as 15mm). 3 Head Efficiency (Muller Head efficiency is the theoretical efficiency of the screw turbine in terms & of the difference of water depth between the inlet and the outlet. Senior, 2009) 푑 1 + 2 푑 휂 = 1 2 = unit less
Where:
d = the downstream water depth. 2
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d1 = the upstream water depth.
4 Leakage Efficiency
(Lubitz, Leakage efficiency is the theoretical efficiency of the screw turbine in 2014) terms of the portion of water leaking from the turbine’s gaps.
푄 휂 = 1 − 퐿 푄 = unit less.
Where:
QL = the leakage volume per second = 2.5 × 푠 × 퐷 × √퐷
Q = the flow-rate in the turbine.
D = the screw’s diameter.
1 s = gap width ≤ 0.0045 퐷2
Turbine Efficiency 5
Turbine efficiency is the overall efficiency at which the turbine is
theoretically going to be running.
휂 = 푙푒푎푘푎푔푒 푒푓푓𝑖푐𝑖푒푛푐푦 × ℎ푒푎푑 푒푓푓𝑖푐𝑖푒푛푐푦 = unit less.
6 Gearbox & Generator Efficiency
The gearbox and generator efficiencies are a result of the input power minus the power losses to obtain the output power.
The values used are obtained by company catalogues and alternated with = unit less. the input power. References are given.
7
Transmission Efficiency
Transmission efficiency is the efficiency of the transmission cable in
terms of the input electricity and the electricity output at the station that it
=unit less.
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8 is connected. Following similar hydro-power feasibility studies, the figure was taken as 99%.
Water-to-Wire Efficiency
Water to wire efficiency is the resulting efficiency of the hydro-power =unit less. scheme before cable transmission.
푊푎푡푒푟 − 푡표 − 푊𝑖푟푒 퐸푓푓𝑖푐𝑖푒푛푐푦 = 푇푢푟푏𝑖푛푒 퐸푓푓𝑖푐𝑖푒푛푐푦 × 9 퐺푒푎푟푏표푥 퐸푓푓𝑖푐𝑖푒푛푐푦 × 퐺푒푛푒푟푎푡표푟 퐸푓푓𝑖푐𝑖푒푛푐푦
(Muller & Power Output Senior, 2009) Power output is the un-factored potential amount of power that the turbine = kW. can produce at a fixed flow-rate and hydraulic head.
푃 = 휌 × 푔 × 푄 × ℎ
Where:
ρ = the density of water.
g = gravitational acceleration.
Q = utilised flow-rate. 10 h = available hydraulic head.
Available Power Output
Available power output is the factored amount of power that the turbine = unit less. can produce at a fixed flow-rate and hydraulic head.
푃푎푣 = 푃 × 푊푎푡푒푟 − 푡표 − 푊𝑖푟푒 퐸푓푓𝑖푐𝑖푒푛푐푦
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Appendix E Turbine Locations
Allington Weir Location, Turbine Diameter = 1meter. Minimum Gearbox Water-to- Available Annual Site Residual Available Utilised Maximum Net Head Leakage Turbine & Generator Transmission Wire Power Hydraulic Time Power 3 3 3 3 Flow (m /s) Flow (m /s) Flow (m /s) Flow (m /s) Head (m) Head (m) Efficiency (η1) Efficiency (η2) Efficiency (η3) Efficiency (η4) Efficiency (η5) Efficiency (η6) Output (kW) Power (kW) Usage (%) Generation (kWh) Qn (%) 1.00 9.04 0.21 8.83 0.38 4.65 2.89 0.81 0.97 0.79 0.85 0.99 0.67 17.30 11.39 USE 4990.83 5.00 5.17 0.21 4.96 0.38 4.65 3.03 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.60 USE 5081.48 10.00 1.86 0.21 1.65 0.38 4.65 3.04 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.61 USE 5086.11 15.00 1.49 0.21 1.28 0.38 4.65 3.04 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.62 USE 5090.74 20.00 1.24 0.21 1.03 0.38 4.65 3.05 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.63 USE 5095.37 25.00 0.96 0.21 0.75 0.38 4.65 3.06 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.64 USE 5099.34 30.00 0.79 0.21 0.58 0.38 4.65 3.06 0.83 0.97 0.80 0.85 0.99 0.68 17.30 11.65 USE 5103.97 35.00 0.70 0.21 0.49 0.38 4.65 3.07 0.83 0.97 0.81 0.85 0.99 0.68 17.30 11.66 USE 5108.60 40.00 0.60 0.21 0.39 0.38 4.65 3.08 0.83 0.97 0.81 0.85 0.99 0.68 17.30 11.68 USE 5113.90 45.00 0.44 0.21 0.23 0.23 4.65 3.09 0.83 0.95 0.79 0.84 0.99 0.66 10.60 6.94 USE 3041.25 50.00 0.38 0.21 0.17 0.17 4.65 3.09 0.83 0.93 0.78 0.83 0.99 0.64 7.65 4.86 USE 2130.32 55.00 0.33 0.21 0.11 0.11 4.65 3.10 0.83 0.90 0.75 0.83 0.99 0.62 5.19 3.19 USE 1395.90 60.00 0.31 0.21 0.09 0.09 4.65 3.11 0.83 0.88 0.73 0.83 0.99 0.61 4.27 2.57 USE 1124.14 65.00 0.28 0.21 0.07 0.07 4.65 3.11 0.83 0.83 0.69 0.83 0.99 0.57 3.01 1.70 USE 746.72 70.00 0.23 0.21 0.02 0.02 4.65 3.12 0.84 0.37 0.31 0.81 0.99 0.25 0.82 0.20 DON’T USE 0.00 75.00 0.21 0.21 0.00 0.00 4.65 3.13 0.84 0.00 0.00 0.80 0.99 0.00 0.11 0.00 DON’T USE 0.00 80.00 0.20 0.21 0.00 0.00 4.65 3.13 0.84 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 85.00 0.19 0.21 0.00 0.00 4.65 3.14 0.84 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 90.00 0.18 0.21 0.00 0.00 4.65 3.15 0.84 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 95.00 0.21 0.21 0.00 0.00 4.65 3.16 0.84 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 99.00 0.19 0.21 0.00 0.00 4.65 3.46 0.87 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 Proposed Installation Max Power Output (kW) 17.30 Max Head (m) 4.65 Friction Head Loss (m) 0.15 Design Flow (m3/s) 0.38 Min Power Output (kW) 0.00 Max Net Head (m) 3.46 Screw Intake Head (m) 4.50 MRF (m3/s) 0.21 Mean Power Output (kW) 7.65 Min Net Head (m) 2.89 Mean Flow (m3/s) 0.17
System Sizing Total Annual Power Output( kWh) 54208.67 CO2 Saved (tonnes) 26.04 Screw Outer Diameter (m) 1.00 Angle (o) 22.00 Results 2% Downtime Assumed 1084.17 Screw Inside Diameter (m) 0.50 No. of Blades 12.00 Estimated Annual Power Output (kWh) 53124.49 Screw Length (m) 12.41 Overall Efficiency 0.64 Total Downtime (%) 32.00
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TIDAL WATER RESOURCES | TEAM MEDWAY
Allington Weir Location, Turbine Diameter = 2 meters.
Minimum Gearbox Water-to- Available Annual Site Residual Available Utilised Maximum Net Head Leakage Turbine & Generator Transmission Wire Power Hydraulic Time Power 3 3 3 3 Flow (m /s) Flow (m /s) Flow (m /s) Flow (m /s) Head (m) Head (m) Efficiency (η1) Efficiency (η2) Efficiency (η3) Efficiency (η4) Efficiency (η5) Efficiency (η6) Output (kW) Power (kW) Usage (%) Generation (kWh) Qn (%) 1.00 15.07 0.21 14.86 0.63 4.65 2.89 0.81 0.93 0.75 0.88 0.99 0.67 28.83 19.00 USE 8319.82 5.00 8.61 0.21 8.40 0.63 4.65 3.03 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.34 USE 8470.93 10.00 3.10 0.21 2.89 0.63 4.65 3.04 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.36 USE 8478.65 15.00 2.48 0.21 2.27 0.63 4.65 3.04 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.38 USE 8486.37 20.00 2.07 0.21 1.86 0.63 4.65 3.05 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.39 USE 8494.09 25.00 1.61 0.21 1.40 0.63 4.65 3.06 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.41 USE 8500.71 30.00 1.31 0.21 1.10 0.63 4.65 3.06 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.43 USE 8508.43 35.00 1.17 0.21 0.96 0.63 4.65 3.07 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.44 USE 8516.15 40.00 1.01 0.21 0.79 0.63 4.65 3.08 0.83 0.93 0.77 0.88 0.99 0.68 28.83 19.46 USE 8524.98 45.00 0.74 0.21 0.53 0.53 4.65 3.09 0.83 0.91 0.76 0.88 0.99 0.67 24.10 16.04 USE 7023.68 50.00 0.63 0.21 0.42 0.42 4.65 3.09 0.83 0.89 0.74 0.88 0.99 0.66 19.18 12.47 USE 5463.83 55.00 0.54 0.21 0.33 0.33 4.65 3.10 0.83 0.86 0.72 0.87 0.99 0.63 15.08 9.39 USE 4112.19 60.00 0.51 0.21 0.30 0.30 4.65 3.11 0.83 0.85 0.71 0.87 0.99 0.62 13.55 8.30 USE 3634.72 65.00 0.46 0.21 0.25 0.25 4.65 3.11 0.83 0.82 0.69 0.87 0.99 0.60 11.44 6.78 USE 2971.02 70.00 0.38 0.21 0.17 0.17 4.65 3.12 0.84 0.74 0.62 0.86 0.99 0.53 7.79 4.10 USE 1796.65 75.00 0.36 0.21 0.15 0.15 4.65 3.13 0.84 0.69 0.58 0.86 0.99 0.50 6.62 3.27 USE 1431.39 80.00 0.33 0.21 0.12 0.12 4.65 3.13 0.84 0.62 0.52 0.86 0.99 0.44 5.39 2.36 USE 1035.63 85.00 0.31 0.21 0.10 0.10 4.65 3.14 0.84 0.56 0.47 0.86 0.99 0.40 4.70 1.88 USE 822.27 90.00 0.30 0.21 0.09 0.09 4.65 3.15 0.84 0.48 0.40 0.86 0.99 0.34 3.93 1.33 DON’T USE 0.00 95.00 0.21 0.21 0.00 0.00 4.65 3.16 0.84 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 99.00 0.19 0.21 0.00 0.00 4.65 3.46 0.87 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00
Proposed Installation Max Power Output (kW) 28.83 Max Head (m) 4.65 Friction Head Loss (m) 0.15 Design Flow (m3/s) 0.63 Min Power Output (kW) 0.00 Max Net Head (m) 3.46 Screw Intake Head (m) 4.50 MRF (m3/s) 0.21 Mean Power Output (kW) 19.18 Min Net Head (m) 2.89 Mean Flow (m3/s) 0.42
System Sizing Total Annual Power Output( kWh) 104591.53 CO2 Saved (tonnes) 50.25 Screw Outer Diameter (m) 2 Angle (o) 22 Results 2% Downtime Assumed 2091.83 Screw Inside Diameter (m) 1 No. of Blades 12 Estimated Annual Power Output (kWh) 102499.70 Screw Length (m) 12.41 Overall Efficiency 0.66 Total Downtime (%) 12.00
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TIDAL WATER RESOURCES | TEAM MEDWAY
Allington Weir Location, Turbine Diameter = 4 meters.
Minimum Gearbox Water-to- Available Annual Site Residual Available Utilised Maximum Net Head Leakage Turbine & Generator Transmission Wire Power Hydraulic Time Power 3 3 3 3 Flow (m /s) Flow (m /s) Flow (m /s) Flow (m /s) Head (m) Head (m) Efficiency (η1) Efficiency (η2) Efficiency (η3) Efficiency (η4) Efficiency (η5) Efficiency (η6) Output (kW) Power (kW) Usage (%) Generation (kWh) Qn (%) 1.00 27.12 0.21 26.91 1.14 4.65 2.89 0.81 0.84 0.68 0.88825 0.99 0.61 51.89 31.15 USE 13645.40 5.00 15.50 0.21 15.29 1.14 4.65 3.03 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.72 USE 13893.23 10.00 5.58 0.21 5.37 1.14 4.65 3.04 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.75 USE 13905.90 15.00 4.47 0.21 4.26 1.14 4.65 3.04 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.78 USE 13918.56 20.00 3.72 0.21 3.51 1.14 4.65 3.05 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.81 USE 13931.22 25.00 2.89 0.21 2.68 1.14 4.65 3.06 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.83 USE 13942.08 30.00 2.36 0.21 2.15 1.14 4.65 3.06 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.86 USE 13954.74 35.00 2.11 0.21 1.89 1.14 4.65 3.07 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.89 USE 13967.40 40.00 1.81 0.21 1.60 1.14 4.65 3.08 0.83 0.84 0.70 0.88825 0.99 0.62 51.89 31.92 USE 13981.88 45.00 1.33 0.21 1.12 1.12 4.65 3.09 0.83 0.84 0.70 0.88825 0.99 0.62 51.09 31.36 USE 13735.27 50.00 1.14 0.21 0.93 0.93 4.65 3.09 0.83 0.81 0.67 0.88825 0.99 0.60 42.25 24.92 USE 10913.38 55.00 0.98 0.21 0.76 0.76 4.65 3.10 0.83 0.76 0.64 0.8835 0.99 0.56 34.85 19.41 USE 8503.44 60.00 0.92 0.21 0.70 0.70 4.65 3.11 0.83 0.74 0.62 0.8835 0.99 0.55 32.11 17.43 USE 7635.56 65.00 0.83 0.21 0.62 0.62 4.65 3.11 0.83 0.71 0.59 0.8835 0.99 0.52 28.31 14.68 USE 6428.86 70.00 0.69 0.21 0.48 0.48 4.65 3.12 0.84 0.62 0.52 0.874 0.99 0.45 21.74 9.78 USE 4282.31 75.00 0.64 0.21 0.43 0.43 4.65 3.13 0.84 0.58 0.49 0.874 0.99 0.43 19.63 8.26 USE 3618.53 80.00 0.59 0.21 0.38 0.38 4.65 3.13 0.84 0.53 0.44 0.874 0.99 0.39 17.42 6.67 USE 2920.19 85.00 0.57 0.21 0.35 0.35 4.65 3.14 0.84 0.49 0.41 0.8645 0.99 0.36 16.18 5.71 USE 2501.03 90.00 0.54 0.21 0.32 0.32 4.65 3.15 0.84 0.44 0.37 0.8645 0.99 0.32 14.78 4.72 USE 2065.34 95.00 0.21 0.21 0.00 0.00 4.65 3.16 0.84 0.00 0.00 0 0.99 0.00 0.00 0.00 DON’T USE 0.00 99.00 0.19 0.21 0.00 0.00 4.65 3.46 0.87 0.00 0.00 0 0.99 0.00 0.00 0.00 DON’T USE 0.00
Proposed Installation Max Power Output (kW) 51.89 Max Head (m) 4.65 Friction Head Loss (m) 0.15 Design Flow (m3/s) 1.14 Min Power Output (kW) 0.00 Max Net Head (m) 3.46 Screw Intake Head (m) 4.50 MRF (m3/s) 0.21 Mean Power Output (kW) 42.25 Min Net Head (m) 2.89 Mean Flow (m3/s) 0.93
System Sizing Total Annual Power Output( kWh) 187744.33 Screw Outer Diameter (m) 4 Angle (o) 22 CO2 Saved (tonnes) 90.20 Results 2% Downtime Assumed 3754.89 Screw Inside Diameter (m) 2 No. of Blades 12 Estimated Annual Power Output (kWh) 183989.44 Screw Length (m) 12.41 Overall Efficiency 0.60 Total Downtime (%) 8.00
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TIDAL WATER RESOURCES | TEAM MEDWAY
Moveable Weir Location, Turbine Diameter = 2 meters Winter Period Example.
Minimum Gearbox Water-to- Available Annual Site Residual Available Utilised Maximum Net Head Leakage Turbine & Generator Transmission Wire Power Hydraulic Time Power 3 3 3 3 Flow (m /s) Flow (m /s) Flow (m /s) Flow (m /s) Head (m) Head (m) Efficiency (η1) Efficiency (η2) Efficiency (η3) Efficiency (η4) Efficiency (η5) Efficiency (η6) Output (kW) Power (kW) Usage (%) Generation (kWh) Qn (%) 1.00 5.10 0.09 5.01 0.66 1.20 0.00 0.50 0.93 0.47 0.78 0.99 0.36 7.78 2.80 USE 912.43 5.00 3.16 0.09 3.08 0.66 1.20 0.00 0.50 0.93 0.47 0.78 0.99 0.36 7.78 2.80 USE 912.43 10.00 1.73 0.09 1.65 0.66 1.20 0.00 0.50 0.93 0.47 0.78 0.99 0.36 7.78 2.80 USE 912.43 15.00 0.79 0.09 0.71 0.66 1.20 0.00 0.50 0.93 0.47 0.78 0.99 0.36 7.78 2.80 USE 912.43 20.00 0.66 0.09 0.57 0.57 1.20 0.00 0.50 0.92 0.46 0.78 0.99 0.36 6.76 2.40 USE 783.82 25.00 0.55 0.09 0.46 0.46 1.20 0.00 0.50 0.90 0.45 0.77 0.99 0.35 5.41 1.86 USE 606.53 30.00 0.43 0.09 0.34 0.34 1.20 0.00 0.50 0.87 0.43 0.77 0.99 0.33 4.05 1.34 USE 437.50 35.00 0.35 0.09 0.26 0.26 1.20 0.00 0.50 0.83 0.41 0.77 0.99 0.32 3.10 0.98 USE 319.62 40.00 0.25 0.09 0.16 0.16 1.20 0.00 0.50 0.73 0.36 0.76 0.99 0.28 1.93 0.53 USE 172.25 45.00 0.21 0.09 0.13 0.13 1.20 0.00 0.50 0.65 0.32 0.76 0.99 0.25 1.49 0.36 USE 118.48 50.00 0.13 0.09 0.05 0.05 1.20 0.00 0.50 0.04 0.02 0.76 0.99 0.01 0.55 0.01 DON’T USE 0.00 55.00 0.09 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.67 0.99 0.00 0.02 0.00 DON’T USE 0.00 60.00 0.03 0.09 0.00 0.00 1.20 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 65.00 -0.02 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 70.00 -0.05 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 75.00 -0.07 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 80.00 -0.10 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 85.00 -0.12 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 90.00 -0.18 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 95.00 -0.23 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00 99.00 -0.27 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 0.00 DON’T USE 0.00
Proposed Installation Max Power Output (kW) 7.78 Max Head (m) 1.20 Friction Head Loss (m) 0.15 Design Flow (m3/s) 0.66 Min Power Output (kW) 0.00 Max Net Head (m) 0.00 Screw Intake Head (m) 1.05 MRF (m3/s) 0.09 Mean Power Output (kW) 0.55 Min Head (m) 0.00 Mean Flow (m3/s) 0.05
System Sizing Total Annual Power Output( kWh) 6087.92 Screw Outer Diameter (m) 2 Angle (o) 22 CO2 Saved (tonnes) 2.92 Results 2% Downtime Assumed 121.76 Screw Inside Diameter (m) 1 No. of Blades 8 Estimated Annual Power Output (kWh) 5966.16 Screw Length (m) 3.2 Overall Efficiency 0.16 Total Downtime (%) 52.00
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TIDAL WATER RESOURCES | TEAM MEDWAY
Moveable Weir Location, Turbine Diameter = 2 meters Summer Period Example.
Minimum Gearbox Water-to- Available Annual Site Residual Available Utilised Maximum Net Head Leakage Turbine & Generator Transmission Wire Power Hydraulic Time Power 3 3 3 3 Flow (m /s) Flow (m /s) Flow (m /s) Flow (m /s) Head (m) Head (m) Efficiency (η1) Efficiency (η2) Efficiency (η3) Efficiency (η4) Efficiency (η5) Efficiency (η6) Output (kW) Power (kW) Usage (%) Generation (kWh) Qn (%) 1.00 0.13 0.09 0.04 0.04 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.51 0.00 DON’T USE 0.00 5.00 0.03 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 10.00 -0.06 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 15.00 -0.08 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 20.00 -0.09 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 25.00 -0.09 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 30.00 -0.10 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 35.00 -0.11 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 40.00 -0.12 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 45.00 -0.14 0.09 0.00 0.00 1.20 0.00 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 50.00 -0.15 0.09 0.00 0.00 1.20 0.01 0.50 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 55.00 -0.16 0.09 0.00 0.00 1.20 0.19 0.58 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 60.00 -0.17 0.09 0.00 0.00 1.20 0.39 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 65.00 -0.18 0.09 0.00 0.00 0.00 0.59 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 70.00 -0.19 0.09 0.00 0.00 0.00 0.75 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 75.00 -0.21 0.09 0.00 0.00 0.00 0.91 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 80.00 -0.21 0.09 0.00 0.00 0.00 1.02 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 85.00 -0.23 0.09 0.00 0.00 0.00 1.12 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 90.00 -0.23 0.09 0.00 0.00 0.00 1.20 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 95.00 -0.25 0.09 0.00 0.00 0.00 1.20 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00 99.00 -0.26 0.09 0.00 0.00 0.00 1.20 0.00 0.00 0.00 0.99 0.85 0.00 0.00 0.00 DON’T USE 0.00
Proposed Installation Max Power Output (kW) 0.51 Max Head (m) 1.20 Friction Head Loss (m) 0.15 Design Flow (m3/s) 0.04 Min Power Output (kW) 0.00 Max Net Head (m) 1.20 Screw Intake Head (m) 1.05 MRF (m3/s) 0.09 Mean Power Output (kW) 0.00 Min Head (m) 0.00 Mean Flow (m3/s) 0.00
System Sizing Total Annual Power Output( kWh) 0.00 Screw Outer Diameter (m) 2 Angle (o) 22 CO2 Saved (tonnes) 0.00 Results 2% Downtime Assumed 0.00 Screw Inside Diameter (m) 1 No. of Blades 8 Estimated Annual Power Output (kWh) 0.00 Screw Length (m) 3.2 Overall Efficiency 0.00 Total Downtime (%) 100.00
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TIDAL WATER RESOURCES | TEAM MEDWAY
Appendix F Salinity graphs
These graphs were created using the modelling software ISIS and by data provided by (Cutting, 2014). The data however is very rough and more data should definitely be collected after the feasibility study if the project it to commence. However with the limited data it can be seen on the high tide at high abstraction levels and the high tide with low abstraction levels that the graph very loosely follows a salt-wedge boundary layer assumption.
Figure 26-1 High tide at high abstraction levels
Figure 26-2Low tide at high abstraction levels
AGILESH SINGARAJ SALINITY GRAPHS PAGE | 181 TIDAL WATER RESOURCES | TEAM MEDWAY
Figure 26-3 High tide at low abstraction levels
Figure 26-4 Low tide at low abstraction levels
AGILESH SINGARAJ SALINITY GRAPHS PAGE | 182