Technical Flashcards
(18 cards)
Provide an example of where you have innovated?
I was looking into methods of discharging the Lincs reservoir’s emergency drawdown flow in a more interesting way such that it could become a public engagement feature.
The method, which I’m currently still developing, is to discharge the flow via a number of vertical fountains. I’ve been exploring the height the jet reaches, the energy dissipation achieved, the revetment required in the collection pond, and the required stage-storage relationship required in the pond.
What is cavitation?
Cavitation is caused by sudden changes in fluid pressure caused by sudden changes in the fluid’s velocity.
Gases come out of solution and then rapidly collapse back into solution causing a shock wave which can damage the pipe/components
What is the key legislation that reservoirs are subjected to?
The Reservoirs Act 1975 and Flood and Water Management Act 2010
When is a reservoir subject to the legislation of the Reservoirs Act 1975
A reservoir is classified as a large raised reservoir if its raised volume is greater than 25,000m3. In Scotland, Wales and Northern Ireland this threshold was reduced to 10,000m3 during the 2010s. (Scotland has it’s own Reservoirs Act 2011 to replace the 1975 act).
What are some of the design standards you have used to produce your designs
- Floods and Reservoir Safety, 2015 - defining the flood protection standards for the design of a replacement spillway at Cannop Ponds
- EA Guide to drawdown capacity for reservoir safety and emergency planning, 2017 for design of the emergency drawdown systems at Lincs reservoir and Cannop Ponds
- CIRIA Culvert, Screen and Outfall Manual for the design of a culvert associated with Calverley FSR Brook Diversion, for the design of debris and security screens for A494 Improvement Works, Cannop Ponds and for selecting manning’s roughness values.
- CIRIA Manual on scour at bridges and other hydraulic structures, and The Rock Manual for the detailed design of rip rap downstream of outfalls at South Perrott FSR, and Calverley FSR Brook Diversion Culvert
- USBR Hydraulic Design of Stilling Basins and Energy Dissipaters for concept designs of stilling aprons downstream of Cannop Ponds spillway and Lincs reservoir EDD pond
What are the different reservoir risk designations
A reservoir can be designated “high risk” if a breach event has potential to endanger human life.
Category A reservoirs have potential to endanger lives in a community (>10 people)
Category B reservoirs have potential to endanger lives not in a community or result in extensive damage.
Category C reservoirs have negligible risk to life and expected to cause limited damage in a breach scenario
Category D are special cases where no loss of life is foreseen
What legislation applies to reservoirs not subject to the Reservoirs Act
These would be subject to the Buildings Act 1984 in which local authorities can act if the reservoir is deemed a Dangerous Building. Civil Law also applies in which all have a duty of care to others.
What assumptions did you make in the design of your emergency drawdown system
To name a few:
To size the pipework, a high pipe roughness was assumed as it was assumed the pipework would be accumulate bio-slimes and mineral deposits over time.
For the purpose of designing the fountain, a low pipe roughness was assumed such that the fountain height and energy to be dissipated was at its highest.
Flows through the scour pipe would be unaffected by the downstream conditions. In the design of the fountain and EDD pond I need to check this assumption remains true.
What assumptions went into the hydraulic model
- EDD channel based on manning’s calcs. Slight deviations in manning’s roughness can have significant impacts to flow rate. Manning’s roughness can also change with time as high flows alter the surface. Sensitivity tests to be completed to assess how changing roughness impacts required channel size.
- Model built using EA LiDAR data for out of bank topography, bathymetry data for channels. LiDAR only accurate to +-15cm so a deviation in ground level can affect estimated flood depths. LiDAR accuracy typically better in open areas and is less accurate in urban/heavily forested areas and dataset can be distorted by the tree canopy and roof tops.
- Tidally locked Black Sluice based on spring tides using 2125 predictions for sea level rise.
How did you make sure quality was maintained throughout your deliverables on Lincs reservoir
Where I was the design author, I requested a technical check by a Chartered Civil Engineer. Following their check, I requested technical approval from the reservoir design lead - a reservoir Supervising Engineering. All design matters relating to reservoir safety needed subsequent approval from the Construction Engineer - a member of the All Reservoir Panel Engineer. All design matters relating to reservoir safety were also put forward to the Independent Reservoir Expert Panel - a panel made up of All Reservoir Panel Engineers and Supervising Engineers
What are the RIBA plan of work stages and what stages have your projects been at.
Stage 0 - Strategic Definition
Stage 1 - Preparation and Briefing
Stage 2 - Concept Design - Lincs and Fens
Stage 3 - Spatial Co-ordination
Stage 4 - Technical Design
Stage 5 - Manufacturing and Construction
Stage 6 - Handover
Stage 7 - Use
What is the overall basis of the design for the Lincs reservoir? Why is it being built?
Anglian Water have completed Water Resource Management Plans (WRMPs) at the end of the last two Asset Management Periods (AMP cycles run for 5 years) in 2019 (AMP6) and 2024 (AMP7).
Lincs reservoir identified in WRMP19 in the feasible options set for new supply resources (desalination plant also considered).
Lincs reservoir is an earth embankment non-impounding reservoir positioned between three ridgelines on the edge of the Lincolnshire fens. It will provide winter storage during periods of high river flow in which water is pumped to the reservoir from abstraction sources close by.
It is being built to reduce Anglian Water’s anticipated 2045 supply-demand deficit with population growth and climate change being key causes for this deficit.
How do you design an earth embankment dam?
The design of the embankment itself I’ve not got direct experience with but some of the key principles for the Lincs reservoir are as follows:
- A clay core with low permeability provides the reservoir with the ability to retain water.
- Structural fill is placed either side of the core to provide the core with structural stability (1 in 5.5 slopes)
- Landscaping fill is placed on top of the structural fill on the downstream shoulder to enable planting, construction of paths and cycleways etc.
- Just downstream of the clay core, a sand chimney drain and blanket drain alleviates the build up of pore water pressure. Toe drains discharge seepage flows and prevent a build up of water at the toe.
- A key trench in the foundation lengthens groundwater flow paths to reduce below foundation seepage flows.
- A spillway provides a means of safely discharging excess flows, should the supply pumps fail to turn off.
- The drawoff tower contains the valves and pipework for supply outflows to the WTW, and for emergency drawdown
- Sections of the downstream toe are kept without landscaping fill to enable better inspection of the structural fill.
- Current concept design is to use site won fill from an excavated borrow pit (Glacial Till overlying Oxford Clay) then import sand and gravels for the chimney drains
How is the Lincs reservoir being funded?
As a piece of nationally important infrastructure Lincs reservoir is receiving some public funding through the Regulators Alliance for Progressing Infrastructure Development (RAPID) - made up of Ofwat, the EA and the Drinking Water Inspectorate.
Primarily the reservoir is being funded by Anglian Water and their revenue streams e.g. customer bills.
How do you design a reinforced concrete wall or slab
I’ve not completed reinforced concrete design to any great detail.
However, an example of where I’ve specified reinforced concrete retaining walls and slabs is on Cannop Ponds for the replacement spillway which I’m currently designing.
We’re at the concept design stage for the project currently with no structural engineer currently resourced to the project.
The retaining walls are circa 2m high so I’ve currently specified a thickness of 400mm. I’ve assumed this to be conservative based on previous as-built drawings I’ve seen for other projects. At this thickness it should enable the structural engineer to consider different types of wall construction (masonry, sheet, secant).
Once the structural engineer is appointed, I would co-ordinate with the geotech engineers to provide them with the soil characteristics and the loads acting on the wall
How do you calculate the flow in a pipe?
Depends on the input parameters you know but:
- Simplest calc is flow velocity x flow area
- Bernoulli’s equation which builds on the principle of conservation of energy.
– Total Head is constant throughout
– Total Head = Pressure head + Velocity head + Elevation head + Friction losses + Minor/Local losses - Friction loss calculated using Darcy-Weisbach equation
– Can be calculated manually using a Moody diagram Reynolds number (related to flow turbulence)
How do you calculate the reservoir volume for drawdown analysis
A 3D model on Civil 3D is being developed by our CAD specialists using the reservoir concept design provided by the landscape architects.
Using the 3D model surfaces for the Top Water Level and the reservoir basin, I requested the production of a ‘volume surface’ which essentially takes one surface from the other.
Using that volume surface I’m able to export stage-storage data at 0.1m level bands to establish the volume to be discharged at the required 5%H/day rate
How have you considered the contractor’s need to provide temporary works in your design for the permanent works?
For Cannop Pond’s spillway design I’ve been designing new, higher spillway walls to contain the 1 in 10,000yr flood. Down the chute, on the hydraulic right of the channel, the valley side is very steep and at the top of the hill is a stoneworks so quite high loads acting on this hillside.
Initial thought for replacement spillway is to demolish the old and construct the new however,
- Old spillway wall might be acting to retain hillside above,
- Even if not, the contractor would need to batter back further into the hillside to remove the old and construct the new, risking the structural stability of the hillside.
At this concept design stage, I’ve instead specified that the existing wall will remain in place, and the spillway will be realigned such that the new wall will be constructed next to the existing, to avoid the need to batter back.
