Brief
Wessex Water is to supply the new development of 2000 houses in Poundbury with drinking water. It has been determined that a pumping station (PS) at Burton will supply water from the regional main to a service reservoir (SR) at Lambert’s Hill, which in turn will allow water to flow by gravity to the urban development. There are therefore two pipes that need to be designed, the pumped trunk main from Burton PS to Lambert’s Hill SR, and the gravity distribution main from Lambert’s Hill SR to Poundbury. You are tasked with examining the alternatives and proposing the most cost effective solutions; your designs will encompass the route, pipe material, pipe diameter and for the trunk main the outline pump arrangement, plus you will advise on the need for pressure surge protection.
The pipeline’s route will be governed by a number of factors, amongst them system hydraulics (ground elevation and slope), land use (landowners, road / rail and river crossings), sensitive areas (AONB, CWS, SSSI, SAM) and access (construction and maintenance). The pipeline’s diameter will be governed by system hydraulics (pressure, flow, friction, length) and the material will be governed by ground conditions and costs. The pertinent requirements from the Wessex Water Design Standards are given below (for more information please refer to the module website):
- General
- Trunk mains shall not be used to provide local supplies
- Design capacity
- Trunk mains shall be sized for peak week or maximum day demand
- Distribution mains shall be sized for peak hour demand on maximum day demand
- Design velocities
- Both minimum and maximum velocities shall be considered
- The diameter / velocity shall be optimized for pumping mains by calculating 60 year whole life cost
- Min velocity based on 12 hour retention time; max velocity < 2.0 m/s for trunk mains and < 1.5 m/s for distribution mains
- Hydraulic design
- Colebrook White (HR Wallingford look-up tables)
- Roughness values to allow for future deterioration
- Min pressure
- 6m anywhere along pipe
- Distribution mains must be >15m (design for 20m)
- Max pressure
- Where pressures in the distribution system are in excess of 35m consideration shall be given to the installation of PRVs (see section 18)
- Max pressure limited to 16 Bar in pumped trunk mains [e-mail from Wessex Water]
- Pipe pressure rating
- To account for hydraulic testing, surge and fatigue
- Material
- DI or PE
- Protection
- Soil survey is required
- Jointing
- Assume costs cover industry standards (n/a)
- Gradients
- Thrust blocks are required for steep gradients (assume n/a)
- Crossings
- Major crossings (at railway lines, rivers and main roads) will require twin pipes with isolating valves to be laid
- Buried crossings preferred
- Cover and clearance
- Cover to crown of 0.9m to 1.3m
- Minimum separation from other pipes / ducts / cables of 500mm
- Swabbing chambers
- Every 2.5km or less
- Thrust blocks
- Required on bends / branches where pipelines not continuous or pipe material does not possess adequate tensile strength
- Valves
- In-line valves every 2km or less
- Air valves at high points
- Hydrants and washouts
- Washout valves at low points
- PRVs
- Shall be installed as required
In evaluating the options, your report must:
- Use outline design to size appropriate pipes of appropriate materials
- Address the costs and relative benefits of each scheme using Net Present Value
- Make a recommendation as to which scheme should be taken forward to detailed design
- Use performance curves to select pumps for Duty / Standby / Assist operation
- Advise of the need for pressure surge protection
Format
Using 11-point Arial font with 1.5 line spacing and 3cm margins, the text within the report must not exceed 3000 words (~9 pages) in length. This limit applies to the main body of the report (introduction to conclusions), excluding figures, graphs and tables. Below is a suggested format for the report; the UWE generic marking scheme will be used to grade your reports.
- Title page – suitable heading identifying the subject of the report, plus the author’s student number and date it was completed.
- Summary – brief description (~100 words) of the work that was undertaken and the outcome; it should have sufficient detail to allow someone to determine whether the report will contain the information they require. The Summary is a simplified combination of the Introduction and Conclusions; it will be read first but written last.
- Contents – include section numbers as well as page numbers.
- Introduction – brief explanation of the design problem (the purpose of the report) to include the specification being used, plus the report’s structure.
- Investigations of route – explanation, assumptions
- Options considered
- Justification for selection of preferred pumped and gravity pipe routes
- Pipe design – explanation (including pipeline ancillaries such as PRVs, washout chambers, crossings etc), table of diameters and head-losses from pipe and fittings, assumptions
- Costs – explanation, justification for selection of preferred material / diameter, assumptions
- Pump – explanation, justification for selection of chosen Armstrong pump arrangement, assumptions
- Pressure surge – justification for recommendation of pressure surge analysis by an expert consultant
- Conclusions – preferred options; further work may also be identified in this section.
- References – Harvard style referencing of every source used; a bibliography can also be included to illustrate reading within the subject area.
- Appendices
- A3 plan of alternative routes and A4 (or A3) long section of chosen route
- Design calculations – pipe diameters of both pumped (DI) and gravity mains (DI and PE); design head-losses from pipe and fittings
- Spreadsheets of NPV for pumped main (DI) and CAPEX for gravity main (DI and PE)
- Calculation for system curve: H = 96.75 + F Q2 to derive a value for F
- Pump / system curve for 5 no. 200 x 290 x 280 showing correct operating point
- Reservoir / pipe / valve analysis to replicate pressure surge in both the pumped and gravity mains