Canadian Consulting Engineer

Computer Modelling for Water

July 1, 2008   Canadian Consulting Engineer

POWER

Finding Run-of-River Hydroelectricty Potential in B.C.

Kerr Wood Leidal Associates

British Columbia has set aggressive targets for greenhouse gas emission reductions. An important source of clean electricity is run-of-river hydropower.

Kerr Wood Leidal Associates (KWL) was retained by BC Hydro and the British Columbia Transmission Corporation to identify all potential run-of-river hydroelec-tricity sites in B. C. Using conventional methods, the task would take years to complete.

KWL applied its Rapid Hydropower Assessment Model (RHAM), a powerful geographic information systems (GIS)-based computer model, which enabled the assessment to be completed in an astonishing four months!

RHAM was developed using an ArcGIS 9.2 platform with the Spatial Analyst extension from ESRI Canada. GIS data sources incorporated into the model included Digital Elevation Model (DEM) data from Natural Resources Canada and hydrology data from the B. C. Ministry of Environment. RHAM was run for the entire province. Standard methods, in contrast, would have examined only those sites that were near transmission lines and appeared promising.

Using DEM and mean annual surface run-off information, RHAM’s unique algorithm can identify every significant stream and river within a given area, their respective flow rates throughout the year, and maximum elevation drops along each reach within a given distance. The model does this by running both a topographical and a hydrological analysis simultaneously. It then generates a run-of-river power potential, including the associated head (i. e. elevation drop) of any given watercourse at varying penstock lengths between 500 metres and 5,000 metres, and it identifies intake sites.

Identifying potential sites and hydropower potential, paints only part of the picture. To be of value, sites must be economically viable. KWL used RHAM’s GIS capabilities to prepare capital cost estimates for components such as penstocks, weirs, pumps and powerhouses based on each site’s unique characteristics.

To calculate the cost of access roads and transmission lines for each site, RHAM factored in the slope of the land to be traversed, distance from a major centre, land cover, hydrologic features, and presence of forestry roads.

From this analysis, RHAM identified 8,200 viable sites, representing over 50,000 gigawatt-hours of electricity per year. The program automatically mapped their corresponding optimal routes for new roads and transmission lines.

Although the model performed well from the first, KWL made adjustments to ensure that it provided accurate results. For example, in some flat areas the engineers corrected the DEM data to ensure that streams flowed in the correct direction. Stream-flow calculations were adjusted for streams flowing into B. C. from interprovincial watersheds.

Project team: Mike Homenuke, EIT, Stefan Joyce, P. Eng., Jack Lau, Tech., Ron Monk, P. Eng., Karl Mueller, P. Eng., Alex Wood, P. Eng.

ENVIRONMENT

Realtime Flood Forecasting in Lower Fraser Valley, B.C.

Northwest Hydraulic Consultants, Vancouver

The lower Fraser Valley, home to 300,000 people, extends for a distance of 170 kilometres from the District of Hope to the Strait of Georgia. There have been two devastating floods in the valley since European settlement, one in 1894 and another in 1948. Since 1948 over $300 million has been spent to construct and maintain flood control structures along the river. The environmental and economic cost from another major flood could be in the billions.

The Fraser Basin Council, a non-governmental organization, was charged with finding the best flood protection. In 2005, the council retained Northwest Hydraulic Consultants (NHC) to develop a state-of-the-art numerical model of the Fraser River, based on detailed surveys of the channel and floodplain.

The model uses a one-dimensional hydrodynamic software package developed by the Danish Hydraulic Institute called MIKE11. The model includes over 1,200 river cross-sections describing the main and side channels between Hope and the ocean.

The project team faced several technical challenges in developing the model:

• Flow is affected by tides due to the low channel gradient, and is subject to flow reversal in the lower 50 kilometres of the river. The model was run hydrodynamically to address this issue.

• Ocean salt water, with a higher density than fresh water, forms a wedge in the lower river, causing stratification. The friction coefficient (roughness) in the salt water reaches was adjusted over the tidal cycle to account for this stratification.

• Large sand dunes form on the riverbed during high flows, increasing the resistance to flow in the channel. The model made allowance for this effect.

• Changes to the river since the last flood precluded calibrating the model to the 1894 adopted design flood. Therefore, a separate model using river surveys from the 1950s was developed and calibrated to the 1948 flood levels. The roughness coefficients derived from the historic model were then used in the up-to-date model.

The calibrated model was then used to calculate the water levels that would result from a recurrence of the 1894 flood of record.

The results showed that there is a serious flood threat along the river, with the potential for a number of dikes to be overtopped.

Prompted by the fact that the 2007 spring snow-pack was higher than usual, the B. C. Ministry of Environment retained NHC to run the model in real time to generate daily flood-level forecasts along the river, up to five days in advance. The flood-level forecasting was the first real-time flood modelling effort in British Columbia.

Using a sophisticated in-house database built in ArcMap 9.2 and Microsoft VisualBasic 6.3, forecasted flood levels were continuously compared with observed water levels at 75 river gauges to monitor the performance of the model. The modelled and observed levels were generally found to agree within 10 centimetres.

Project team: Dave McLean, Ph. D, P. Eng., Monica Mannerstrom, P. Eng., Tamsin Lyle, P. Eng., Sarah North

WATER TREATMENT

Driftpile Water Treatment Plant 3D Modelling, Alberta

ISL Engineering and Land Services, Edmonton

ISL Engineering designed a new water treatment plant for the Driftpile First Nation, located on the southern shore of Lesser Slave Lake in Alberta. The plant uses membrane filtration, ultra-violet and chlorine disinfection, along with a pressure filtration system for pre-treatment. It has a capacity of 817 cubic metres per day.

Recognizing that the plant’s ongoing success depends on it being competently operated, ISL developed a training program for the local First Nation Water Keepers. The training included detailed graphically enhanced 3D models of the entire plant and its operations. The model allows the operators a virtual “walk through” the plant from a first-person perspective. The training plan was executed by ISL with the prime construction contractor, Nason Contracting.

The benefit of using the 3-D images is that the operator can orient himself spatially and determine exactly which piece of equipment he is controlling or reading data from. He sees on the screen what he sees in the plant. For instance, if a valve fails to open, the operator can immediately correlate the location of the valve on the screen to the location on the plant floor. This is particularly useful for a relief operator, who may be unfamiliar with the plant.

Any group of components can be isolated in the 3D model and animated to demonstrate a specific process. For example, the process of replacing filters in the 1-micron prefilters can be shown as an animation on screen. Also the operator can “see” through different layers, for example to view equipment in the reservoir beneath th
e building.

Screen shots from the models were incorporated into the SCADA (supervisory control and data acquisition) system that the operators use to control the plant operations. Key information, run status, and control boxes were added to the 3-D screens to provide the necessary monitoring and control information.

To create the 3-D model, the engineers began with twodimensional drawings from the various equipment manufacturers and ISL’s own drawings for the building. The drawings were given selected colours and textures to reflect the real-world equipment. Software programs used were Autodesk AutoCAD, Autodesk 3D Studio Max and Adobe Photoshop. When rendering in 3D using 3D Studio Max, a box has eight faces (four exterior and four interior). Once the Driftpile model was completed it contained over 2 million faces. Rendering required up to 6 x 64-bit dual core AMD processors with 46B of RAM on Windows 64.

Project team for 3-D computer modelling: Deon H. J. Wilner,

P. Eng., Jason Kopan, P. Eng., Arthur Chin (ISL Engineering); Taylor Green, RET, Roxanne Yakemchuk, P. Eng. (Nason Contracting)

INFRASTRUCTURE

Sustainable Sewer Funding Model for New Westminster, B. C.

UMA Engineering

The city of Westminster near Vancouver was one of the first settlements in the Lower Mainland. It has over 240 kilometres of gravity sanitary, storm and combined sewers, with an estimated replacement value of approximately $170 million. It was widely thought that the system was in dire need of replacement due to its age.

The city has an excellent planned repair and replacement program based on condition assessment data and CCTV inspection data. However, while the data had been used to assess short term needs, it had never been assessed in a manner that provided a longer term view of the funding requirements.

The sustainable funding model developed by UMA used the real sewer condition data to determine optimum rehabilitation and reinspection funding ranges for each sewer type. The planning cycles ranged from 10 to 100 years or longer.

As textbook values for sewers have largely been developed based on ‘time value of money criteria’ as opposed to real observations of their physical degradation, people confuse the two and are rather uncomfortable with their first crack at making decisions based on real observations of deterioration rates.

UMA’s analysis showed the city that much of their older inventory was in very good condition and had no evidence of basic material degradation. In fact, the inventory could reasonably be expected to last much longer than conventional “textbook” values. The future was unlikely to be as gloomy as previously envisaged.

Several alternative funding scenarios were run, including:

• maintaining the status quo of current funding levels

• increasing funding at a constant rate over an initial period

• decreasing funding at a constant rate over an initial period.

Comparing these three alternatives illustrated that despite the fact that approximately the same amount of time-adjusted money was being spent over the planning period, each resulted in distinctly different levels of service, different risk profiles, and different systems for future generations to inherit.

Two sustainable funding model formats were developed in the form of dot net modified Excel spreadsheets, both combining a knowledge of rehabilitation costs at various stages in the deterioration cycle with a knowledge of deterioration rates from a Markov chain deterioration model.

Software used included Microsoft Access to manage and mine data, AutoCad Map and GeoMedia to perform spatial analysis. VB.net programming was used to develop the Linear Infrastructure Deterioration Forecasting Tool. This is a database mapping tool that can connect to any modern database software (e. g. MS Access, Oracle, SQL Server) as long as the necessary attributes are there.

Project team: Karen Leung, P. Eng., Brad Croft, P. Eng., Eymond Toupin, P. Eng., Kirby MacRae, P. Eng., Chris Macey, P. Eng.


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