The consulting’ firm of Charles Howard and Associates has worked to
develop a series of rule curves that relate the volume of water in
storage at a given date to the level of demand that can be sustained
wi that exceeding a pre-determined risk of supply shortfall by the
selected target date., An example of such a curve is attached. Capilano
and Seymour, together.with storage in the mountain lakes, are being
considered together as the existing infrastructure allows for some
transfer between the two systems. The District intends to operate its
system in a manner that balances the drawdown of Capilano. and Seymour
Lakes so that their risk of shortfall is virtually equivalent at any
time. We will also maximize the use of Coquitlam water within the

constraints imposed by the transmission system.

It is proposed that one of the goals of the WSRP would be to identify
when the demand for water supplied from Seymour and Capilano rises to
the point where the reliability of staying above minimum allowable lake
levels through to the end of the drought is less than 99 percent (the
100-year drought case). This can be determined from the rule curve by
-entering with a known storage volume at a given date and determining
whether or not the previous week's average demand falls above or below
the reliability = 99 percent line. From this, it may be determined
whether or not action must be taken to reduce demand on the Capilano and
Seymour systems, and what relative reduction in demand is indicated for
the upcoming week. A set of weekly rule curves covering the entire peak
draw period is being prepared. At the beginning of each week an update
of the storage volume in Capilano-and Seymour together with the previous
week’s average withdrawal from those sources would be communicated to
the members by fa acsimile with a notation as to the perceived risk of
supply shortfall. If desired, a copy of the relevant rule curve could
also be provided, ‘showing the most recent storage/demand plot. The
change in risk of shortfall would be tracked in this manner and a_
recommended course of action would be ‘propos sed if the risk exceeds the

.

allowable.

Recommendation for Appropriate Response

In the simplest case, the District could use the rule curve to trigger
the usage of additional water from Coquitlam Lake in areas that would
otherwise be fed from Seymour or Capilano. As mentioned previously, the.
ability to do this during peak demand periods is limited by the supply

system's transfer capacity. Steps are being taken to improve this

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