Managing the Reservoir for Drought Security Rather than to Satisfy Growth
Loch Lomond Reservoir is the City’s water “savings account”. When Santa Cruz residents conserve water in the dry season, there is more water stored in case of a dry winter. A good example was 2009, a dry year. On account of our conservation efforts, Loch Lomond was 90% full at the end of the dry season, Oct 1. That’s an ideal level for the lake in case of a second dry year, because a minimum of winter rainfall would refill the lake. Current City policy allows the lake to dip well below the optimum level at the end of a normal year dry season. (If the reservoir is expected to be above 64% on October 1, the City takes no action to curtail summer use). Our current policy gambles that the reservoir will re-fill during the winter months. But in three out of ten winters, that’s not the case.
Current policy is to use reservoir water to satisfy growth in water demand. Managing the reservoir for optimal drought security would require an end to growth in water demand, since Loch Lomond is the only water source not fully tapped for peak-season use. According to the City’s Adequacy of Municipal Water Supplies to Support Development (2004), “Any future increase in seasonal or annual demand for water will be felt through greater and greater withdrawals from Loch Lomond reservoir.”2
The City could offset new growth with conservation improvements in existing development. The Soquel Creek Water District already has a water-neutral development policy. Builders need to offset 120% of new water demand by installing water efficient toilets in existing buildings. When the potential of toilet retrofits is exhausted, there is a great deal of untapped potential in replacement of landscapes.
With a modest curtailment in normal year summer consumption, withdrawals from the reservoir could be limited to an ideal level. For example, a lake capacity of 85% on Oct 1 of each normal year would have 500+ million gallons of water more than the City’s current target of 64% capacity. That would ensure that during the second year of a drought, the City would have more water available than the 450 million gallons expected from a desalination plant. Recent years have shown that this target is reasonable. On Oct 1, 2008, the reservoir was at 84% capacity. In 2009, a dry year, the reservoir was at 90% on Oct 1. And in a repeat performance, Santa Cruz customers conserved their way to a lake level of over 90% in 2010.