Open Space Advisory Board Agenda and Packet 2012 08 08

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• The native vegetative communities recommended in this plan evolved over thousands of years based on a snowmelt hydroperiod. They should respond well to a plan that creates similar hydrological conditions. • There will be some years that the reservoir will not be able to be filled to its maximum level; our approach using a natural hydroperiod will create vegetation zones that will have the resiliency to withstand such drought years, especially when compared to a vegetation plan that depends on a completely full reservoir. • Once vegetation is well established, larger drawdowns can be made every few years, as necessary, to help manage undesirable invasive species, such as bullfrogs or excessive cattails, or to perform other maintenance activities that may arise. Some important general guidelines are as follows: • These water levels, the recommended vegetation zones, and the recommended grading are all dependent on one another. • Our recommendations are based on the rehabilitated reservoir elevations and size shown in the 80% draft plan set and assume that the reservoir can have water year round. • Water management during the first couple of years after implementation of the plan will likely differ from these water management recommendations. It will be important to maintain relatively steady water levels to allow the plants to become well established. As a result, the City will probably need to avoid the maximum and minimum water levels during this time. • We do recommend some variation in the timing of water levels from year -to- year; it should not be exactly the same every year. • We recommend that the City monitor the site and adaptively manage water levels depending on the response of the vegetation and water quality. It is difficult to predict the vegetative response and water quality impacts to a high degree of accuracy. • During the hot summer months, the City should allow equal amounts of inflow and outflow to improve water quality in the reservoir. The exact amount of inflow /outflow would be determined after observing water quality parameters for a period of time following the commencement of reservoir operation. • Whenever the City adjusts the water level, it should be done slowly. Rapid changes are an unnatural condition and will likely overstress the vegetation. Figure 5 shows a draft conceptual cross section of the proposed water levels, grading of the reservoir side slopes, and corresponding plant communities. The water level management plan is to fill the reservoir to its maximum level of 5340 feet a couple of times in the spring, depending on growing conditions for that particular year. The first flooding, which is optional, would occur around late April to early May, and the second flooding would occur around late May to early June to