What we do
Instream flow studies
Instream flow studies combine biology and hydrology by examining the relationship between streamflow and aquatic habitat in local creeks. This is useful for determining how much water is needed to support fish and other aquatic organisms during different times of the year. By measuring streamflow at several local sites with automated streamgages throughout the year, we are able to determine whether fish in these creeks have sufficient water to spawn and grow.
Methods
The RCD has conducted an instream flow study of Carneros Creek using computer software called the Physical Habitat Simulation (PHABSIM) model. We will begin a flow study of Milliken Creek in winter 2009 using the same approach. The PHABSIM model allows us to collect measurements at several flows and interpolate habitat quantity and quality over a range of flows to identify critical flow thresholds for fish. The general approach we take is as follows:
- RCD biologists conduct habitat surveys to determine the quality and distribution of available habitat within a given stream.
- Once mapped, the habitat data are used to select a study reach based on physical, hydrologic, and logistical factors.
- Channel cross-sections are surveyed in several locations throughout the study reach in representative habitat units.
- A series of water velocity and water surface elevation measurements are made at each cross section at various target flows.
- A PHABSIM model is constructed using survey data and habitat suitability curves and then calibrated with known discharge/flow measurements.
- The model generates weighted usable area estimates for a given species and lifestage, which are then interpreted by biologists to identify flow thresholds for fish.
PHABSIM Models
- Water for Fish and Farms – Carneros Creek PHABSIM model, 2008
- Milliken Creek Flow Study – in progress
