Water Temperature Management in River Restoration Tom Dunne River Restoration Spring 2010 Concerns about stream temperature Metabolism Food requirements, appetite, and digestion rates Growth rates Developmental rates of embryos and alevins Timing of life-history events, including adult migrations, fry emergence, and smoltification Disease-host and parasite-host relationships Oxygen solubility-temperature relationship Limits of viability Constriction of a species range by dams can confine a cold water fish to warm lowland rivers Whole Columbia R. is temperature-impaired because of reservoir storage Water temperatures, T, governed by the net heat load, Q (J) Non-point heat load Point loads of heat: Chattahoochee R. passing waste treatment plants, Atlanta Complicating effects of stratification in large reservoirs Some large dams fitted (sometimes retroactively) with valves to release water from various depths for downstream temperature control Typical chain of events in setting temperature standards Grab samples or automated monitoring water temperatures exceed by > 5 o F 74% of time EPA guidance for assessing beneficial use impairment temperature (or other pollutant) standard exceeded >25% of time assessed as "not attaining. Water contaminant sources or physical alteration of the stream shall not raise or lower the water temperature more than 5 o F [2.8 o C], or contribute to a stream temperature in excess of 90 o F [32 o C]. May be a thermal mixing zone below a point source in large rivers If out of compliance, need to develop a strategy for reducing temperatures --- usually requires some predictive model to assess options and their effectiveness. Surprising amount of data available, but also easy to collect Implementation of a (temperature) TMDL E.g. N. Ponil Creek, Canadian R basin, New Mexico 1. Channel widening (increased width to depth ratios) increases the stream surface area exposed to incident solar radiation 2. Riparian vegetation disturbance reduces stream surface shading, riparian vegetation height and density, 3. Reduced summertime base flows. Base flows are maintained with a functioning riparian system so that loss of riparian will lower and sometimes eliminate base flows. Need a mathematical model; many available from agencies and web Eeek! Thermal energy balance of water in a stream reach in a time interval, t w stream width (m) Q change in heat J L reach length (m) t time Q n net radiation (Wm -2 ) Q h sensible heat (Wm -2 ) Q e latent heat (Wm -2 ) Q b heat flow through bed (Wm -2 ) Q f heat from friction (Wm -2 ) Q gw heat from groundwater (Wm -2 ) Q trib heat from tributaries (Wm -2 ) Hydrological controls on thermal energy balance of water in a stream reach Small stream reach in Scotland during spawning season (Oct-April)? Large river in Central Valley of California in summer? Basis of summer-long conflict and negotiation between reservoir managers, fish biologists, and environmental water managers. Real-time management as well as longer-term planning Other controls are a matter of long-term planning or environmental assessment (e.g. channel widening risk after timber harvest) F w = F up + F trib + F lateral + F disposal Effectiveness of riparian shade for various channel widths Navarro R. TMDL, US EPA Hydrological features affecting F w confluence of tributaries groundwater inflows channel morphology (particularly conditions that create isolated pools or segments) springs, wetlands, water withdrawals, effluent discharges, and other hydrologic factors beaver ponds and other impoundments Environmental and manageable controls on thermal energy balance of water in a stream reach Q = t w L[Q n + Q h + Q e + Q b + Q f + Q gw + Q trib ] Q b seasonal heat storage below bed in absence of hyporheic flow; seasonal except in hydrothermal regions Q gw magnitude and temperature of hyporheic flow from riparian aquifer or bedrock joints Q trib magnitude and temperature of tributary inflows All riparian environment or management SNTEMP Stream Network Temperature Model (USGS website) predictions BasinTemp (Stillwater Sciences) Couples a solar radiation model, simple energy balance and hydrologic model, to calculate (1) the mass transfer of heat between each reach and the environment (2) the downstream transport of heat. Fit optimized to a few stations measuring T and Q