Thermal Dynamics of Lake Powell and its Inflow: Patterns during the LSSF Experiment and Beyond Grand Canyon Monitoring and Research Center Susan Hueftle Grand Canyon Monitoring and Research Center Susan Hueftle

TidBiT Study Findings –LSSF hydrograph Effects Seiche Effects –Inflow Dynamics –Model Calibration Monitoring Findings –Hydrograph summary –3 rd Year of lake underflow –Near Mixing of Lake PEP Results TidBiT Study Findings –LSSF hydrograph Effects Seiche Effects –Inflow Dynamics –Model Calibration Monitoring Findings –Hydrograph summary –3 rd Year of lake underflow –Near Mixing of Lake PEP ResultsOverview:Overview:

TidBiT® thermistors –Sensitivity ± 0.08°C –Resolution from –4 to +37°C –Sealed in epoxy, good to any depth –Infrared download to 32 Kb –15’ interval readings for 11 months –Purchased 66 for $91 each –Demonic intrusion 4 downlake stations Sheep/Cataract Canyon inflow Hourly Met data from Page: –Mean wind speed –Wind gusts –Air temperature GCD data from B. Vernieu TidBiT® thermistors –Sensitivity ± 0.08°C –Resolution from –4 to +37°C –Sealed in epoxy, good to any depth –Infrared download to 32 Kb –15’ interval readings for 11 months –Purchased 66 for $91 each –Demonic intrusion 4 downlake stations Sheep/Cataract Canyon inflow Hourly Met data from Page: –Mean wind speed –Wind gusts –Air temperature GCD data from B. Vernieu TidBiT Experiment

Deployment Problems Tampering decreased with distance from dam Water, rust Lake action, houseboats Deployment Problems Tampering decreased with distance from dam Water, rust Lake action, houseboats Wahweap: May ‘00-present discontinuous Padre bay May-June ’00 Padre bay May-June ’00 Escalante May-July ‘00 Escalante May-July ‘00 Oak Aug ‘00-Mar ‘01 Oak Aug ‘00-Mar ‘01 Sheep May ‘00-present Sheep May ‘00-present San Juan Inflow Mar 01-present San Juan Inflow Mar 01-present Tidbit Deployments

Padre tidbit recovery Initial boat-buoy interface Comes to rest on shore Returns to Bosom of GCMRC lab Recovery room NPS water lab NPS retrieves buoy & tidbits, Ride around in cart for 2 days Happily sampling Away on station Houseboaters struggle with moral & practical dilemma of restoring tidbits to original position

TidBiT Study Findings : Seiche effects A Seiche is a submarine oscillation of lake strata caused by external disturbances. Seiching increases dispersive and mixing of strata, particularly in the hypolimnion. It can create short-term oscillations in water quality parameters in dam discharges; and create a trace for detecting downstream flow velocities and mixing. Seiche typically followed wind event 3-12 hours Seiche period average 3-6 hours, up to half day Displacement greater at surface Signature from dam was insufficient to override any wind seiching A weakness of the experiment was the degree of homogeneity in the lake during the study Wahweap oscillations noisier than uplake stations A Seiche is a submarine oscillation of lake strata caused by external disturbances. Seiching increases dispersive and mixing of strata, particularly in the hypolimnion. It can create short-term oscillations in water quality parameters in dam discharges; and create a trace for detecting downstream flow velocities and mixing. Seiche typically followed wind event 3-12 hours Seiche period average 3-6 hours, up to half day Displacement greater at surface Signature from dam was insufficient to override any wind seiching A weakness of the experiment was the degree of homogeneity in the lake during the study Wahweap oscillations noisier than uplake stations Wahweap Oak

TidBiT Study Findings : Inflow Dynamics Inflows respond to temperature changes faster than the down-lake Both response to the same weather patterns Inflow conditions are critical for a well-calibrated model, lake levels can influence Sheep canyon Inflows respond to temperature changes faster than the down-lake Both response to the same weather patterns Inflow conditions are critical for a well-calibrated model, lake levels can influence Sheep canyon

TidBiT Study Findings : Inflow Dynamics Inflows responses faster to temperature changes than the lake Both response to the same weather patterns Inflow conditions are critical for a well-calibrated model, lake levels can influence Sheep canyon Inflows responses faster to temperature changes than the lake Both response to the same weather patterns Inflow conditions are critical for a well-calibrated model, lake levels can influence Sheep canyon

Peaks every year between late January and mid- February Decreasing salinity and increasing temps in the lake have reduced vertical density gradients Bottom strata becomes unstable and is subject to mixing Mixing could introduce higher concentrations of nutrients and other components to water column Peaks every year between late January and mid- February Decreasing salinity and increasing temps in the lake have reduced vertical density gradients Bottom strata becomes unstable and is subject to mixing Mixing could introduce higher concentrations of nutrients and other components to water column TidBiT Study Findings : Winter Mixing

Wind Air Temp Q cfs Water temps 1-80 m Water temps 1-80 m

Peaks every year between late January and mid- February Decreasing salinity and increasing temps in the lake have reduced vertical density gradients Bottom strata becomes unstable and is subject to mixing Mixing could introduce higher concentrations of nutrients and other components to water column Peaks every year between late January and mid- February Decreasing salinity and increasing temps in the lake have reduced vertical density gradients Bottom strata becomes unstable and is subject to mixing Mixing could introduce higher concentrations of nutrients and other components to water column TidBiT Study Findings : Winter Mixing Detail: Jan- Apr 01 Wind Air Temp Bottom water temps m Bottom water temps m Q cfs

Wahweap forebay, Sept 1990 to Apr 2001 Most thermally mixed: Feb ’73, Jan ’91 come close Underflow evident Most thermally mixed: Feb ’73, Jan ’91 come close Underflow evident

Lake Findings: December 2000 Low hydrograph of 2000 produces more saline conditions Antecedent conditions relatively dilute & mixed Low hydrograph of 2000 produces more saline conditions Antecedent conditions relatively dilute & mixed

Lake Findings: March 2001 Third year of winter DO underflow Thermally nearly homogeneous Third year of winter DO underflow Thermally nearly homogeneous

Conclusions: TidBiT inflow/stratification data critical input for future modeling efforts Current TidBiT results track winter mixing –hypolimnetic mixing unprecedented in the lake’s history –Only approached <1°C 2 other years: 1991 & 1973 –Hypolimnetic mixing could introduce higher concentrations of nutrients, other ions to dam withdrawals Seiche effects dominated by wind, no detectable signature from dam operations Seiche signature greatest in open bays, oscillation seen from downstream to upstream 3 rd Year of lake underflow and hypolimnetic oxygenation TidBiT inflow/stratification data critical input for future modeling efforts Current TidBiT results track winter mixing –hypolimnetic mixing unprecedented in the lake’s history –Only approached <1°C 2 other years: 1991 & 1973 –Hypolimnetic mixing could introduce higher concentrations of nutrients, other ions to dam withdrawals Seiche effects dominated by wind, no detectable signature from dam operations Seiche signature greatest in open bays, oscillation seen from downstream to upstream 3 rd Year of lake underflow and hypolimnetic oxygenation