Wind, Currents, and Water Temperature


Analyses of seasonally averaged wind graphs indicated that winds over Upper Klamath Lake displayed diel patterns (Gartner and others, 2007). During the 2005 field season, minimum wind speeds occurred during late morning (about 1.75 m/s at 10:15 h at site MDN, about 3.0 m/s at 11:45 h at site HDB, and about 2.25 m/s at 12:15 h at site MDL); maximum wind speeds occurred during late evening (about 6.0 m/s at 20:45 h at site MDN, about 5.5 m/s at 19:45 h at site HDB, and about 6.5 m/s at 21:30 h at site MDL). [All times shown are referenced to Pacific Daylight Standard Time (PDST).] Upper Klamath Lake is a wind-driven system with little river inflow, thus horizontal water currents are expected to be a function of wind patterns.


Velocity measurements by ADCPs showed that a generally clockwise circulation pattern was established in Upper Klamath Lake under prevailing (northwest to north) wind conditions (Gartner and others, 2007; Wood and others, 2008). Although all ADCP records generally showed diel patterns in the water currents, the times of day of minimum and maximum current speeds were spatially variable in the lake because of the effects of bathymetry and geometry on water motion. The closest correspondence between times of maximum and minimum winds and maximum and minimum horizontal currents generally occurred at the southern end of the deep-water trench at site ADCP7. Maximum and minimum currents at site ADCP7 occurred within 1–2 hours of the corresponding wind events both near-surface and near-bottom. The largest offsets occurred in the middle of the lake at site ADCP6 (near MDL) where water currents led winds by 6–10 hours near-surface and by 2–6 hours near-bottom. Thus, even though water currents in the lake are wind-driven, the response of the water currents to the wind varies in timing and magnitude around the lake. 


Water temperature in the lake had a strong diel cycle, particularly near the surface. At times of maximum near-surface water temperature, the difference in water temperature between the near-surface and near-bottom of the water column was enough to provide resistance to mixing, particularly at the deepest sites in the trench. On most days, the water temperature difference was eroded in late evening or early morning by a combination of high winds and cool air temperatures (Wood and others, 2006; Hoilman and others, 2008). The ΔT° at sites MDT, MDN, and EPT were used to determine the seasonally averaged diel patterns (fig. 2). The maximum ΔT° was greatest at site MDT, the site closest to site ADCP1 and in the deepest water, and occurred there the latest in the day (19:00 h). The maximum ΔT° at site EPT, the closest to site ADCP5, was less than at site MDT and occurred at 18:00 h. The maximum ΔT° at site MDN, which was closest to site ADCP3 and in shallower water than sites EPT and MDT, was approximately the same magnitude as at site EPT but occurred earlier in the day at 16:00 h. Seasonally averaged diel patterns in ΔT° were not available near sites ADCP6 and ADCP7; values at site MDN were used when necessary for analyses because the water depths at sites ADCP6 and ADCP7 were similar to that at site MDN.


First posted March 16, 2011