TEMPERATURE

---

Prior to completion of Glen Canyon Dam in 1963, the temperature of water flowing through the Grand Canyon each year was highly variable, ranging from the icy, spring run-off to the warm, 85-degree summer-heated flows. However, once the dam was constructed, the temperature of the water released from the dam - drawn from the depths of Lake Powell and released through the dam's penstock intakes - ranged for many years between 45 and 50 F (7 to 10 C). With the lowering of Lake Powell, release temperatures have been increased to as high as 59 F (15 C) which has likely led to an increase in the humpback chub and other native fish populations in Grand Canyon. These increases in temperature, however, also increase the risk of expanding the distribution and abundance of cool/warm-water nonnative fish like brown trout, green sunfish, smallmouth bass, and walleye which could have a devastating impact on the humpback chub population in Grand Canyon like they have on humpback chub and other native fish populations in the Upper Basin.

---	---	---

Updates The timing of when releases are the warmest and when warm air temperatures have the greatest potential to warm the river has a large influence on downstream river temperatures. The warmest release temperatures occur in late October/early November but the greatest potential of warming the river in Grand Canyon occurs in July and September when air temperatures are the hottest. The reason is that it takes a lot longer to warm all the water in Lake Powell vs the water in the river as it flows downstream. Another thing to note that during the winter, river temperatures actually cool with distance downstream because releases are actually warmer than ambient air temperatures. Increasing Water Temperatures at the Little Colorado River Confluence (RM 61), 1990-2015

Links and Information Near Shore Ecology (NSE) Study of the fall steady flow test The Low Steady Summer Flow Experiment (LSSF) Page TCD Learning Page GCDAMP TCD Page Reclamation TCD Page Temperature Gages Colorado River at Lees Ferry Colorado River at 30 mile Colorado River above LCR Little Colorado River abv mouth nr Desert View, AZ Bright Angel Creek Colorado River abv Lava Canyon rm66 Colorado River bl rm127 Kanab Creek Havasu Creek Colorado River abv National Canyon Colorado River bl Diamond Creek Colorado River abv Spencer rm246 Papers and presentations 2013 Nearshore Temperature Findings for the Colorado River in Grand Canyon, Arizona—Possible Implications for Native Fish 2010 Selective withdrawal and sediment augmentation update Other Stuff