Upper Lake Mary Watershed Monitoring Program
The Upper Lake Mary (ULM) Watershed Monitoring Program is funded through a collaboration of partners that include the City of Flagstaff, National Park Services, and the Coconino National Forest. The City was recently awarded a grant from the National Park Service to assemble a baseline hydrology report to summarize data collected under the program and data available within the watershed. This report was completed as a draft in July 2022, and is available here for download.
Upper Lake Mary (ULM) provides numerous services to Flagstaff residents including recreation and drinking water. On average, around 28% of the water produced for use comes from ULM (1949- 2022). Because the lake is primarily fed by precipitation and surface runoff, climate variability and change can influence lake levels, and consequently, this water supply source.
In 2019, Water Services consulted with the University of Arizona Climate Assessment for the Southwest (CLIMAS), to review how climate variables, including precipitation and temperature, have influenced water levels in Upper Lake Mary over the past 60 years. The primary questions addressed by the study include: Which climate factors are most important for explaining the variability in lake levels? How have the relationships between climate and lake levels changed over the 58-year study period? What are the effects of extreme climate years on lake levels? They also analyzed trends and changes in both ULM lake levels and the climate variables over time, and took a closer look at drought.
Upper Lake Mary: Lake Level Response to Climate VariabilityThroughout all analyses in this report, cool season (Nov-Mar) precipitation consistently plays the most important role in determining ULM lake levels. This emphasizes the primary influence of combined winter snow accumulation and early spring precipitation on lake levels for the upcoming summer. While this relationship holds for the entire ULM record, it does appear that temperatures are warmer for the low lake level years in the 2nd half (1989-2017) of the ULM record compared to 1st half (1960-1988). Because both precipitation and temperature influence snow accumulation and melt rates, the increase in surface temperatures over recent decades, as well as projected warming in the future, have important implications for the water cycle and surface water supply in the Flagstaff area. Warmer temperatures lead to less precipitation falling as snow and earlier spring melts, which drives shifts in peak runoff and supply. The significant increase in temperature could start to play a more important role in influencing ULM lake levels as seen in recent droughts in California and in streamflow records from the upper Colorado River basin. Specifically, the recent 2012-2014 drought in California was not dominated by unusually low precipitation, but rather extremely high temperatures. In the Upper Colorado River Basin, decreasing runoff efficiency has been documented since the 1980’s and has been attributed to increases in temperature. Despite the continued importance of Nov-Mar precipitation in the ULM area, these changes in temperature have the potential to enhance the risk of decreased water supply in the future.
While surface water production is relatively highly correlated with lake level minimums, understanding the characteristics of drought events could provide additional information for supply planning. The study also indicated that the severity of a drought event not only depends on the length but also the intensity of the drought in each individual year and the cumulative departures. The two most recent drought events lasting at least three years have temperatures above the 70th percentile, again highlighting the potential emergent role of warming temperatures.
The 2020 CLIMAS report titled Upper Lake Mary: Lake Level Response to Climate Variability can be downloaded here.
Flowtography(c) & "Watching Our Watershed"
In 2015, the Water Services Division partnered with the Salt River Project (SRP) to provide ongoing operations, maintenance, and data collection for six Flowtography(c) sites within the 4FRI (Four Forests Restoration Initiative) area of the Upper Lake Mary Watershed. The six sites were installed in November 2014. Two additional sites were installed in April 2017 at the Newman Canyon USGS gage site and Upper Lake Mary watershed 2B. Flowtography uses a game camera mounted in a tree to take one photo every 15 minutes of a graduated rebar stake in the center of a channel. The channel has been surveyed for slope, cross-sectional area, and roughness such that flow can be calculated using the Manning’s equation. The height of water on the streamflow gage is recorded from photographs taken during flow events. Each site is also equipped with a pressure transducer. The streamflow flow data will serve as a baseline for comparison with data collected after forest treatments. These data are important for informing watershed treatment and maintenance of the forests for maximum runoff into Upper Lake Mary and groundwater recharge to the aquifer.
Learn how Flagstaff uses Flowtography to preserve our water supply.
Time Lapse Videos of Monitoring Sites
The Water Services Division and two partnering agencies — the Flagstaff Watershed Protection Plan Project and the Lake Mary Walnut Canyon Technical Advisory Committee — partnered with the U.S. Geological Survey to install a streamflow gage and sediment sampler in Newman Canyon in 2014. Newman Canyon is the largest single contributing tributary to Upper Lake Mary. The image above displays the sub-watersheds of the Walnut Creek Watershed, watersheds that are part of the Upper Lake Mary Watershed Monitoring Program and NAU Paired Watershed Study, and the location of the USGS Newman Canyon Gage and Sediment Sampler