This application can be used several ways. First, you can navigate to different pages using the bar on the top of the page. Click on Interactive map to return to the main page. On the interactive map, you can click on any of the circles to bring up a popup detailing information on that specific reservoir. You can see the current reservoir level and the name of the reservoir, notice the color of the circle corresponds with the current reservoir level. You can zoom in on the map to see what reservoirs are near you. There is also a dropdown menu on the right side of the screen where you can choose specific reservoirs. Below this is a graph that by default shows the average (mean) reservoir levels across the state. This graph will change depending on the reservoir you have selected. The graph also shows the median reservoir level and the previous year's value. This is useful for comparing to the previous year and what would be considered normal for that reservoir given the recorded history. Below the graph are two buttons. One to download the map, this will provide you with a figure labeling the reservoir and its current capacity similar to the one on the screen. The second button is to download the plot that you have selected.
The data used to compile this dataset come from multiple sources and the division does not verify the accuracy of these sources. The (Median), (Previous), and (Current) lines on the graph show the capacity for the first of each month. However, the most recent value of the (Current) line is updated daily. In some cases, the most recent (Current) data point represents today, other times the first of the month, and sometimes the previous months capacity is carried over. To understand where the data comes from and the exact date represented, please download the csv file from theStats
page and inspect the source and date columns.
A median is one way to calculate an average and is used to help explain what a normal value for a given variable is. In this case, we want to know what is the normal reservoir level (value) for a reservoir. To do this we take 30 years (1991-2021) of reservoir levels and take the middle value of the population. This gives us a good idea of what a normal reservoir level is by using past data.Four reservoirs did not have data going back to 1991, and medians were calculated starting from 2011. These reservoirs include Cleavland, Miller Flat, Sand Hollow, and Big Sand Wash. Strawberry had its capacity increased in 1998, so data previous to 1998 was not used for its median.
Reservoirs hold and store water for agriculture, drinking water, and other uses. Utah's water supply largely comes from our snowpack and precipitation during the winter. In the spring, this snowpack melts and starts flowing downstream. Without reservoirs, this snowmelt would largely be gone by the early summer, and flood events would be more common. With reservoirs, we can store water and extend our water supply throughout the year. This way we can continue agricultural production into the late summer and fall, and provide water to our public. Still the reservoirs can only give us so much of a buffer to the natural system, so in times of drought it is good to know where your water comes from and the condition of the reservoirs. Sometimes we may have to cut back our own water use to help refill or maintain our reservoirs.
Is it late Summer or Fall and the reservoirs seem low? These are normal times for reservoirs to be low and a red dot on the map does not mean it is bad. We fill up our reservoirs in the spring and slowly deplete them throughout the year. Did the graph show an uptick when you did not expect one? Think back to this year's weather events, maybe the trend can be explained.
To understand if a reservoir is below normal or above normal, compare this year's line in the plot to the median line. Notice the trends in the data and think about this year's past winter, snowmelt, or how much rain your area got during a given month. For a quick look, check out theStats
page which shows reservoir conditions throughout the state and by hydrologic basin. The stats page also shows you the percentage the reservoir levels have deviated from the median. A negative value may indicate times are drier than normal.
A common question is how a storm may have impacted reservoir levels or drought conditions. Generally, a single storm event or even a month of storms have minimal impacts on these longer-term conditions. Smaller reservoirs will be impacted first, but larger reservoirs that store multiple years worth of water will take many events to begin seeing an impact. Look at the graphs to see if you notice an uptick related to these events you have questions for. If the graphs show that this year's reservoir level is coming closer to the median storage, maybe the events are having an impact. Rain also means fewer people are irrigating their crops and lawns, everything helps.
Some reservoirs do not have as much water in them compared to others and may be drained more quickly. For example, larger reservoirs store several years of water. Strawberry can store 7-10 years when full and Starvation can store 3-4 years. Smaller reservoirs may be designed to even out water delivery and only store about a year's worth of water. Some reservoirs also supply water to more people or are in a drier or wetter area of the state. There are many reasons why some reservoirs maintain a higher fill than others. You may need to research more specifics on the reservoir to find out why.
You may notice a reservoir's maximum capacity change on occasion within this dataset. This is because organizations use different methods of calculating reservoir storage capacity. Some organizations use the total (design) capacity in the reservoir, while others exclude volume that cannot be used. For example, water that is below the release point (dead pool) or held in store for fish and other aquatic life may not be included in the total reservoir capacity. Since much of this data is communicated as percentages, it is important to compare the reservoir's current capacity to the full capacity the specific source uses.