MIKE LAMAR - CE394K
Comparison of Snow and Stream Data
Snowmelt into mountain streams is the largest source of water for many areas in the Rocky Mountain region. Roughly 80% of Colorado's annual water supply comes from snowmelt [1]. Unfortunately, snowmelt values vary greatly from year to year. In the extreme cases, at the Utah border Colorado River flows were 960 cubic feet per second (cfs) in 1956 and 69,800 cfs in 1984. Not only is snowmelt dependent on the snowpack levels, other factors such as soil moisture content, temperature and precipitation play major roles. Due to the high variability in snowmelt from year to year, mountain states must be able to predict what the snowmelt levels will be months in advance.
Snowmelt also plays a role in water pollution issues. Recently, in Summit County, the ski resort Arapahoe Basin planned to use its water rights to produce artificial snow in order to stay open year round. A Basin owns water rights on the Snake River, where discharges from the abandoned Pennsylvania Mine flow to. This abandoned mine is leaching heavy metals into another tributary to the Snake River. Although the ski resort has the rights to remove water from the river, environmental agencies have claimed that extracting water from the Snake will reduce the amount of uncontaminated water available to dilute the heavy metals from the mine. This degradation of the overall stream quality is a violation of the Clean Water Act, according to Colorado Wild. [2].
An estimated 22,000 abandoned mines exist in Colorado today [3]. Figure 1 below shows the mines in Summit County. Pollution of rivers in Summit County is closely monitored, because most streams flow into the Dillon Reservoir, which is a main source of water for Denver. It is likely that the Arapahoe Basin case is the beginning of more to come, with population densities spreading out into mountain regions. The use of snowpack/snowmelt data can be valuable in predicting which years water can be extracted or when the streams will be too polluted. GIS can be used to assist in this prediction.
Figure 1 - Mine Distribution in Summit County
In order to fully understand how snowpack and stream discharge levels are related, GIS can be a powerful tool. By mapping all of the snowpack and discharge data, one can roughly correlate what stream the snowpack in that area melts to. In the future years, snowpack data (including soil moisture content, temperature, precipitation, snow water content) can be used to "forecast" the stream discharge levels later in the year, after the snow melts. Although powerful models are built to overcome many pitfalls in this prediction, the scope of this project is limited to using GIS as a tool to visually aid where each SNOTEL site and stream gage is positioned. This analysis will focus on Summit County, Colorado. The Snake River has a SNOTEL site directly upstream from a stream gage, and these two sites will be compared.
In order to understand the region, first a map of Colorado and the Continental Divide was obtained. Next, a county map shows where Summit County lies in relation to the Continental Divide. Figure 2 shows Summit County in relation to Denver and the Continental Divide.
Figure 2 - Map of Colorado
Summit County lies directly west of the Continental Divide, and its southeast border is the Continental Divide itself. Next, the river coverages in the region were obtained from the NHD website. The borders of Summit County are the same for the Blue Watershed, which is the easternmost part of HUC Region 14 (Upper Colorado Basin). The Blue Watershed is in HUC Code 14010002. Figure 3 shows the rivers and lakes/reservoirs in Summit County. The Snake River is highlighted in red.
Figure 3 - Rivers in Summit County
Once the location of the Snake River was found, SNOTEL survey points were obtained from NOHRSC. SNOTEL sites are automatic snowpack sensing and data transmission sites where critical information is obtained. By placing these SNOTEL points over the previous map, SNOTEL sites of interest were found. In Figure 4, the easternmost SNOTEL (Grizzly Peak) point (red dot) was found on a tributary of the Snake River. The only stream gage on the Snake River is shown in black, downstream of the SNOTEL point. In this case, it is fortunate that the runoff from this area will directly correlate to the stream gage data downstream because there are no other streams nearby the SNOTEL point. This may not be the case in some circumstances, and a more in depth analysis of runoff directions would have to be done.
Figure 4 - SNOTEL Survey Points
The SNOTEL and stream gage data was then taken from the Natural Resources Conservation Service and USGS, respectively. The data was provided in text format, and they were plotted in Microsoft Excel.
Once it was determined which SNOTEL and stream gage sites to use, the data was collected for October 1995-September 1999. From the SNOTEL site, snow water content and precipitation data were both obtained. A direct comparison of the snowpack (or snow water content) and stream discharge data show some similarities, but also some differences. It does show that the stream discharge levels increase within days of the steep drop in snow water content values. This shows two trends, as shown in Figure 5. First, the stream discharge levels are highly dependent on snowmelt, as discussed above. Second, the snowmelt from Grizzly Peak SNOTEL site flows past the Snake River gage station. What this figure does not show, however, is that higher snow water content (SWC) levels do not always produce higher stream discharge level. For example, in 1996, the SWC levels were higher than 1997, but the discharge values show opposite trends. The same applies with 1998 and 1999.
Figure 5 - SNOTEL and Dishcarge Data for Snake River
Once it was determined that the snowpack (SWC) data did not predict the stream discharge levels accurately, the precipitation levels were analyzed and compared with discharge values. The precipitation data seems to compare better with the discharge levels. As shown in Figure 6, in 1996 and 1997, precipitation levels are high, and the discharge values are also high. In 1998, the precipitation levels fell significantly, and the discharge levels for that year decreased significantly as well. It should be noted that although the precipitation levels are much greater for 1996 than 1997 after June, the discharge levels are highly dependent on snowmelt, not rainfall. Most of the snowmelt occurs before July, as seen in Figure 5.
Figure 6 - Precipitation and Discharge Data for Snake River
Snowmelt plays an important role in water quantity issues. In Summit County the snow melts straight into the mouths of Denver. The Denver citizens are concerned with both the quality and quantity of water they will receive each year, and predictions of water levels due to snowmelt is extremely helpful. Also, water level predictions can be used to regulate how much water can be removed from streams that are polluted, like the Snake River, to ensure that the pollution levels do not reach unacceptable levels. .
GIS is a useful tool for visually connecting SNOTEL sites and stream gage data. Once the correct sites can be determined, it is also useful to store the data that is found from SNOTEL survey sites, such as temperature, snow water content, precipitation and soil moisture content.
Although the snow water content values do show good comparison with the stream discharge values, it seems that its use as a predictive tool alone is insufficient. Other variables such as precipitation must be analyzed to better predict changes in discharge levels.
The next step in this project is to use all of the variables to determine the river discharge levels more accurately. This has been done in the past by the Army Corps of Engineers and certain international organizations (Canada and Sweden). Unfortunately, in order for these models to work adequately, assumptions must be made based on the regional area. Therefore, models are very region specific right now, due to difference in snow density, precipitation, etc.
"Colorado at a Glance", CRWUA; http://crwua.mwd.dst.ca.us/co/crwua_co.htm
Lipscher, Steve, "Colorado ski area fights to use river water to make snow"; The Denver Post, 10/7/2000
Peckham, Scott D., "Polluted Streams Near Colorado Ski Resorts: A Preliminary Study Using RiverTools"; http://www.rsinc.com/AppProfile/riv_hy_casestudy.cfm
