1. First, could you quickly introduce yourself?
Yes, my name is Jord Gertson, I have worked as a hydrologist in the Upper Arkansas River Basin for 25 years. My efforts have focused on water resource management for the Upper Arkansas Water Conservancy District, CERCLA investigations for the USEPA and Water Quality compliance requirements established by Colorado Department of Public Health and Environment.
2. To start, what do you want the general public to know about water management decisions within the Upper Ark?
Water management decisions are very complex, they are limited by legal constraints and available supply. Where rapid changes in supply are typically relayed via “Real-Time” data. The uncertainties related to the collection of “Real Time” data are significant. Many people tend to think they can take “Real-Time” measurements for gospel, but this data should be viewed with caution, as there are various sources of uncertainty. Our goal is to estimate discharge within 5% of actual conditions as kind of a “maximum error”, but onsite conditions can change quickly and regression analyses can be off by 20% or more.
During the rising limb of the snow melt hydrograph there’s significant stream channel morphology and accumulation of debris especially during peak flow. This means that you can have variations in discharge that aren’t represented properly through the “Real-Time” data collection process.
For an example from last month, if you look at the Wellsville stream gage data, at the end of June and beginning of July, flows started to drop off really quickly- we had an above average peak flow and then flows were quickly below average. Entities that operate the Voluntary Flow Management Program (VFMP) were watching the “Real-Time” stream-flow data closely to make decisions on releases to satisfy the target flow of >700 CFS at Wellsville. On the 12th of July additional releases were made from Clear Creek to supplement streamflow at Wellsville. The projected “Real-Time” discharge data indicated flows were near the target minimum. Efforts had begun to make releases to satisfy conditions outlined in the VFMP. Yet, on July 18th, The division of water resources calibrated “Real-Time” flow data at the Wellsville stream gage with a physical measurements and discovered that it was not running 730 CFS, it’s actually running about 900 CFS.
There can be lots of different mechanisms for error when calculating stream flow from a river stage or height measurement.
3. As a boater, how should someone make safe decisions when those inaccuracies are inherent to the reported figures?
If you’re wanting to get on the river at a specific flow, say 1,800 CFS but 2,000 CFS is beyond your ability, you should look at trends–are we trending down? Are we trending up? to make sure you don’t reach that threshold where you feel unsafe.
4. As a water manager, how do you correct for these uncertainties?
In the water management world, we make decisions based on the “Real-Time” data, we have to consider that this is the best information that we have at the time. It can be difficult, we’re trying to predict when we can make live stream exchanges, when we should make releases from storage, when we should try to fill reservoirs, or trade water. Timing is very important. We are required to factor in weather predictions that directly relate to streamflow to meet certain thresholds. We end up factoring a comfort buffer to be certain that thresholds are not exceeded.
5. How does water management on the Upper Ark differ from the rest of the basin and the state of Colorado?
The Arkansas River Basin is the largest watershed in Colorado with the least amount of water. We are forced to maximize the use of the water we have. The supply for most of the basin relies on the orographic effects of the mountains to collect and store water from winter storms in the form of snow. Significant water projects have been implemented to balance the basin’s demand and supply for water. Entities that export water from neighboring watersheds through the Upper Basin rely on the native stream systems and a vast infrastructure to provide water for a multitude of beneficial uses in Colorado.
6. As a hydrologist in the Upper Ark, what are the decisions you’re making and how are you making them?
When making replacements for out of priority depletions it’s important to note that everything that controls our decisions begins with the stream call. We look at the active stream call multiple times per day, and then also look at streamflow trends and weather forecasts to predict changes in the stream call.
Right now I’m keeping a close eye on Cottonwood Creek, anticipating a local call on Cottonwood Creek. It’s actually been a pretty good melt season, meaning that we’re not on a local call yet, but that local stream call is going to happen. When the local call comes on it will change our decisions on how we make releases for those out of priority depletions.
Right now the Arkansas stream call is March 1st, 1887, so anybody that is using water post that date is out of priority. We are required by court decree to make out of priority depletion replacements in time, location, amount, and quality. It’s important to be able to predict when and where we can store water and when we’re going to have to start releasing from other locations to satisfy the stream call.
At this point in time, our Trans Mountain imports into the Upper Basin are about 52 acre-feet per day, and exports at Otero Pump Station are 178 acre-feet per day from the Upper Basin.
7. Where are those imports coming in and where are those exports leaving from?
Water exported upstream of Pueblo Reservoir occurs mostly at the Otero Pump Station from Twin Lakes Reservoir. Imports into the Arkansas River Basin occur at Columbine Ditch, the Ewing Ditch, Wirtz Ditch, Homestead Tunnel, Charles Boustead Tunnel, Busk Ivanhoe Tunnel, Twin Lakes Tunnel, and the Larkspur Ditch.
8. Since this is the July River Report, what has happened in July that you would like to ensure that the public understands?
Probably implementation of the Voluntary Flow Management Program using “Real-Time” data. The Board of Water Works Pueblo and USBR do a really good job stepping up to that program. They are often try to extend it past the August 15th date, and they have been successful at that voluntary effort over the past several years. During low flow periods, they make every effort to extend that as much as they can by making releases from Clear Creek or Twin Lakes. Communication and cooperation among the USBR and the water users is essential to make this happen.
9. Looking forward to August and the next three months, what are you paying attention to for the rest of this summer and early fall?
I am paying close attention to “Real-Time” data collected on Grape Creek, the South Arkansas River and Cottonwood Creek. Stream calls on those tributaries restrict water substitutions to make replacements, so instead of using Pueblo Reservoir we have to use upstream water rights to make those replacements above the calling water right. We’re closely monitoring the “Real-Time” flows and stream calls within all the major tributaries of the Upper Arkansas to avoid causing injury to the calling water right.
Monitoring these tributaries begins with the water commissioner, where communication is essential. They’re delivering water rights to entities, they’re managing a multitude of ditches and changes in supply. They really have all the insight to what’s going on and have a really good handle on predicting what’s going to happen.
I also look back in time to understand, historically, how much rain did we really get, how variable was it, what was the associated streamflow responses, where is the rainfall occurring now, where it’s not and where water deliveries need to be made to make the calling water right. So yeah, it’s a combination of many things.