Researching Flow Predictions for Your Upcoming River Trip

When you’re filling out your permit lottery applications, daydreaming about long summer days and clear starry nights, it can be hard to imagine what the river might look like. That’s why you need to know how to come up with river flow predictions. Not only can you attempt to avoid too-low flows and long days of frustration dragging boats off rocks, it’s important to avoid times when the river might be too high and beyond your skill set. Understanding the water level during your target timeframe is an essential part of river trip planning.

*Scouting Zoom Flume rapid on the Arkansas River in Browns Canyon (left) on June 1, 2014, and the flow data on the right showing that it was running a little over 3,500 cfs*

Resources for river flows

For the big Western multi-day trips that require permit lottery applications months in advance, there are two major resources I use: American Whitewater and USGS Water Data. I use American Whitewater to figure out what gauge I should be using. For example, the American Whitewater page for Deso indicates that the gauge to use is Green River at Green River, Utah.

Example flow data from Green River, Utah — *The American Whitewater river flow page for the Green River through Desolation and Gray Canyons, indicating the name of the gauge.*

The main American Whitewater page also provides a recommended range of flows for running the river. If the flow is too high a week out from put-in day, no matter how long the trip has been planned, I think long and hard about canceling the trip. High-water trips require strict attention to on-river safety, and offer the threat of fewer campsites and colder, scarier water. Conversely, if the level is too low, the trip could be a slog of long rowing days and repeated attempts to lift boats off rocks.

The American Whitewater flow page will give you the current flow, but if you’re planning a trip for July, the flow in January isn’t all that useful. That’s where the USGS data comes in.

Finding the river flow prediction for a specific time range

To find the predicted flow for a stretch for a specific time range, you first need to find the data for the correct gauge. To get the correct gauge, you can either use the link given by American Whitewater (on the right in the screenshot above), or use the gauge name given by American Whitewater to search on the USGS site.

From the main USGS site, click “Build Time Series.” Select the button for “Site Name” on the next page.

*Selecting time series for river flow predictions*

Type in the gauge name.

Selecting river sites in researching predicted flows — *Choosing the site name for river data*

Scroll down to choose the output format.

River data output format selection — *Choosing output format for river flow information*

On the next screen, scroll through the table to find the correct gauge.

List of river gauges — *Finding the correct river gauge*

When you get to the gauge page, you can choose to make a graph with stats. I like to look at the previous year, so I can see how the river level moves up and down seasonally. You can see in the screenshot below that I set the date range to February 1, 2019 through December 31, 2019.

River flow data — *Selecting criteria for a river flower graph*

Click go, and the site will redirect you if you’ve chosen to see data older than 120 days. Then it will load in a new tab. Your graph will look something like this:

*Example hydrograph from the Green River, showing discharge data for 2019*

The blue line is the actual data from 2019, showing the discharge measured throughout the year. The yellow symbols are the median daily statistic from all the available data for the gauge. The discharge is shown on a logarithmic scale: each horizontal line from 1,000 to 10,000 represents an increase of 1,000 cubic feet per second (cfs), while each line above 10,000 cfs represents an increase of 10,000 cfs. By looking at the blue line, you can see that in 2019, the discharge peaked at nearly 30,000 cfs. The yellow symbols indicate that, in general, the discharge usually peaks around 18,000 cfs. So there was slightly more flow in 2019 than usual.

Looking at the dates on the bottom, you can see that the peak flow usually occurs around June 1. If I were planning a family float, I would plan to go later in the summer, around the middle of July, when the flow is usually a much more reasonable 5,000 cfs. There are still hazards associated with lower flows, but you can plan on a much wilder ride during peak flow.

To help select target flow ranges, I like to use American Whitewater, ask friends who have run the stretch before, and search for trip reports from fellow boaters that give the flow. With all these resources, I can confidently select appropriate dates for my permit lottery application. Then the only thing left to do is hope the lottery is kind.