Provo River Spring Runoff; a Look at Historical Water Flows and Trout Habitat Provo River Spring Runoff; a Look at Historical Water Flows and Trout Habitat

Across from Little Lunker on Upper part of Middle Provo with stream at 1600 cfs in 2017.

Everyone seems to be talking about the water flow on the Middle Provo again this week since the flow just bumped up to 1800 cfs yesterday (May 19, 2020). People are saying they don’t remember this much water this early.

Well, memories of events can be wrong.

Every Spring we get questions about when the runoff starts on the Middle Provo and when the flow reduces enough to fish again.

So, I will update this post every Spring after the runoff starts, so at least I can remember correctly.

Is the Middle Provo Un-fishable?

First, I have never seen the Middle Provo so high it couldn’t be fished. Obviously, after the water has been increased by a large amount, there can be debris flows which would be difficult to fish. And if flows increase very quickly, fish will have to find places they can hold in the river without spending too much energy. The increase in water also lowers the temperature, so insect hatches are also affected.

There are sections that are not safe to wade and some of the favorite places are not easy to access (especially hard to find safe places to cross), but the fish are in the water and they are going to eat. So you just may not be able to fish your favorite holes, but you can still fish.

As example, here is a short video I took of the upper part of the Middle Provo when the flow was about 1,600 cfs in 2017. The end of the video shows our buddy Rod catching a fish. The battery died before he landed it, but you can clearly see the fish jump out of the water as it was hooked.

The Middle Provo is a tail water that comes out of Jordanelle Reservoir, so all of the initial flow is controlled at the dam. There is a minimum established flow (legal requirement) of 125 cfs to maintain fish populations and minimal water to the riparian zone, but the flow is usually maintained about 150 cfs through the winter.

As Spring arrives, the flow needs to be increased for several reasons.

Irrigation demands in Heber Valley
To maintain water levels in Deer Creek Reservoir, which in turn feeds water in the Lower Provo River
Remove excess runoff (from snow Melt) from Jordanelle Reservoir

The main factors that determine the amount of water that needs to be released in the Spring depends on how much water is being stored in the mountains as snow, how much water can be absorbed in the soil and how fast that snow melts.

Timing and Duration of Spring Runoff – Middle Provo River

Back to the question of when does the flow increase; How high can it go and when does it return to “fishable” levels?

But first, let’s define “fishable”. From many people I have talked to over the last several years, fishable water flow appears to under 700 cfs.

As another example the river can be fished successfully in high water. Last May, we had several guided trips during high water, all with beginning fly anglers, so we obviously would have prefered to have less water.

provo river brown trout with backcountrychronicles fly fishing

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One morning the water was running about 925 cfs. By the time the data was averaged, the flow was 942 cfs below the Jordanelle dam that day. Our “rookies” managed to dodge two thunderstorms and still catch 14 fish on the first day the flow increased over 900 cfs. And one of our students was 15 years old (see photo).

I think that shows the river is fishable at 942 cfs and in the video as Rod proved fish could be caught with the flow at 1,600 cfs (but I would not advise everyone to attempt wading through the side channel he had to cross).

Water Flow Data for Middle Provo River 1993 – 2020

I looked back over the historical flow data to answer the questions:

When does the flow on the Middle Provo River rise above various levels (800, 1,000, 1,200 or 1,400 cfs?
And how long does the flow stay above those levels?

The first table shows the number of days the flow was above the indicated level (Cubic Feet per Second – cfs). For example, in 1993, the river ran at least 400 cfs for 79 days, at least 600 cfs for 58 days, at least 800 cfs for 55 days, 50 days at least 1,000 cfs and ran 1,200 cfs for 45 days and ran at least 1,400 cfs for 32 days.

Next, look at Table 2 and still using 1993 as example, 58 days with at least 600 cfs occurred between May 5 and July 7.

The flow was at least 800 cfs between May 5 an July 5 and at least 1,000 cfs between May 13 and July 3.

Flow in the Middle Provo was also at least 1,200 cfs between May 14 an June 30 and at least 1,400 cfs between May 14 and June 29.

The latest in the season the River ran over 1,000 cfs was July 13, back in 1995. In the last 10 years (2010 – 2019), the latest the flow was above 1,000 cfs was July 12 in both 2010 and 2011.

The latest in the season the River ran over 600 cfs was Sept. 14 in 2016.

Table 1 Spring Runoff – Middle Provo River – NumberThe latest in the season the Middle Provo River ran over 1,000 cfs was July 14, back in 2010. of Days Flows above 400, 600, 800 and 1,000 cfs.

* 2020 data not complete

Table 2 Spring Runoff – Middle Provo River – First & Last Day Flow above 600, 800, 1,000, 1,200 and 1,400 cfs.

* 2020 data not complete

Notice that gray areas in the both tables represent that flows did not reach the required levels.

In 2007, flows never reached 800 cfs, and did not go above 600 cfs until Aug. 18.

In 2014, flows never got above 400 cfs at all.

It was only two years ago (2017), that we had the highest flows since 2011. In fact, except for 2 days in 2016, we haven’t seen flows over 692 cfs since 2011.

There were many years (1993 – 2006) when maximum flows were never less than 1,100 cfs, so we have seen the drought reflected in the flows on the Middle Provo up until 2017.

One thing that should stand out for those that look closely at the tables, is there appears to be no regular pattern or formula that is being followed, but we also don’t know the timing or the inflows of water from the Upper Provo River into Jordanelle.

We also don’t know how the irrigation demands change from one season to the next (though it seems that everyone is running sprinklers all the time, but each year there are more lawns to water) and we don’t know how much other factors like the toxic algae (cyanobacteria) in Utah Lake dictates how much water is run during the Summer.

I am sure many factors determine the timing and magnitude of water released from Jordanelle Reservoir into the Middle Provo. But we never see any forecast, schedule, justification and we are never asked for input. I would also like to know if Jordanelle dam has the ability to mix in some warmer water into the flow or are they limited to taking cold water off the bottom of the reservoir. These factors have huge implications for the fish, the hatches and stream quality.

What does High Spring Flow mean for Fishing?

When the spring runoff comes, for one thing, it changes the amount of the best habitat for trout.

There was a stream flow study done for the Middle Provo River in 2004 (click here to download pdf). The study (in part) modeled different flow regimes to predict how much habitat would be available for fish.

I borrowed and modified two figures below from that report. The first Figure; Provo River Habitat Niches shows 8 different aquatic habitats based upon water depth and stream flow.

Provo River Habitat Niches

As examples of those habitats, #1 Backwater edge (bottom left of figure) can be any depth up to about 150 cm (59 inches), but must have water flow less than 0.1 meters per second (m/s).

#4 the Fast/Shallow habitat is less than 40 cm with water flow greater than 1.0 m/s.

#5 Moderate/mid-depth is up to 120 cm deep with water flow less than 1.0 m/s.

The adult Brown Trout and Whitefish (and rainbow trout) spend most of their time in niches #5 and Whitefish also use Niche #7.

Refer to the Figure below Provo River Habitat Niches – to see all 8 Habitat Niches

Trout obviously spawn in shallow water and small fry live in shallow water, but adult fish spend most of their time in deep water with flow less than 1.0 m/s. In fact the report does not give any value to fast water to adult fish habitat.

Since we all have caught fish in deeper and faster water, this is a generalization and not an absolute, set in concrete fact. Basically, fish can use faster segments of water, but are usually at the bottom where the speed is not so fast. But to simplify the models, this is what they came up with.

Figure – Provo River Habitat Niches

So given these definition of fish habitat, how do the amounts of the habitats change as the water flow increases?

The amount of habitat is basically defined in the study as the Weighted Usable Area (WUA), which is defined as the total area per unit length of river that would be expected to provide usable habitat for a species. In this case, adult brown trout (which they assume only uses Niche #5). To include rainbows (and cutthroats; very few if any remain now), they included a little more of the shallow water habitat.

Suitable Trout Habitat

In other words, how much of suitable habitat is available for all trout with different water flows and that amount is measured in the number of square feet per linear foot of the river.

The next figure (also modified from the 2004 flow report), shows how the WUA (habitat) should change with increased flow.

It should be noted that this part of the study was done from measurements taken on the upper part of the Middle Provo, just downstream of the US-40 bridge.

The report states “Adult trout results show that the large amount (> 20,000 ft2 / 1,000ft) of habitat is available at flows greater between 25-900 cfs”… and this can bee seen in the figure below (note – by law, the Middle Provo should never be below 125 cfs – marked on the figure).

Figure – Usable Provo River Trout Habitat vs Water Flow

So as seen in the Weighted Usable Area figure above, at minimal flows (125 cfs) there is about 40,000 square feet of adult trout habitat for every 1,000 feet of river. That translates to 0.92 acres per every 1,000 feet of river.

Can we extrapolate this for the entire Middle Provo? Take this “with a grain of salt”, because the data and the model are all based on one area, but if the Middle Provo has 12 miles of river, which would be about 58 acres of prime trout habitat in the entire Middle Provo River at 125 cfs.

58 Acres of Suitable Trout Habitat?

Let’s think about that a minute. That doesn’t sound like very much trout habitat for the entire Middle Provo River.

If the river is 12 miles long and averaged 40 feet wide, that would also total 58 acres. The river would have to average almost 69 feet wide to total 100 acres.

So it may seem like there should be a lot more habitat within the 12 miles of river, but in reality there is simply not that many acres of river surface area (or river bottom) in the entire river. To me, that makes it even more amazing that our little river can support the high fish populations that it does (with no fish being stocked in the Middle Provo river since 2003 – rainbows are stocked in Deer Creek Res., and they do run up into the river ).

It will be interesting to see the results of this year’s fish population survey and to see how much fishing pressure the river receives now.

So a high proportion of the entire river is good habitat for adult trout.

Note – Not that I want to ever see this much fishing pressure, but… All we really need at any given time is about 40 foot upstream and 40 feet downstream for each person to fish. If we fish a seam that is 4 feet wide, that is only 320 square feet. If we more than triple that amount to 1,000 square feet per angler, at 375 cfs, that 45,000 square feet of trout habitat/1,000 ft of river could support 45 anglers.

According to the models, as flow increase from 125 cfs to about 200 cfs, so does the amount of trout habitat (increases to 45,000 sq ft/1,000 feet – or 1.03 acres per 1,000 feet or about 65.5 acres for the entire Middle Provo.

As the flow increases to about 375 cfs, the total amount of trout habitat returns to about 40,000 sq ft/1,000 ft; the same as 125 cfs.

At this point, increased flow causes a decrease in the total amount of trout habitat which decreases to about 28,000 sq ft/1,000 ft at 600 cfs (40.7 total acres) and to 22,000 sq ft/1,000 ft at 800 cfs (32 total acres) and then to 19,000 sq ft/1,000 ft at 1,000 cfs (27.6 total acres).

From that point, there the amount of trout habitat does not decrease very much in response to increased flows even up to 2,000 cfs.

Trout Habitat Decreases when Flow Increases above

So yes, once flows are above 600 cfs, the amount of trout habitat decreases. That means fewer places to fish and since more people are out trying to fish this time of year, there is more crowding.

There are lots of folks scrambling around looking for other places to fish, but the many of the mountain areas are not accessible yet and the Strawberry River will probably not recover for several years.