Wisconsin Watersports Coalition

Sediment Resuspension

We cannot make Wisconsin the most RESTRICTIVE state in the nation.

A comprehensive review of studies leads to enacting a 200' setback from shore rule.

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Summary

Actual experimental and historical data conclusively proves that wake boats in 10-15 feet of water do not have a long term impact.

An extensive study performed by Daeger et al. was published in the Indiana National Academy of Science measuring lakebed disturbance in 2022 (Daeger et al. 2022). This is a comprehensive study measuring lakebed disturbance. It utilized five boats (Inboard, I/O Runabout, PWC, Pontoon, Wake Boat under ballast), four tests with several boat runs at multiple water depths in 4 areas of the lake with varying compositions. They measure five indicators of lake bed disturbance, including suspended solids, phosphorous ammonia, chloride, nitrite, sulfate, and silica. The wake boat was operated in surf mode, approximately ten mph, while the rest of the watercraft was operated at 2000rpm and "on plane." The study concluded that all boat types could disturb lake beds in 3-5 feet of water, but once all the boats, including the wake boat, operated at depths of 10-15 feet, there were no differences in any of the test results before and after the boats passed. This study is one of two studies that actually tested for an increase in suspended solids. Total suspended solids are a key measure of water clarity. It indicates the amount of small particles, like silt, sediment, and algae, suspended in the water. After the wake boat passed at 10-15 feet, the data concluded there wasn't an increase in suspended solids, immediately after the boat passes, when suspended solids would be the highest if present.

The results of Draeger et al. are consistent with those of Raymond and Galvez-Cloutier (Raymond & Galvez-Cloutier 2015). This study measured water velocity using an acoustical probe at various depths following the passage of a wake boat. At 15 feet, water velocities had decayed to 0.1 m/s. The authors speculated that would be sufficient to resuspend small particles, but actual testing using multiparametric probes, turbidity, conductivity, and dissolved oxygen were measured and didn't result in any significant variation in these parameters. In addition, the actual diver did not observe any difference in sediment before and after the boat passage.

The anti-wake boat groups cite studies that rely on computational modeling of water velocity, not actual sediment resuspension. These studies attempt to predict the potential impact of propeller wash on lake beds, with conflicting conclusions. The study by Ray is often used to support claims of impacts down to 30 feet. This study uses models for turbulent jets, and extrapolates them to create velocity decay profiles. This computational work was never validated experimentally and is inconsistent with actual measured velocity profiles. There is no experimental evidence that suggests there is sediment impact beyond 10-15 feet.

A 2022 study by Terra Vigilis (Phase 2) is frequently cited in condition reports accompanying ordinance proposals, particularly to support the claim that "wake boats increase phosphorus levels." The study aimed to determine whether boating activity, including wake boats in surf mode, contributes to elevated phosphorus levels. One commonly referenced data point from the Phase 1 part of the study indicated a 25% increase in phosphorus levels 30 minutes after a wake boat in surf mode passed nearby. However, the study did not test any other watercraft, leaving it unclear whether this result is specific to wake boats.

However, during the Phase 2 testing in 2021, phosphorus samples were collected on both a single day and over the summer at a specific site known for plume deposits. On the single day of testing, a Tuesday, seven sites were sampled at four-hour intervals starting at 8 a.m. Phosphorus levels varied between 23-200% across all the sites and up to 45% from the same sites, all without isolating for wake boat activity. Furthermore, over the summer, phosphorus levels at the same site fluctuated by 46%. In their summary, the researchers noted that the sediment redistribution no effects from wake boats activity were "notable", but then go on to acknowledge that "this sediment deposition could not be solely attributed to wake boats." Ultimately, the observed phosphorus increases fall within the normal range of variability in their data, rendering the connection to wakeboat activity statistically insignificant.

Data from Wisconsin lakes do not support claims that wake boats increase turbidity and algae blooms. The WI water quality data is excellent and shows no deterioration in lake clarity since wake boats were introduced in the last 15+ years. For example, Anvil Lake in Vilas County is a 377-acre lake, and several wake boats have been on the lake for years. Anvil Lake takes data yearly to monitor the health of the lake. As you can see in Figure 1 below, if wake boats had a significant impact, the data would reflect that by showing a shift since wake boats have arrived. Any lake that is tested in conjunction with the DNR will have their lake's information on WEx WDNR https://dnr-wisconsin.shinyapps.io/WaterExplorer

The preponderance of data doesn't support the argument that these boats are "tearing up plants" even at depths of 15 ft. In fact, the testing supports the opposite. At a depth of 10-15 feet, the water velocities do not reach the speed to drive sediment resuspension. Finally, these arguments are also made, ignoring the presence of other boats on the water. For every wake boat, there are 25 other watercraft on the lake. If we are to take Raymond, Youssef, Beachler, Anthony and Terra Vigilis work at face value, any boat with a greater than 50hp engine operating in less than 10 feet of water is an equal concern for sediment resuspension.

Wisconsin Lake Data (DNR)

The data from Wisconsin lakes do not support claims that wake boats increase turbidity and algae blooms. The WI water quality data is excellent and shows no deterioration in lake clarity since wake boats were introduced in the last 15+ years. For example, Anvil Lake in Vilas County is a 377 acre lake and has had several wake boats on the lake for years. Anvil Lake takes data yearly to monitor the health of the lake. As you can see in Figure 1 below, if wake boats had a significant impact, the data would reflect a deterioration in lake clarity since wake boats have arrived, around 2010. This however, is not the case, as the data shows stable water clarity across the many years since the arrival of wake boats. This stable trend is seen consistently from lake data that is collected across the majority of Wisconsin lakes.

Any lake that is tested and has been working with the DNR will have their lake's information on: WEX WDNR https://dnr-wisconsin.shinyapps.io/WaterExplorer

Figure 1:

Indiana Academy of Science Study (Daeger)

The Indiana National Academy of Science published a definitive study measuring lakebed disturbance. This experimental work examined several sediment resuspension test parameters (suspended solids, nitrogen, phosphorus, etc.). It also used several different boat types, including a ballasted wake boat, and utilized four separate areas of the lake to see if lakebed composition would affect the data. The wake boat was operated in surf mode, approximately 10mph, while the rest of the watercraft were operated at 2000 rpm and "on plane". The study concluded that all boat types can disturb lake beds in 3-5 feet of water, but once all the boats, including the wake boat operated at depths of 10-15 feet, there were no differences in any of the test results before and after the boats passed.

The key position by groups advocating for the bans on wake surfing is that these boats will increase phosphorus levels due to sediment resuspension. Not only did the study not reflect an increase in phosphorus levels, more importantly, it concluded that suspended solids didn't increase at the 10-15 foot depth directly after the boat passed, let alone long term. This directly refutes the anecdotal and speculative claims that the lake bottom is experiencing extensive sediment resuspension from wake surfing alone.

To date, this study has provided a more rigorous test methodology and procedures than other tests that utilize speculation, providing actual testing results from multiple sites, depths, and boat types.

Figure 1 below shows the results of the testing.

Figure 1:

Laval University (Raymond)

This study utilized acoustical probes to measure underwater intensity and velocity. The testing protocol included multiple boats, including a wake boat tested with both wakeboarding and wake surfing activities. When a boat passed over the acoustical probe, the probe provided a graphical representation of the velocity down to 0.1 m/sec.

The results indicated a velocity of 0.1 m/sec was seen as deep as 13-15 ft. for the wake surfing activity, although the data is very noisy, making precise depth determinations challenging. As a comparison, the pontoon tested(100hp) appears to have seen this velocity at a depth of 7-9 ft. Based on previous work, it is speculated that 0.1 m/sec has the potential to move sediment with a size of 0.05mm diameter. Therefore, they state, "...it's potentially possible for these vessels to resuspend sediments of 0.05mm...." For visual confirmation, the study placed a diver at approximately 15 ft. to identify sediment resuspension. That diver "did not notice any material suspended as a result of boat passage."

The study references several previous studies and work completed on sediment resuspension. Work often cited in several studies is that of Youssef and Beachler, starting in the late 70's and continuing into the 2000's.

Raymond states, "Beachler (2002) theoretically indicates, and observations confirm, that a rate of movement of a 0.3mm sand particle is about 25 cm/s while a clay particle of 0.05mm requires a water velocity of 12 cm/s." Yet the diver didn't see any sediment resuspension.

Raymond also cites a study by Beachler, which includes a graph of the “Maximum Bed Velocity” versus “Boat Speed,” measuring water velocity at depths of 4 to 6 feet using a 150hp motor. The study indicates that the maximum underwater velocity occurred at approximately eight mph but decreases sharply after nine mph, dropping by nearly half as boat speeds approach 11 mph (common for wake surfing). Field data from the study show that at a depth of four feet, water velocity decreased from roughly 60 cm/s at eight mph to 25 cm/s at eleven mph. At a depth of six feet, velocities were about 35 cm/s at eight mph and 20 cm/s at eleven mph. These findings illustrate that water velocity decreases significantly with just a minor 2 mph speed change and a 2-foot increase in depth.

Although boat engine sizes have increased since the study, the data from Beachler may help explain the lack of observations regarding sediment resuspension at depths greater than 10-15 feet. Lastly, Raymond notes that Anthony and Downing also found a weak correlation between boat traffic and sediment suspension.

Terra Vigilis (Phase 1 and Phase 2)

The Terra Vigilis Study is often cited in the condition reports linked to the ordinances due to it's use of actual test data.

This study was conducted to look at wave heights, plumes and to test if there was an increase in phosphorus due to boating activity, including wake boats in surf mode passing nearby. A data point from the Phase 1 testing that is regularly presented is that a 25% increase in phosphorus was observed thirty minutes after a wake boat in surf mode passed by. Unfortunately, they didn't test any other watercraft to understand if these results were attributed solely to wake boats or surfing.

Additionally, during their phase 2 testing in 2022 they collected phosphorus samples for both a single day, and over the summer looking at a specific site on the lake known for plume deposits. For the single day, they tested seven sites on the lake for phosphorus, taking four samples at approximately four hour intervals starting at 8am. Within one day, a Tuesday, without testing for boat activity the results showed a 23-200% change in phosphorus across those seven sites. Furthermore, the samples over the summer at Site 3 saw a 46% variation in phosphorus.

In their summary, they claim that re-desposition effects are "notable" from wake boat activity but soon after state that "this sediment deposition could not be solely attributed to only wake board boats...". In conclusion, the increase in phosphorus they attribute to a wake is within the normal variation of their data and is statistically insignificant.

Finally, the study stated, "Demonstration of the actual impact to the bottom was not within the design of the Phase 2 study.” Overall, this study provides a weak to non-existent correlation between phosphorus levels, suspended solids and wake surfing activities.

Terra Vigilis Lake Waramaug Study

Issues with the Study:

There was no editorial or third-party validation of these results. It was self-published without review.
The boat was operated at a speed that maximizes prop wash (9 mph, with a Froude number of 0.51), which is not representative of typical wake surfing conditions ( 11 mph) and did not compare to more representative watercraft such as a deckboat or fishing boat.
The study relies on non-quantitative video imagery without calibration.
Claims are inconsistent with previous quantitative research.
The assertion of increased phosphorus levels lacks appropriate controls for total variability.

Boat Operation and Wake Surfing Conditions

The boat was operated at 9 mph. This does not reflect typical wake surfing conditions, making the study's applicability questionable. Furthermore, the study only compared results to a ski boat operated at a much higher speed. A more appropriate comparison would be a comparable boat operating at tubing speeds (10-15 mph)

Use of Inferior Measurement Techniques

The study utilizes video cameras to detect water movement, an approach significantly less reliable than methods employed in previous research. For example, Raymond and Galvez-Cloutier measured actual water velocities, providing quantitative data. The authors offer no explanation or visual comparison of natural water variation or the velocity required to move the streamers used in their analysis. Prior research has shown that:

Water velocity >12 cm/sec is needed to disrupt fine silt.
Water velocity >25 cm/sec is required to disturb sand.

Free-hanging streamers react to any water movement, but without precise velocity measurements or data on natural current variation, the study fails to establish a meaningful link between streamer movement and sediment resuspension. Furthermore, the report claims an effect extending 26 feet, based on a single image of sediment on a brick, without specifying the duration required for sediment deposition. There was no control to confirm that sediment accumulation resulted solely from the wakeboat pass or that other boats such as a deckboat tubing would not cause a similar result. The absence of time-lapse imagery or baseline conditions makes it impossible to assess the actual impact.

Superior methodologies measure water quality directly, such as suspended solids(turbidity), dissolved oxygen, etc., yielding quantitative data that contradicts the findings presented in this study.

Contradictions with Established Research

The most comprehensive study on lakebed disturbance, conducted by Daeger et al. (2022), measured suspended solids, phosphorus, SiO2, and nitrates. Their findings indicate that a ballast wake boat does not have an impact beyond 10-15 feet, even in areas with fine sediment. In shallower waters (3-5 feet), all types of boats can resuspend sediment.

Similarly, Raymond and Galvez (2015) used acoustic probes capable of detecting water speeds down to 10 cm/s at 15 feet. Even when they detected water velocities of 10 cm/s their diver observed no material suspension resulting from boat passage. Additionally, their use of multiparametric probes to measure turbidity, conductivity, and dissolved oxygen showed no significant variation at 15 feet. The authors concluded that wakeboat impact did not reach this depth, and that the lakebed consisted of larger sand particles rather than silt—contrary to the study’s visual evidence. Despite the greater reliability of these quantitative studies, the authors of the current study fail to reference or explain their inconsistencies with established findings.

Unsubstantiated Claims in Ray (2020)

The study by Ray (2020) claims that boats impact lakebeds beyond 30 feet, yet this assertion was not peer-reviewed and lacks supporting measurements. The author does not hold credentials in fluid mechanics, and the study relies on modeling techniques that are inconsistent with more rigorous finite element modeling efforts. While it calculates theoretical water velocity and suggests a corresponding impact, experimental research contradicts these claims. The study provides no empirical evidence, rendering its conclusions unreliable.

Issues with Phosphorus Measurements

The authors claim that phosphorus levels doubled after a wakeboat pass at 20 feet, yet they provide no quantitative data or discussion of normal variability, making it impossible to determine statistical significance. Their only reference point is that phosphorus did not increase following a ski boat pass, yet no comparative data is provided. Furthermore, they caution that this finding is "preliminary in nature, was not the primary focus of the project, and warrants additional study." If the data is preliminary and lacks a baseline, its inclusion in the report is questionable.

To support their phosphorus claims, the authors reference their prior study, which examined phosphorus when a wake boat passed and levels throughout the summer. After the wake boat passed (no additional watercraft were tested), results indicated phosphorus increase of up to 25%. However, when testing Site 3 throughout the summer, the study found variations of up to 48% in phosphorus levels. Additionally, they conducted a one-day phosphorus test in August, selecting a Tuesday with reduced watercraft activity, the study collected samples from seven sites at four-hour intervals. This resulted in:

23-47% variation in phosphorus levels at individual sites.
Up to 200% variation across all sites in a single day.

Given this inherent variability, drawing conclusions from a single wakeboat pass is highly questionable. Without proper controls and a comprehensive analysis of natural phosphorus fluctuations, the study's claims remain unsubstantiated

Big Payette Lake (Ray)

This study utilized calculations and models but lacked any actual measurements for sediment resuspension. Furthermore, the modeling is not consistent with more rigorous finite element modeling efforts.

The study calculates water velocity and then speculates impact. Ray ultimately concluded that wake boats in surf mode could affect the sediment up to a depth of 30 feet. We already know through other independent studies (listed above) that conducted more specific testing and data collection that this speculation doesn't reflect the actual test results obtained.

References:

Daeger, Bosch, Johnson,et, "Impacts on Nutrient and Sediment Resuspension by various Watercraft Across Multiple Substrates, Depths, and Operating Speeds in Indiana’s Natural Lake. (2022. Proceedings of the Indiana Academy of Science 130(2):112–122)) Daeger Study

Tyre, et, (2021-2022) "A Phased Study of the Water Quality and Wave Propagation Dynamics Currently Impacting a Small Southeast Wisconsin Freshwater Lake: Waukesha"; (Phase 1 - 2021; Phase 2 - 2022) Terra Vigilis Group

Raymond, S., and Galvez-Cloutier, R., (2015) Impact of Lake Navigation - SedimentSuspension Study: Lake Masson and Sand Lake Cases, Laval University. 30p. (Published inFrench, English translation)

Knutson PL, Allen HH, Webb JW. (1990). Guidelines for vegetative erosion control on wave-impacted coastal dredged material sites. Technical Report D 90-13. Vicksburg (MS): Army Engineer Waterway Experiment Station, Environmental Laboratory, 33p

Ray, (2020) Analyzing Threats to Water Quality from Motorized Recreation on Payette Lake, Idaho; Western Colorado University