Submersible Mixers - 1992-93

The Students: J. J. Conrad, Jon Stiles, and Kenna Thomas

The Teacher: Clinton A. Kennedy

Awards: 1993 Seiko Youth Challenge West Region Semi-Finalist and Finalist and West Regional Champion, awarded $5,000 scholarships

The Implementation of Resource Management Systems and Submersible Propellors to Efficiently Attain the Destratification of Cascade Reservoir

Summary Page

The ECO-trio is a tri-person effort dedicated to improving the water quality of Cascade Reservoir in Cascade, Idaho. Cascade Reservoir is a 26,000 acre impoundment of the North Fork of the Payette River, located in Central Idaho. For years it has been ranked one of the leading fishing lakes in Idaho, and is vital to the tourist-based economy of our community. But lately, this has been threatened by anoxic conditions occuring during stratification as a direct result of ultra eutrophication.

The project idea we have conceived involves the implementation of ITT Flygt submersible propeilors as a short-term solution, providing the necessary time for the long-term projects to become effective, based on the Resource Management Systems. The mixers appealed to us as effective, simple, and relatively inexpensive compared to other applicable ideas.

The project we propose is original in the fact that it has never been administered in Idaho, and is a relatively new approach toward water management.

Our research delves into the depths of the land. We succeeded in elevating our project to an international level when we contacted Sweden about their Flygt submersibles. Much of our research involved field work. We performed several water quality tests on the reservoir, as well as testing tributaries and examining wetlands. Further research involved a variety of companies throughout the United States, including several experts on limnology, destratification, water quality enhancement, and various influencing organizations locally and throughout the United States. The advanced biology class' recognition was amplified when we appeared on public television in December.

While the numerous problems in the lake seem entirely impossible to solve all at once, well...they are. That is why our group is presenting a short-term solution plan to allow us time to administer the long-term plans which should solve the problems with the lake permanently. Only through careful management and dedicated time and money, is the
preservation of Cascade Reservoir even possible. Our group is indebted to everyone who helped in any way to aid our project. We hope that our proposal will be accepted, and even if it isn't, we will still try to do everything possible to aid in the recovery of our lake.


In the beginning, there was the Advanced Biology class, a coordinated group of students who were prepared to learn. Our first trip to Cascade Reservoir was located near the dam. It was a sunny day, clear and hot. The faint odor of decaying fish wafted in on a swift breeze. Several noses crinkled in distaste. The water lapped sullenly at the beach, leaving faint traces of green on the sand. The problems with the lake were immediately evident, but the solution was not so prominent.

During our first trip to the lake, we took notes on our surroundings, and performed several water quality tests. We recorded measurements of pH, phosphate, nitrate, carbon dioxide, dissolved oxygen, BOD (Biological Oxygen Demand), water depth,and water temperature.

On our second trip to the lake, we performed the same tests at the same location at a deeper depth. Our results were not pleasing. For the time of year, which was fall, our phosphate levels were overabundant.

Algae is our greatest enemy in the lake. There are too many of them, and they must die. Phosphate is our limiting reagent, so the logical solution to the algae problem is to lower the phosphate level. However, this is easier said than done.

We executed our tests at several other sites around the lake. We also took a field trip to Boulder Creek with the DEQ (Department of Environmental Quality), and visited several riparian zones. We learned exactly how important our wetlands are to the environment. Our class accompanied the DEQ as they demonstrated water tests on Boulder Creek, and performed a fish-shocking expedition. We also attended a CRA (Cascade Reservoir Association) meeting in Donnelly, at which was discussed possible solutions of the reservoir. Among other great and numerous achievements, our biology class appeared on Incredible Idaho, a prime time environmental television show about Idaho. The television crew filmed us performing our water tests at the Gold Fork site, which is located on the northern end of the lake.

A simple but effective process to check water quality is to take a species ratio. We practiced this method on Boulder Creek to find if the pollution in the lake might be caused by a tributary. With the DEQ, we studied the ratio of macroinvertebrates to calculate the water quality. For example, and abundance of mayflies would signify clean water, while a large blackfly population would mean pollution. On Boulder Creek, the macroinvertebrates signified fair water quality.

Dennis Taggart and Rick Orton presented our class with a slide show and talked with us about the planned Val-Bois ski resort and its environmental impact on the lake and the surrounding wetlands.

The fish in the lake have only a narrow area to live in, which is limited by thermostratification. Only 14% of the lake will support trout during summer stratification. In the winter, snow covering the ice on the lake blocks any light penetration, so the anoxic zone widens.

There are three main ways in which oxygen gets dissolved in water. These are atomic decomposition, photosynthesis, and aeration. Our project focuses on the latter, aeration, which is mostly achieved by waves and the churning of water, combined with the temperature and the saturation rate.

Overabundance of nutrients is a major problem in the lake. In the last ten years, the nutrient level has increased approximately 38%. Nytella, which is the overbearing dynoflagellate in our reservoir, is a rooted plans, but is easily torn loose and can survive while floating. Nytella are very dependent on high nutrient levels to keep a distinct advantage over other plants, which they do very efficiently.

Dynoflagellates are a problem in eutrophic lakes because they form large mats just under the surface of the water. These mats clog boat motors and prevent any kind of recreation in the lake. They are also the source of the bad odors, for when the wind blows, these plants are washed ashore, where they decompose. Dynoflagellates are a sign of bad water quality, and can cause red tide, which is a lethal toxin.

The fish suffer a direct mortality in the summer when concentrated algae blooms float in towards the shore when the wind blows. This algae takes over, and smothers the baby perch which usually flourish in the littoral zone.

Another problem in the reservoir is the farmers. The lake was originally intended as a draw-down reservoir, to be used by the landowners for irrigation. This year's drought meant a drastic decrease in the water supply of the lake, as both nature and man took their shares. Attached benthic algae should be seen in large amounts in lakes, but is almost absent in Cascade, for there is never enough time for them to form before water is removed.

The fish are dying, the recreation industry is in danger. Everyone wants their own way, while algae are planning a takeover. The future of Cascade is very dependent on the lake, and if we were to lose it, everyone would suffer disadvantages. With the preservation of the lake being such a high priority, we can't afford not to take care of it. All in all, this looks like a job for . . .the ECO-trio.

ITT Submersible Propellors

In response to the anoxic, stratified condition of the lake, we propose to implement submersible propellors as a short-term solution to keep the complications under control until the more permanent approach of Resource Management Systems takes effect. Throughout our numerous conservations with ITT Flygt Corporation, we discussed the possibilities of establishing a pilot project in which Flygt Corporation would contribute to the restoration of Cascade Lake by donating equipment. Although we have been limited by time, local circumstances, (weather, other proposals, etc...) and money, we plan to continue our pursuit. Justifications for our choice include the feasibility, efficiency, and
durability of the product. Taking into consideration the forementioned factors, the submersible mixers proved to be the most promising of ail locally proposed solutions.

As we researched various methods of water quality improvement, we continually encountered logistical problems such as financial sarifice and adverse effects of installment. ITT Flygt submersible propellors proved to be a more feasible solution. We did face logistical problems concerning the propellors; due to the size of the lake, it would take an unreasonable number of mixers to circulate the entire water column. However, upon further, investigation we discovered that only a select few areas actually suffer from thermal stratification and they, in turn, affect the remaining portion (the majority) of the lake. Consequently, we would need only to locate the main areas where stratification occurs and install mixers accordingly. Among other solutions, one organization concerned suggested aerators and aluminum sulfate treatment. Aluminum sulfate treatment is a temporary measure, probably only lasting for 1-2 years in our reservoir due to watershed nutrient input, with a preliminary capitol cost of $6.5 million. Quite obviously, such a proposal is out of the question. While aerators would increase the oxygen content of the water, they are considerably more expensive and would require far more extensive facilities to maintain. An aerator would require a serarate generator located near the lake, pipelines running from the generator to the aerator, and, due to the weather conditions and incredible noise, a large, insulative encasement would need to be erected around the generator. The propellors, on the other hand, would be installed directly in the lake itself, and would provide efficient results, as will be explained in more depth momentarily. According to the Cascade Reservoir Watershed Project Water Quality Management Plan, the capitol cost of an aeration system for Cascade Reservoir could range anywhere from $100,000 to $1.2 million. The involved organizations have decided that, due to the desire to have the maximum Oxygen delivery capacity, the $1.2 million calculation should be used for comparison with other restoration techniques. We could activate 5 submersibles with a capitol expenditure of less than $500,000. For the price of installing and operating one aerator, we could implement and maintain several submersible mixers, thereby increasing the effectiveness of the destratification process.

As mentioned earlier, the efficiency of ITT Flygt submersible mixers proves them to be a feasible method of water quality improvement. The propellors have a maximum immersion depth of 130 feet, whereas the maximum depth of Cascade Lake is approximately 68
feet. Maximum liquid density able to be transported is 9.2 pounds per gallon, while the greatest density of our lake is approximately 8 pounds per gallon, occurring during the winter. Incidentally, operation of the propellors would continue during the winter, melting the ice in the area, exposing more water to natural aeration, which, in turn, further increases efficiency. Providing high flow capacity in relation to power consumption, mixers use less electricity than aerators. A 7 horsepower propellor would require approximately 5 kilowatts per hour and would transport 5-10 m3, while a 1,500 horsepower aerator would require significantly more and doesn't actually circulate the water, consequently limiting oxygen circulation. According to our calculations, 5 propellor apparatus stations would be sufficient not only to control present conditions, but to improve water quality as well. After having observed the original 5, a decision will be reached concerning the necessity of greater or fewer quantities.

The final determining factor which we will discuss is the durability of ITT Flygt submersible propellors. As indicated in the Flygt Technical Specification informational brochure, there are many features which contribute to the durability of the product. The consideration of endurance which entered into the product design is obvious when one researches the product. As stated in the Product Description, the junction box is completely sealed off from the surrounding liquid. The motor is designed to supply its rated output at +/- 5% variation of the rated voltage, and without overheating the motor, a +/- 10% variation can occur provided that the motor does not run continuously at full capacity. The gear unit is calculated in accordance with ISO and AGMA for more than 100,000 hours of continuous operation. The motor shaft bearing consists of a single-row deepgroove ball bearing as a supportive bearing and a double-row spherical roller bearing as the main bearing. The mixer's bearings are also calculated for more than 100,000 hours of operation. An oil casing lubricates and cools the seals, bearings and gears, and acts as an additional barrier against penetrating liquid. Pressure build-up is prevented by means of a built-in air volume. The double-bladed propellor is backward curved to prevent ciogging. Many insightful considerations are evident in the design of the ITT Flygt submersible mixers.

It now seems appropriate to explain exactly how ITT submersible mixers improve water quality. Normally, lakes maintain their ecological states naturally. However, occasionally the epilimnion (surface) and hypolimnion (bottom) are divided by a distinct drop in temperature which occurs suddenly. This area of change is known as the thermocline and prevents the exchange of water between epilimnion and hypolimnion, thereby leading to anoxic conditions in the hypolimnion as bacteria use the oxygen supply to decompose detritus. Once anoxic conditions are reached, the bacteria begin to use the oxygen molecules present in phosphates, releasing free phosphorus ions for the overly-abundant algae to feed on. This barrier is removed only twice per year (spring and fall) when the temperatures become equalized, allowing the water of different layers to circulate. The mesolimnion (middle) area, where most fish species of Cascade thrive, is also decreased by thermostratification (the layering of lakes due to temperature fluctuations). Submersible propellors involve transporting large quantities of water across the thermocline. The exhausted water in the hypolimnion circulates into the epilimnion, simultaneously renewing the oxygen supply to the hypolimnion and extending the mesolimnion. The effect is promoted oxygen take up, stimulated biological breakdown of dead vegetation, and new life achieved in the water.

Resource Management Systems

Serving as a follow-up to the ITT Flygt submersible mixers, our implementation of Resource Management Systems (RMS) will have an incredible positive impact on existing water quality problems. Reduction of sediment and nutrient loads delivered to the streams will improve water quality and protect beneficial uses. With the use of RMSs, involving the implementation of Best Management Practices (PMP), nutrients and sediments will be reduced, thereby improving water quality. Our goal, along with the installation of the ITT Flygt submersible mixers, is to achieve complete installation of RMSs whenever possible. This proposal has already been agreed upon as a future course of action by several locally involved organizations. The following is a listing of various BMPs that are possibilities for courses of action to follow the expiration of the mixers:

-Pasture Management

This BMP is used to prevent overgrazing, maintain the best plant forage species for the herd, protect the soil, and reduce erosion and nutrient water quality impacts. Implementation involves proper location of water for livestock to minimize travel and trampling; selective application of fertilizer to maintain healthy pasture forage; and pasture
rotation or deferred grazing to prevent overgrazing of a given unit.

-Pasture Planting

This involves the planting of grasses and legumes on damaged pastures or land that is being converted to pasture from other use. This may involve rough tilling or deep furrow drilling, depending on soil conditions, to enhance planting success. The overall purpose is to reduce wind and water erosion and improve receiving water quality, while enhancing pasture conditions for the herd.

-Planned Grazing System

This involves the application of two or more grazing units which are rotated seasonally to meet livestock feeding needs while preventing pasture deterioration, soil erosion, and/or nutrient export from the unit. Additional fencing and stock watering facilities may be needed in conjunction with planned grazing systems.

-Nutrient Management

This BMP us used to provide supplemental nutrient supplies to pastures and crop lands, without overfertilizing, and in a manner that minimizes nutrient losses to ground and surface waters. Fertilizer application rates should be based upon soil conditions and plant needs. Timing should be planned to avoid periods of high runoff or soil leaching. Fertilizer can be applied via sprinkler systems but not by flood or surface irrigation.

-Irrigation Water Management

The purpose of this technique is to manage irrigation practices in a way, so as to meet all the water needs of crop or pasture land, while minimizing erosion and nutrient losses. In Cascade Reservoir, irrigated pasture land is a dominant agricultural use for which improved irrigation management could result in reduced phosphorus loading. There is some indication that irrigation rates could be lessened to reduce total irrigation return flow and nutrient loading, and improve irrigated pasture conditions. Presently, excessive irrigation is producing undesirable wetland plant species. Reducing the rate of irrigation would cause these to be replaced by more desirable plants and result in reduced nutrient
loading from these areas.


This is intended to prevent livestock access to stream and river banks or other areas where erosion problems can be worsened by tramping and/or where livestock manure can contribute significantly to nutrient loading. In addition to traditional barbed wire fencing, barbless or electric fencing can be considered; in some cases, vegetation can be planted to provide effective livestock barriers. When planted along stream corridors, vegetation can also provide enhanced streambank stabilization and erosion control. Where direct stream access is cut off, alternative stock water systems may be needed.

-Chiseling and Subsoiling

This technique is used to break up and loosen hard or compacted soil layers with minimal surface soil disturbance. Chiseling (up to 16 inches) and subsoiling (deeper than 16 inches) help water infiltration, reduces runoff volumes and erosion and nutrient export, while enhancing root penetration and promoting plant vigor. This is typically applied to
relatively deep soils (over 20 inches) of medium and fine textures. It is most effective in situations where compact surface soils preclude water percolation to deeper, more permeable layers.

-Proper Grazing Use

This technique tries to prevent overgrazing and soil erosion and nutrient losses. Applied to range lands, it is somewhat different than grazing controls for pasture lands, with respect to the kinds of vegetation and the density of livestock.

-Deferred Grazing Exclusion

Deferring grazing activity for one or more grazing seasons promotes natural range land forage renovation by allowing forage species to reach maturity and re-seed the area. This typically increases plant densities, the density of plant residues in the upper soil layer, while reducing erosion and soil and nutrient export form the range lands. Supportive control of undesirable species may be needed to maximize intended benefits. In some cases, total livestock exclusion may be needed to provide soil and water quality protection or to protect valuable fish spawning areas.

-Streambank Protection/Vegetation

Streambanks that have been subject to previous erosional forces can be protected by planting appropriate riparian vegetation. This technique can reduce erosion potential and downstream water quality impacts. While reducing erosion and water quality impacts, the vegetation can also support livestock control schemes and enhance fish and wildlife habitat values. Where feasible, vegetation would be considered more preferable than fencing to limit livestock access.


Salt can be strategically located in pasture and grazing areas to facilitate even distribution of livestock and minimize overgrazing, soil erosion, and water quality impacts.

-Stream Stabilization

This BMP involves the application of stream bank stabilization techniques other than vegetation, including the selective placement of large rock, log revetments anchored to the bank, use of gabions, and other similar structural techniques. These approaches may be needed in cases where erosion problems have become so severe that revegetation is not a feasible approach.

-Critical Area Planting/Treatment

This is similar to streambank vegetation practice, but, the application is to areas not adjacent to streams. The intent is to use various kinds of tree and shrub planting or to stabilize areas that have undergone sever erosion. Supportive practices such as debris basins, contour trenching, or fencing should be considered.

-Conservation Cropping System

This BMP is applied to crop lands which involves the use of grasses and legumes in rotation with production crops. The legumes are nitrogen fixers and restore the nitrogen balance of the soils while maintaining stable soil conditions and reducing erosion. Grasses help restore soil organic content, enhance soil stabilization,and reduce erosion potential, while being moved for hay.

-Crop Residue Use

This BMP involves the use of crop residues on lands to reduce soil erosion during high runoff periods, enhance soil infiltration, and to enhance pollutant removal by crop residue filtration/absorption.

-Conservation Tillage

This is any system of tillage and planting in which at least 30 percent of the soil surface is covered by crop residues after planting. The benefits are similar to Crop Residue Use.

-Grassed Waterway

This BMP is used on crop lands to assist in the control of runoff and aid in the removal of sediment and other pollutants prior to discharge waters. Waterways are used to handle excess runoff from terraces, diversions, or natural drainage courses in a manner that minimizes flooding and water quality impacts.

-Tailwater Treatment Ponds

These are sedimentation ponds intended to remove suspended sediments and other associated pollutants prior to leaving the farm unit or prior to discharge to receiving waters. They can also be designed to provide flood storage and prevent downstream erosion caused by excessive peak flows.


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