A Unique Approach to Reservoir Restoration - 1994-95



The Students: Karrie Bolen, Chris Stiles, Robert Steele, and Brad Stanton

The Teacher: Clinton A. Kennedy

Awards: 1995 Seiko Youth Challenge West Region Semi-Finalist and Finalist - A Unique Approach to Reservoir Restoration




Reservoir Restoration


Cascade Reservoir was built in 1948, for irrigational purposes. Over the years the reservoir's water quality has been deteriorating. But it was not until August of 1993, when cattle grazing on the reservoir's shores died due to these large cyano-bacteria blooms, that the seriousness of the situation was brought to the publics attention. Because the town of Cascade's economy greatly depends on the tourism generated by the reservoir recreational attributes, finding a cure for algae-blooms became a top priority for our Advanced Biology class.

Research showed us phosphate was the limiting reagent algae feed on. Through a multitude of LaMotte tests we discovered Cascade Reservoir has an excess of phosphate even after a large algae blooms. If we could eliminate the phosphate we would effectively remove the cyanobacteria and cure our lake.

In our attempts to formulate a solution we contacted a number of the worlds leading limnologist. Through phone calls and internet communications we learned that increasing the flow rate in our reservoir could effectively flush the algae from our reservoir. Part of our group began to research this new information in more depth while the other half contacted various lake administrators that have used alum to eliminate cyano-bacteria problems. From a book written by E.B. Welch we learned the use of alum was not a practical solution because our reservoir because it is calcium poor.

Fortunately we received information on lime treatments from Dr. Ellie Prepas. Lime, which is sprayed on the surface of the lake, acts as a flocculent dragging phosphorus and algae down to depths where photosynthesis can not occur. At the same time lime forms a hydroxyapatite which will effectively cap sediments and stop internal recycling, a major problem of our reservoir.

A major draw back to this plan was the price of the continual lime treatments. What we opted to do was dump inexpensive limestone boulders into the lake. This would effectively cap the sediment and limit internal recycling of phosphate. Its only draw back was that it would not act as a flocculent and phosphorous would still be left in the water levels. Fortunately we were able to combine the technique of flushing to the limestone boulders. By flushing we could effectively remove phosphate still floating in the water and then use the limestone boulder to cap the sediments and stop internal recycling.

The lake stood calmly in the sweltering heat. At first glance the serene waters glimmered with a cool, sweet perfection, but deeper, beneath the bright reflections of the surface the lake reeked of decay. Day after burning day the waters continually cycled cyanobacteria and the beaches grew with a green, fungus like mush. The over powering smell turned away even the most ambitious fishermen. The deteriorating reservoir began to go anoxic. In August of 1993 the State was shocked when toxic water in the reservoir killed upward of 17 cattle and human contact with the lake was banned. The small community of Cascade, Idaho greatly depends on the reservoir for irrigation, recreation and electrical purposes. Therefore, as the reservoir died, so did the economy of Cascade, Idaho. The problem was out of control; it was time for the "Phosphate Family" to become involved and to lead our own investigation.

Our initial analysis led to a firm understanding concerning Cascade lake's general background. Fatmers on the North Fork of the Payette River were in desperate need of a water source that would service to their crops during the summer months. This prompted the town of Cascade to begin searching for a possible dam location. During the year 1948, the tiny town of Van Wyck became the victim of what is now known as Cascade Reservoir.

This large reservoir, which is operated by the Bureau of Reclamation, is a seventeen mile long lake with a surface area of more than 26,000 acres and an average depth of 27 feet. The reservoir was the center of recreation for central Idaho, until its vitality was affected by a number of different factors ranging from phosphate loading from an upstream sewer plant to an excessive amount of internal recycling. These factors have been a growing problem but it was not until recently that the magnitude of the lake's problems became apparent to the students of Cascade High School and the surrounding community.

We began our limnologicai investigation of the reservoir in Mr. Kennedy's Advanced Biology class. Our journey toward finding a solution for the lake began when Mr. Kennedy first introduced us to a dissolved oxygen test. Little did we know that this simple oxygen test would act as a firm foundation for many different LaMotte tests that we would run in the near future. The school's spectrophotometer would soon be used to determine the amount of phosphate in our lake. Spectrophotometers measure the amount of light blocked by the molecules in different solutions. We chose to lock up our phosphate in an ammonium molybdate color compound solution. The spectrophotometer had to be calibrated to read the maximum wavelength of the complex phosphoammonium molybdate. Once this wavelength was determined, serial dilutions were made to construct a beer's law plot. With this line graph we were able to take lake water and accurately calculate the phosphate levels in the reservoir.

In addition to the spectrophotometer we used a colorimeter from the LaMotte kit, in order to photoelectrically measure the amount of colored light absorbed by a sample of lake water. A colorimeter is basically the same as a spectrophotometer but the calibration of the machine is pre-set. Again we resorted to the water test kits to run such tests as ortho and total phosphate, pH, and nitrate. The results of the phosphate tests were lower than expected, considering the media's implication that the phosphate levels in the reservoir were at an all time high.

Through further research however, we discovered that we were conducting phosphate test after the fall algae blooms. The phosphate levels appeared low because the cyano-bacteria rely on phosphate to survive. Since phosphate is the limiting reagent for cyano-bacteria the fact that any was left in the reservoir proves that there was an excess amount of phosphate before the algae bloom occurred at fall turnover. Turnover occurs when the all water in the reservoir reaches 4 degrees. This allows the sediments that are resting in the water column to mix freely. Turnover is considered bad because nutrients are brought to the top of the reservoir where the sun is able to penetrate, creating algae blooms.

Many factors determine the intensity of the cyano-bacteria blooms; temperature, wind, exchange rates, dilution, sun penetration, nitrogen, and phosphate levels. The only factors that can be controlled are phosphate, dilution, and flushing. In order to control the algae blooms, we must limit the amount of phosphate that is brought in through the reservoir watershed. This idea of controlling phosphate set the stage for the project in which our group was about to begin.

In order to better understand the reservoir's current limnological problems, as well as formulate possible solutions, we contacted Dr. Wayne Carmicheal of Wright State University, the worlds leading authority on cyano-bacteria. On October 17 we embarked on the first of many communications through cyberspace. Dr. Carmicheal was more than willing to assist us with our project but due to the fact that he was obligated to other commitments, he recommended that we contact his colleague, Dr. Gary Jones, in Australia. Both of these men are the world's leading researchers of blue-green bacteria. According to Dr. Carmicheal, Gary Jones and his Australian company, CSIRO, had found ways to cure the cyanobacteria problems in Australia.

Dr. Jones stated that the ideal growing conditions in Australia produced incredible algae bloom to occur. According to Gary Jones if we are able to increase the flow rate in our reservoir then the cyanobacteria would suffer from lack of sunlight and oxygen. This would restrict the algae from flourishing to toxic levels. Dr. Jones' proposal was currently being looked at by the DEQ, so we moved on to possible chemical treatments.

Two of our group members visited the Cascade Bureau of Reclamation in order to research snow pack readings to predict this years run off and flow rates, while the other two spent quality time reading books and contacting various lake administrator's that have used alum and lime to eliminate cyano-bacteria from their local reservoirs. Browsing,through a book called. The Ecological Effects of Waste Water, by E.B.Welch, we discovered that a reservoir in Washington had done intense studies using alum. Using an atlas from our schools library, we located this lake known as Long Lake, and contacted the local Bureau of Reclamation office. The Long Lake that we discovered had not only undergone a name change to Billy Clap reservoir, but also had been transformed into an irrigational reservoir. Through further examination we also discovered that' there were several Long lakes in Washington, and this reservoir had not undergone any alum treatments. This lake was obviously not what we had in mind.

We again consulted The Ecological Effects of Waste Water. to locate the alum-treated Long Lake. After locating the correct Long Lake, we contacted the supervisor of lake operations. The supervisor of the correct Long Lake gave us the number for E.B. Welch at the University of Washington, who was elated to see high school students doing such research. As it turned out, E.B. Welch had written a book primarily about lime and alum treatments. We went down to our local library and ordered the book, Restoration and Mananement of Lakes and Reservoirs through the inner-state library loan.

After reading through all of the information that we obtained about alum, we decided to take our knowledge to Dewey Worth at the DEQ office in Cascade. Again, alum treatments had been options for Cascade Reservoir, but due to the fact that our reservoir is calcium poor, alum was not a practical solution. Information we received also illustrated many other phosphorus inactivates such as iron and calcium. Iron compounds function primarily on pH factors. Acidic conditions in Cascade Reservoir would necessitate a technique such as aeration or artificial circulation to prevent the breakdown of oxidized microzone, or an increase in pH. The microzone is the layer at the bottom of the reservoir, where all of the chemistry of the lake takes place.

We became very frustrated and decided to once again consult, Dr. Carmicheal. To our surprise Wayne Carmicheal's colleague, Dr. Ellie Prepas, had done extensive research on lime treatments. This boosted our spirits and gave us a second wind. Dr. Carmicheal Emailed Ellie Prepas and shortly after a package of requested information arrived. The lake that Ellie and her team used to do lime experiments on in Canada was similar to our reservoir in Cascade. From this point, we spent many hours trying to find a practical method to use lime to limit the amount of phosphate available as well as stop internal recycling.

It had become apparent to us through our research that a large percentage of our lake's' excess phosphate was a result of internal recycling. Phosphate rich water was being transported directly into the reservoir from many external sources. Although there have been many efforts to reduce external loading of phosphate the problems seem to increase as years pass. The McCall sewer plant has become aware of the phosphate that their plant releases into the Payette River. Local authorities still believe that the McCall sewer plant is responsible for the high levels of phosphate in Cascade Reservoir, even though only 11 % of the phosphate accounted for in the lake originates from the upstream plant. Other external sources of phosphate include agricultural practices and leaky septic tanks from shore-side residency's.

External phosphate loading results in cyano-bacterial blooms during the summer months. Once these algae die, they sink to the bottom of the reservoir as detritus, effectively taking the phosphate locked up in their biomass with them. Year after year the dying algae repeat the same cycle thus adding to the phosphate rich sediments and creating a layer of phosphate and bio mass near the bottom of the reservoir. During fall and spring turnover, when free mixing occurs between the reservoir layers, this underlying phosphate and biomass is cycled back into the water column. After many years of this repetitious cycle the phosphate that is Iying on the bottom of the reservoir in large masses and high concentrations creates a greater problem than external loading.

Another problem also occurred with this high phosphorus concentrated water Iying at the bottom of the reservoir. When lower phosphate concentrated water is brought into the reservoir, the higher concentration in the sediments diffuses years of trapped phosphate into the less concentrated water.

This research has influenced us to believe that the majority of the reservoir's problems are a result of internal recycling. We feel that internal recycling must be controlled in order for the reservoir's problems to imp, rove.

A letter from Janice Burke, Ellie Prepas' technologist, gave us late breaking news on lime treatments. According to this letter, lime reduces the biomass of algae in the water column in these two ways. 1.) Lime is sprayed on to the lake surface in a slurry, and because lime is particulate, it settles to the lake bottom. As the lime flocculates, it drags phosphorus and algae down to depths where photosynthesis is no longer a possible option. 2.) Once at the bottom, lime forms a complex called hydroxyapatite, which is insoluble. This means that less phosphorus will be released from the bottom sediments into the water. Without this prime phosphate source, algae blooms are greatly reduced as phosphates becomes the limiting reagent. Lamentably, due to the size of our reservoir, the lime treatment would need to be reapplied too often, causing a large price tag for taxpayers.

This problem caused us to look at the use of limestone boulders instead of lime spray. Because limestone is much cheaper it would not be such a heavy expense. Unfortunately the trade off was in efficiency. Limestone would not act as a flocculent so phosphorous floating in the water would not be removed, yet at the same time the calcium from the lime would form a hydroxyapatite, effectively capping the sediment and strongly limiting internal recycling. In order to make up for the loss of lime as a flocculent we decided to combine the limestone treatment with the aid of flushing.

Through information given to us by Dr. Jones, we discovered that increasing the flow rate through a stream or pond would help to reduce the build up of blue-green algae. Unfortunately, because we can't control the amount of water entering the reservoir from mountain run off, we could not control the flow rates through the reservoir. The only factor we could control was the amount of water leaving through Cascade Dam. This meant that controlling the flow rates through the reservoir was not possible, but we could flush by increasing the amount of water leaving the reservoir. We contacted Rick Wells at the Snake River Soil Conservation Office who informed us that controlling the amount of water passing through the dam was not as simple as just opening the dam and letting out more water. A variety of factors go into determining when and how much water will be let out of the reservoir. We can not completely flush the reservoir at any time because of private water rights and contracts with local agencies, agriculturists, and environmentalists. The water in the reservoir is necessary for salmon runs, recreation, hydroelectric power, and most important, irrigational needs.

After a conference call to Mr. Rick Wells we discovered that the greatest water demand comes from down steam agriculturists who have special contracts guaranteeing enough irrigation water. Mr. Wells suggested we contact Payette Ditch Company, who is in charge of mediating between farmers who need water to irrigate their fields, and Cascade Dam. From the Ditch Company we learned that the amount of water the farmers need can not be determined until the years final snow pack surveys are finished. Then the dam coordinates the farmers needs with the needs of others.

At this point we began looking into the snow pack levels in the lakes 350,000 square acre drainage area. We visited the Cascade Bureau of Reclamation in order to determine where the snow pack survey sites were located and what the predicted snow pack levels were for this year. We found most survey sights are unmanned stations in the high mountains surrounding the reservoir. Snow levels are automatically recorded and sent by satellite to Rick Wells in Boise who compiles an annual report. We were able to obtain copies of last years report as well as the predictions for this year. It was determined that it would take 120% of a normal winter's precipitation in order to fill the reservoir to normal levels. Snowtell, a computerized snow pack measuring service, was predicting 250% of normal. This was enough run-off to carry out our proposed flushing project. It was time to begin collecting hard data on just how much total phosphate was locked in biomass in our lake and when the best time for flushing would be.

Each week we used HACH and LaMotte test kits to run total phosphate tests on water we gathered from a variety of testing sites around the lake. These tests required at least 30 minutes of boiling the water sample in a solution with sulfuric acid in order to break down the phosphate locked in the biomass and took much of our after school time. So it wa,s disappointing when the test did not give a promising out look on the workability of our project. Low levels of total phosphate indicated that there was minute amounts of phosphate locked in biomass. We took the problem to Dewey Worth at the Department of Environmental Quality, who explained that low phosphate levels were to be expected considering the time of the year, which was late fall-early winter.

During the summer the cyano-bacteria use the external source of phosphate to grow, locking it up in their biomass. When the algae dies it sinks to the bottom of the reservoir, taking the locked up phosphate with it. The top of the lake then cools in the early fall and the warmer water on the bottom rises causing mixing between the layers, bringing to the surface the biomass that has settled during the summer. Fortunately in early fall the biomass has not had time to break down and the phosphate is still locked up. The algae have no phosphate readily available to grow so only minor blooms occur. Within a few weeks the biomass resettles, and for the remainder of the winter there is no mixing between the levels. It was during the late fall, after the biomass has settled out of epilimnium that we ran a series of tests. We ran these tests using deep water samples instead of surface samples, and found higher total phosphate. These results supported the theorized conditions during fall turnover.

As far as determining when the best time to flush is concerned, we compiled what we had learned and concluded it would be best to flush just before spring and possibly fall turnover. This was due to the fact that just before spring turnover the biomass has had all winter to settle and break down. Because our dam drains from the bottom of the lake we could flush the phosphate while it was concentrated in the hypolimnium. If we waited until after spring turnover the phosphorus would be distributed and it would take more draining to eliminate the same amount of phosphate. We could flush, again, just before fall turnover for the same reasons. The biomass that died during the summer and settled to the bottom could be flushed in a concentrated amount.

Flushing during the winter and summer mouths would be less efficient. In the summer new algae blooms continually add to the build up of blue-greens and most of it does not die and settle until late fall. Flushing then would not significantly reduce the total phosphate. If we flushed during the winter not all of the biomass would have settled and we would only get hypolimnetic water, leaving much of the biomass still floating in the mesolimnuium.

The fact that biomass settles hindered our project more than it helped. Settled biomass becomes trapped in the lakes sediment. Even if we could flushed out all the biomass and the phosphate from the hypolimnium of the lake we would still not be able to flush out phosphate locked in the sediment. When the clean run off water refills the lake, it would have a lower Phosphate level than the sediment and diffusion would occur, releasing several years locked phosphate back into the lake at once. We decided the best solution was to flush the lake and then place large limestone boulders in critical locations which would release calcium to lock up any remaining phosphate and seal the sediments. Calcium hydroxide can be added to a reservoir from allochthonous sources, or produced in hard water lakes during periods of CO2 uptake during photosynthesis, as follows:

Ca(HCO3)2 = CaCO3 (s) + H2O +CO2

At higher levels of pH Ca3 + P, hydroxyapatite forms as follows:

10 CaCO3 + 6(HPO4)2 + 2H2O = Ca 10 (PO4)6 (OH)2 (s) + 10 HCO3


In the book Restoration and Management of Lakes and Reservoirs, we discovered that Hypolimnetic withdrawal has been tested on 18 different lakes and reservoirs. Maximum hypolimnetic TP concentration decreased in all but one lake and epilimnetic TP decreased in 8-12 of the lakes where data was available. The reduction in hypolimnetic TP is a direct effect of flushing while epilimnetic reduction in TP is an indirect effect. This demonstration that entrainment of P from hypolimnion to epilimnion was reduced. The effect of withdrawal on epilimnetic TP was most significant as a function of grand total TP rather than annual export, either as total or areal. The advantages of hypolimnetic withdrawal are as follows: 1 ) evidence of effectiveness in a large fraction of cases, and 2) potentially long term and even permanent effectiveness. In most cases, hypolimnetic DO increased, resulting in a decrease in the anoxic volume and the days of anoxia. Internal P loading usually decreases with flushing alone but with the aid of limestone internal recycling will be almost eliminated.

Once we had learned about the lime and flushing, we sat down and tried to apply all of this information to the restoration of Cascade Reservoir. We discovered that the Seven Devils Mountain range has a fairly large limestone content. Our minds began to fill with glorious thoughts as a proposal was finally within reach for the "Phosphate Family". If we were to collect large boulders from this mountain range and dump them into the reservoir, not only would it add calcium and form hydroxyapatite with calcium and phosphate, it would also add fish habitat. The calcium from the boulders will initially release calcium to the bottom of the reservoir making it available for bonding with the phosphorus rich sediment.

Once the limestone boulders are added if the lake, by chance, does go temporarily anoxic, the phosphorus bonded by other means such as iron and aluminum will not break apart due to the basic conditions created by the limestone.

After holding a second small group meeting with Dewey Worth, head of the local DEQ, we were elated to find out that there were no major problems with our proposal. Two minor setbacks were that hydroxyapatite may become insoluble in our lakes acidic conditions, and due to our reservoir's large size, the amount of limestone to reduce immense amounts of phosphorus would be enormous. Cascade reservoir happens to be slightly acidic, which might constitute a problem concerning hydroxyapatite solubility. However, when the limestone is added to the reservoir it will cause the pH of the water to rise, thus keeping the hydroxyapatite bonded. Still, the amount of limestone needed to reduce the massive amount of phosphorus that the reservoir contained would be extremely large, however these boulders will be in the reservoir for many years.This is to the communities advantage because calcium will be constantly released without human intervention. After examining our material on flushing we contrived that if we were to flush the bulk of the phosphate out during spring turnover, the limestone could successfully cap the remaining phosphorus in the underlying sediments.

The most exciting part of our project was that while researching for possible solutions for Cascade Reservoir, we were given the chance to talk to the leading researchers on our subject. Although these people were extremely busy, they still found time to look at our specific situation and offer any information and assistance they could. Not only did we talk to leading researchers, but we were also connected to their colleagues who also took time to help with our problem. The first time we were able to use internet was amazing to all of us. Communication became a large factor in our project and by using internet our project was able to advance at rapid speeds. Our group was able to send and e-mail message to Australia and have a response within a few days.

When we first began looking into options for the Seiko Youth Challenge, the group as a whole had a problem speaking to gods of the algae world. As time progressed, however, we were able to call Wayne Carmichael and Dr. Jones without hesitation. Before we knew it, we were calling authors of books and the leading researchers of cyano-bacteria. These people began referring us to their colleagues and before long our phones began ringing constantly. It was amazing to us that such powerful sources would take interest in students and their concerns for the environment. With the world's leading researchers backing us, we were able to present our project to local authorities who are now considering a multitude of alternatives for the reservoir.

The work we've done will have a long term effect on the reservoir, as well as changing the way our science department at Cascade High School is viewed. We plan to continue our effort in this on going project in hopes that our work will lead to a safer healthier environment for everyone.


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