Mirror Pond Rehabilitation Study 1981

Mirror Pond Rehab Study 1981 final_Page_01

 

MIRROR POND REHABILITATION

August, 1981

Diagnostic-Feasibility Study
U.S. Environmental Protection Agency
Clean Lakes Program

Prepared for
The City of Bend
and the
Bend Parks and Recreation District

Winzler and Kelly
Consulting Engineers
1730 S.W. Skyline Blvd.
Portland, Oregon 97221

Clark and Joyce, Inc.
Consulting Engineers
1132 N.E. 2nd Street
Bend, Oregon 97701

ACKNOWLEDGEMENTS

This Mirror Pond Rehabilitation Study was financed by the City of Bend, Bend Metro Park and Recration District and Oregon Department of Environmental Quality through a grant  provided by the U.S. Environmental Protection Agency.

The following people participated in the study and provided valuable input:

Arthur R. Johnson, City Manager
Thomas Gellner, City Engineer
Vince Genna, Bend Metro Park & Recreation District
Peggy Sawyer, Bend Chamber of Commerce
Dick Nichols, D.E.Q.
Peter Ressler, D.E.Q.
Mirror Pond Committee Members
Harold Baughman
Robert Bristol
Reed Nelson

I. EXECUTIVE SUMMARY

A. Location and Access

Mirror Pond is located in the developed portion of Bend (see Figure 1) . . It stretches from the Pacific Power & Light Co. Dam to Galveston Avenue, a distance of about one mile. Over the years, private homes have been developed along the pond’s edge, primarily on the westerly side of the river. Drake Park fronts most of the pond on the easterly side of the river, and three smaller parks, Harmon· Park, Pageant Park and Brooks Park border portions of the pond on the westerly side. All of these parks provide public access to the pond area. Access to the parks is over public streets and walkways located adjacent to the parks.

B. Diagnostic Study

Siltation of Mirror Pond has curtailed much of the former recreational use of the pond. In addition to  reducing depths, siltation has encouraged excessive growth of aquatic vegetation that further interferes with boating, fishing, and swimming and creates unpleasant odors at times. Promotion of vegetative growth is related to the shallow depths, which provide sufficient light at the bottom to encourage seedling growth. The purpose of this investigation, funded by a Clean Lakes Program Phase I grant from the U.S. Environmental Protection Agency, is to recommend methods of rehabilitating the pond in order to restore beneficial uses.

Water quality data assembled for this study reveals no drastic increase associated with the Bend urban area in any water quality parameter that could contribute to eutrophication. Biological oxygen demand levels above and below Bend do not indicate gross organic pollution, but sufficient levels of nitrogen and phosphorus are available in the Deschutes River upstream from Bend to promote eutrophication.

Sufficient historical data to indicate sedimentation rates in the pond is lacking. Sediment chemistry analyses, provided by the City of Bend, reveal that sediment nutrient concentrations increase in the deeper sediments.

No single source or land use can be blamed for eutrophication or sedimentation problems in Mirror Pond, since the water quality problem in the Deschutes River is related to overall intensive use of the watershed. Likely sources of sediment and pollutants include:

  • natural sediment load
  • faulty septic systems
  • agricultural runoff
  • sediments from failed riverbanks
  • turf fertilization

Mirror Pond acts as a settling pond to accept nutrient-enriched sediment from all of these sources. Riverbank failure, aggravated by artificial water level fluctuation and power boat wakes, is widely believed to be the major sediment contributor. Point sources of sediment include historical upstream uses of the river as a log pond and ongoing influx of road cinders from City of Bend storm drains.

C. Feasibility Study

Rehabilitation efforts will be directed at resolving the primary problem – siltation and the resulting shallow water depths. Some alleviation of the secondary problem of aquatic plant growth is expected, but dredging beyond the depths allowed by funding would be necessary to achieve a long-term suppression of plants. The availability of nutrients in sediments and water is not susceptible to control within the limits of this program, since the sources of nutrients are dispersed.throughout the watershed.

Bucket and hydraulic dredging methods were investigated. Based on lower cost, fewer turbidity problems, and lesser impacts on· park and residential areas, hydraulic dredging was selected. The floating hydraulic dredge employs a pump with the suction inlet behind a rotating cutter that transforms bottom sediments into a slurry. A series of four or five booster pumps will be used to pump the slurry by pipeline to the disposal sites, where settling ponds will dewater the sediment and clarify the tailwater before return to the river.

Alternative projects were identified by dividing the project area at the footbridge into areas designated as “Newport” (north) and “Galveston” (south) (see Figure 9). The dredging depths considered were 5 feet and 8 feet, result,ipg in the following possible project components, shown with their construction costs (engineering and administration would add 15 percent):

Area · Dredge Depth · Cost
Newport · 5 feet · $128,500
Newport · 8 feet · $242,900
Newport · 8 feet & Galveston · 5 feet · $346,800
Newport & Galveston · 8 feet · $389,800
Newport & Galveston · 5 feet · $232,300

The apparent best project, as determined by discussions with the City of Bend, the Bend Parks and Recreation District, and the Mirror Pond.·(Citizens Advisory) Committee, is to dredge both the Newport and Galveston areas to 5 feet (see Figure 10). This will allow resumption of recreational use of the lake and provide some measure of vegetation control. Because of cost considerations, the construction of new islands using dredged material, suggested in earlier discussions, has been deleted. The material will be dredged as uniformly as ‘possible to obtain maximum project benefits.

The selected project will generate about 60,000 cubic yards of dredged material. Two upland disposal sites were investigated. The chosen site, designated Site B 2, is located about 5600 feet south of the Galveston.Avenue bridge, with a capacity of 82,800 cubic yards. (See Figure 11.) Investigations of sediment size and chemistry suggest that an effluent of acceptable quality can be returned to the river after settling and final clarification in a settling. basin. Property owner permission will be required for use of the disposal site, as well as for portions of the route for the temporary dredge pipe. Disposal site property owners have been contacted, and they have indicated a desire to receive the dredged material for ‘fill.

Project funding is expected to be provided by equal contributions from the City of Bend and a Phase II Clean Lakes Program grant from the U.S. Environmental Protection Agency, which will be pursued at the conclusion of this Phase I study. Dredging is tentatively scheduled.to take place during the spring of 1982.

A post-project monitoring program is required by Clean Water Program rules. Since DEQ already monitors water quality at a number of stations in the vicinity, and since the primary objective of the project is depth increase, the monitoring program will emphasize sedimentation rates and effectiveness in aquatic vegetation suppression. Simultaneously, the City of Bend will pursue additional programs to protect the pond, including cinder collection by storm drain catch basins, ·completion of the City sewage collection and treatment system, and cooperative programs with other agencies to control upstream sediment and pollution sources.

II. DIAGNOSTIC STUDY

A. Location and Access

Mirror Pond is located in the developed portion of Bend (see Figure 1). It stretches from the Pacific Power & Light Co. Dam to Galveston Avenue, a distance of about one mile. Over the years, private homes have been developed along the pond’s edge, primarily on the westerly side of the river. Drake Park fronts most of the pond on the easterly side of the river, and three smaller parks, Harmon Park, Pageant Park and Brooks Park border portions of the pond o.n the westerly side. All of these parks provide public access to the pond area. Access to the parks is over public streets and walkways located adjacent to the parks.

Boat ramps are not provided along· the waterfront. Motors are prohibited on Mirror Pond, and because of limited access, pond use is limited primarily to row boats, canoes and inflatable rafts.

B. Geological Description and Soils

The geological history of the Deschutes Water Basin is one of recurring volcanic activity, dating back nearly 40 million years. The Newberry Volcano was the last major volcanic activity affecting the basin. _Basalt, the most common material erupted from the volcano, forms much of the surface of the basin. Ash from the Newberry Volcano and other volcanoes near Broken Top and South Sister also covers large areas of the basin. The Deschutes River flows through these volcanic deposits of basaltic rock, ash, cinders and pumice before entering Bend.

Soils in the Deschutes basin are developed from basaltic material, pumice, ash and glacial till. The major soil associa­tion is Shanahan, which consists primarily of loamy sand. The area is dominated by cold, excessively drained ashy soils on level, moderately steep and steep uplands These soils are not suited for agricultural uses unless supplemented with other fine soils and organic material.

Mirror Pond was created on the Deschutes River by the construction of a power dam. The impact on groundwater created by the pond is .insignificant compared to the Deschutes River, which. flows over miles of fractured basal tic rock upstream from the City of Bend.· If any exfiltration did occur when the pond was originally created, the sediment deposits have probably reduced the rate o.E exfiltration over the years.

The ground elevation” in Bend is 3,600 feet. The drainage basin rises in a southerly direction to elevation 6,600 feet 50 miles south· of Bend. Between Benham Falls, 10 mile.s south of Bend, and Mirror Pond, there .is approximately 1,000 feet difference in elevation. Numerous rapids and falls are located on the river within these limits. South. of Benham Falls, there are fewer rapids and the slope is more uniform to the upper end of the drainage basin.

Project Location. Figure 1
Project Location. Figure 1

C. Population Description

In 1978 it was estimated that 33,’000 people live in the Bend urban area, representing about 66% of the county population. The area has experienced one of the highest rates of growth in the state during the last five years.

The community enjoys the benefits of the park system adjacent to Mirror Pond in Bend. Many organized activities are coordinated by the Park and Recreation District in the parks and on the pond. The primary beneficiaries of these activities are local residents. In addition to the organized activities, the people seek the leisure activities and the beauty of the area which the pond and park system provide. Studies show a higher than average number of retired people residing in the County. It is surmised that retired people seek health, recreation, and other social activities that are provided in the County.

It is difficult to project the population increase for the County because of the rapid rate of.increase experienced during the last few years. It is anticipated that the rate of growth wil 1 decrease in the future, but projections of a 4 .5% annual increase have been made by the County in the Comprehensive Plan.

Mirror Pond Rehab Study 1981 final_Page_13
The population growth for Deschutes County is shown in Figure 2.

Historical Lake Uses

It is impossible to address the historical uses of Mirror Pond without also discussing· the adjacent park uses, because the two function as a single entity.

In the early days,. the acreage along the east bank of the Deschutes River, a swift flowing river until a power dam was constructed in 190;, was owned by The Bend Company.

The Hunter Brothers, owners of The Bend Company, had purchased from A.M. Drake, founder of the City, the power company, an irrigation company, a sawmill, timber stand and the acreage along the east side of the river.

The Bend Company held the east-side property in.reserve for future commercial or industrial development, and operated a lumber mill on the west side of the river. The east-side area remained a sort of “no mans land” through the pioneer days.

In 1921, The Bend Company sold the acreage along the east bank of the river to the City of Bend. The City designated the acreage as a park and named it Drake Park.

Mirror Pond provided an ideal place for youngsters to fish in early days. It remains a good place for them to fish, and an annual fish derby is held, usually during the opening days of the fishing season. ·

Bend residents decided in the early 1930’s to revive the traditional Fourth of July celebration to keep people in town over the holiday. This was the beginning of the Bend Mirror Pond Pageant, which started on July 4, 1933. The Pageant featured floats drifting in Mirror Pond. Each year more extravagant. displays were made for the event. Lighted arches were placed in the river and served as a portal for the floats. The show attracted as many as 10,000 people to the event.

Eventually the Pageant became too costly for the City. In addition, the siltation of Mirror Pond made it increasingly difficult to float any unit along the park banks. In 1965 the annual Bend Mirror Pond Pageant fetes ended.

Long-time residents tel.l about swimming in Mirror Pond. The water was cold and deep. Eventually though, swimming became more hazardous as debris and sediment accumulated in the slack waters. Concern arose that swimmers would become entangled in the weeds that were growing from the bottom of the pond. The City fathers lowered the pond water level and attempted to remove the weeds by pulling them by hand, usually from rafts and boats. Today, swimming is prohibited in Mirror Pond by City Ordinance.

Drake Park and Mirror Pond remain the focal point for programs and activities sponsored by the Bend Park and Recreation District and various civic groups. The pond itself is seldom
used in conjunction with these activities because of its shallow depth in areas adjacent to the park.

The Bend Park and Recreation District provides boating activities for teenagers and adults as part of the summer recreation program. This program is limited in scope because of the danger of boating on the swifter water where sufficient depth remains for boating activities. Water safety programs, usually conducted closer to. shore in calmer water, are difficult to provide on Mirror Pond today.

The pond provides a habitat for many species of waterfowl. Most of the fowl are wild, but hand feeding has encouraged· some of them to become tame. They provide much enjoyment to the young and old visitors to Mirror Pond. Protected nesting places allow them to replenish their numbers each year. To many people, the waterfowl are the greatest attraction in the area.

E. Comparative Recreational Value

Mirror Pond provides a type of use and enjoyment that could only be provided by a lake within the urban area. Its accessibility to people in the community provides an attraction one can enjoy without having to travel great distances. Lakes, rivers· and ponds historically attract people for leisure and recreation. An attractive lake within an urbanized area provides beauty and enjoyment that the whole community can enjoy.

F.

G.

H. Land Use and Eutrophication: Point and Non-point Sources

From the previous discussion of Deschutes River water quality above and below Mirror Pond, it is evident that no single source or land use can be blamed for eutrophication problems in Mirror Pond, since the water quality problem in the Deschutes is related to overall intensive use of the watershed. Land uses in the surrounding watershed are illustrated in Figure 4. Figures 5 through 8 illustrate the condition of the Deschutes River in the vicinity of Bend with respect to a number of important water quality parameters. This series of figures was extracted from the Oregon DEQ’s 1978 Statewide Assessment of Non-Point Source problems.

Examination of the land use map shows that as the river flows toward Bend, it likely receives sediment and pollutants from a wide variety of sources, including:

  • natural sediment load
  • faulty septic systems
  • agricultural runoff-manure, sediments, and fertilizers
  • sediments from failed riverbanks
  • turf fertilization-residential and park

Mirror Pond acts as a settling pond to accept nutrient-enriched sediments from all of these sources. Riverbank failure is widely believed to be the major sediment contributor. Riverbank erosion caused by water level regulation has been reduced in recent years by slowing the rate of water level fluctuation.

A recent paper by McCammon (1980) postulates other causes for sedimentation from eroded banks. Low winter flows subject the exposed pumice banks to frost heave. Higher summer flows tend to move this material downriver. The low river gradient in this stretch of the river, however, results in rapid deposition. The river, in turn, responds during high flows by lateral migration with further bank cutting. The extent of the streambank cutting has been documented in a Photographic Streambank Inventory conducted by Century Testing Laboratories for the U.S. Forest Service in 1978.

Power boat activity, in particular, has been demonstrated by Garvin (1977) to aggravate the bank cutting and sediment movement problem in the stretch of the Deschutes River between the Wickiup reservoir and Bend. Garvin concludes from sample observations that “The sediment produaed by boats alone during less than 1/3 of the year is estimated to be 28 pe:tcent of the total sediment produced. However, sediment produced by boating causes the sediment load of the river to be increased by 39 percent.” The paper summarizes various regulations that could be implemented to
reduce power boat impact.

[SlideDeck2 id=3963 ress=1]

Other sources of pollution are considered point source discharges and include man made facilities or operations that result in increased sediment or debris loading of the waters.

The power dam constructed in 1909 created Mirror Pond. The slack water in the pond at lows particles carried by the river or discharged into the pond to settle to the bottom. The depths of the sediment in the pond, varying from 2 feet to over 8 feet, have been accumulating since the dam was constructed.

The river was used as a log pond for many years by the Brooks and Shevlin-Hixon logging companies. A dam was constructed south of Mirror Pond in 1916 at its present location near the railway trestle. “Brooks’ logs were stored on the east side of the river and Shevlin-Hixon logs were stored on the west side. Log booms were used to control the operations. The logging operations probably resulted in dirt and debris being deposited in the river. Some of the material may have washed over the dam and into Mirror Pond, but most of the material settled above the mill pond dam in the slack water. In 1975 a mill pond was constructed on the east side of the river. This pond is separated from the river and no dirt or debris enters the river from the logging operations.

The Bend Company operated a sawmill for many years on the west side of the river where Harmon Park is now located. Available records and pictures do not indicate that The Bend Company used Mirror Pond as a log pond, but debris probably washed into the pond. This is no longer a concern, because the mill was never reconstructed after it burned to the ground.

Additional sources of sediment are from storm drains discharging runoff from developed portions of Bend. This runoff carries silt, debris and cinders from the developed areas directly into the river. This source is small in comparison with the upstream erosive action. It is estimated that 50 to 100 cubic yards of cinders wash into Mirror Pond annually through the City storm drain system. If sedimentation has been uniform since the dam was constructed, this represents about 5% of the source. This is a source, however, that is most apparent to the public, and action should” be taken to reduce sediment from this source.

I. Fish and Wildlife Considerations

Conversations with the ‘Bend office of the Oregon Department of Fish and Wildlife reveal that Mirror Pond has an important function in providing wildlife habitat.within an essentially urban area.

The most visible wildlife component at the pond consists of waterfowl, including ducks, geese, and songbirds in various degrees of domestication. Particularly important to the waterfowl are the islands in the southern part of the pond, which provide for the birds nesting habitat secure from domestic and wild predators and people.

Mammals associated with Mirror Pond include primarily mink, raccoon, and otter. Removal of vegetation may reduce cover for these animals, but they are sufficiently mobile to relocate in the abundant habitat located nearby outside the urban area.

Fish species include resident species such as brown trout, whitefish, roach, and rainbow trout (stocked), and migrators such as sockeye salmon and an occasional Coho from Wickiup Reservoir.

Important invertebrates include the freshwater shrimp, crawfish, and various aquatic insects. Crawfish are utilized by residents as food and bait.

The primary wildlife issues with respect to dredging in Mirror Pond include:

Full Document: Mirror Pond Rehab Study 1981 final