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A Lake Susan Erosion AGENDA CHANHASSEN CITY COUNCIL MONDAY, OCTOBER 13, 2003 CHANHASSEN MUNICIPAL BUILDING, 7700 MARKET BOULEVARD 5:30 P.M. - CITY COUNCIL WORK SESSION, COURTYARD CONFERENCE ROOM Note: If the City Council does not complete the work session items in the time allotted, the rentaining items will be considered after the regular agenda. A. Update on Lake Susan Schedule for Lakeshore Erosion Control. 2004 Budget Presentations: 1) Community Development 2) Fire Department 3) Park & Recreation Department Co Update on Strategic Plan, Economic Development. (This discussion will take place following the EDA meeting which is being held after the Regular Council meeting.) 7:00 P.M. - REGULAR MEETING, CITY COUNCIL CHAMBERS D. Invitation to Halloween Party, October 25. CALL TO ORDER (Pledge of Allegiance) PUBLIC ANNOUNCEMENTS CONSENT AGENDA All items listed under the Consent Agenda are considered to be routine by the city council and will be considered as one motion. There will be no separate discussion of these items. If discussion is desired, that item will be removed from the Consent Agenda and considered separately. City council action is based on the staff recommendation for each item. Refer to the council packet for each staff report. Approval of Minutes: - Joint City Council/Commission Meeting Minutes dated September 15, 2003. - City Council Work Session Minutes dated September 22, 2003 - City Council Summary & Verbatim Minutes dated September 22, 2003 Receive Commission Minutes: - Summary & Verbatim Planning Commission Minutes dated September 16, 2003 bo Arboretum Business Park 6th Addition: 1) Approval of Final Plat. 2) Approval of Construction Plans & Specifications and Development Contract, Project 03-08. MEMORANDUM CITYOF CHANHASSEN 7700 Market Booievard PO Box 147 Chanhassen, MN 55317 Administration Phone: 9522271100 Fax: 952 2271110 Building Inspections Phone 952 2271180 Fax 952227 i190 Engineering ?:or,e: 9522271160 Fax~ 952227.1170 Finance Pl~c)r/e 952 2271140 Faxz 952 2271110 Park & Recreation Prlone 952 227.1120 Fax: 9522271110 Recreation Center 2310 Cou!~er Boule,~ard Pi~one: 9522271400 Fax 9522271404 Planning & Natural Resources Fax: 952 2271110 1591 Park Road Phone: 9522271300 Fax: 9522271310 Senior Center Phone 952 2271125 Fax: 952.2271110 Web Site ww~, ci ci~anhassen mn us To; From: Date: Re: Todd Gerhardt, City Manager Lori Haak, Water Resources Coordinator~ October 1, 2003 Lake Susan Erosion and Delta BACKGROUND The Chanhassen City Council directed staff to continue cooperating with the Riley-Purgatory-Bluff Creek Watershed District (District) to address erosion around Lake Susan in order to: 1. Protect existing infrastructure (sanitary sewer, trails) in riparian areas; 2. Protect property; and 3. Preserve lake water quality. The City Council has also been approached by residents regarding the delta at the inlet of Riley Creek into Lake Susan. The residents have expressed concern that the City's Lake Susan Regional Pond Reconstruction Project contributed a large amount of sediment to the lake, specifically the delta. This memo provides a tentative schedule for the reestablishment of the shoreline on Lake Susan, as well as a discussion of the delta at the inlet of Riley Creek into Lake Susan. Following this meeting, staff will send a letter to the Riley-Purgatory-Bluff Creek Watershed District to request cooperation by means of a financial contribution to the project. PROPOSED STABILIZATION Riprap with dormant staking is currently the method under investigation for use along the city trail on the northern shore of Lake Susan. A typical cross- section was designed by the District Engineer and was used to provide a preliminary estimate of the cost to stabilize the northern shore of Lake Susan. The estimated cost is approximately $160,000 for 1000 feet of shoreline. The District Engineer indicated that the District Board of Managers would likely be willing to contribute District funds toward a bank stabilization project on Lake Susan. In order to secure these funds, the District will require The City of Chanhassen o A growing cornmunity with clean lakes quality schools, a charming downtown thriving businesses, winding trails and beautilul parks A great place to iive work and play Todd Gerhardt Lake Susan Erosion October 1, 2003 Page 2 of 3 a request from the City explaining the scope of the project, the estimated cost and the amount of funding requested from the District. PRIVATE PROPERTY In addition to the shoreline stabilization project on public property, the City will organize neighborhood meetings to discuss options for stabilization on private properties and to provide a limited amount of technical expertise related to project design and installation. The City will encourage the use of native vegetation for shoreline stabilization where practical. It is anticipated that private property owners will be responsible for the costs associated with any improvements on their properties. RILEY CREEK DELTA The City has received a number of calls regarding the sand/silt delta in Lake Susan where it receives water from Riley Creek. There is a misconception that a large amount of the sediment in the delta was contributed by the Lake Susan Regional Pond Reconstruction Project that was completed this summer. The City worked with the Carver Soil and Water Conservation District (Carver SWCD) to address erosion and sediment control for the project, specifically with regard to the pond dewatering process, prior to project construction. A number of measures were implemented prior to construction to ensure that Lake Susan would not receive sediment as a result of the construction process. These measures included: 1. A screen protecting the dewatering intake; 2. Energy dissipation at the end of the dewatering hose to slow the water down; 3. Routing the water through vegetation to encourage sediment deposition in the vegetation; 4. Discharging it into a stilling basin; 5. Directing the water through two rock check dams to provide opportunities for additional sediment deposition before the water was discharged into the lake. A floating silt curtain was also installed in Lake Susan. The curtain was installed in a small, accessible part of the lake as insurance against any failure of all the other erosion and sediment control measures. No such failure occurred. A small amount of sediment may have entered the lake as a result of the pond reconstruction project; however, the majority of the delta already existed prior to the project. This is depicted in the attached photo, taken in October 2001 (Attachment 1). The pond reconstruction project is expected to yield a net decrease in the rate of sediment deposition in this area. Todd Gerhardt Lake Susan Erosion October 1, 2003 Page 3 of 3 The Minnesota Department of Natural Resources, Carver SWCD and City of Chanhassen have all inspected the delta and have determined that it is not an imminent threat to the lake system. Aaron Mlynek from the Carver SWCD recently met with one of the residents on Lake Susan and followed up with a letter (Attachment 2). Julie Ekman from the Carver SWCD has been in contact with the same resident. Her follow-up letter is also attached (Attachment 3). TIMELINE Below is the proposed timeline for the stabilization of the northern shoreline of Lake Susan. It also includes meetings with private property owners to discuss options and resources for stabilizing their shorelines. Goal Letter to District requesting funding Neighborhood Meeting #1 (Options) Neighborhood Meeting #2 (Resources) Prepare Plans and Specifications Advertise for Bids Award Bid Construction Projected Date October 2003 Winter 2003 Winter/Spring 2004 Spring 2004 Summer 2004 Late Summer 2004 Late Fall/Winter 2004 ATTACHMENTS 1. Photo of Sediment Delta, taken October 3, 2001 2. September 26, 2003 Letter from Carver SWCD to Kenneth Wencl 3. October 2, 2003 Letter from DNR to Kenneth Wencl CARVER CONSERVATION OlSTRKT 1946 219 East Frontage Road Waconia, MN 55387 Phone: 952-442-5101 Fax: 952-442-5497 http://www.co, carver, mn. us/SWCD/SWCD main. html Mission Statement: To provide leadership in conservation and teach stewardship of the soil, water, and related resources through a balanced, cooperative l~'ogram that protects, restores, and improves those resources. September 26, 2003 Kenneth Wencl 8412 Great Plains Blvd Chanhassen, MN 55317 Re: Lake Susan / Regional Pond Sedimentation Concerns CITY OF CHANHASSEN Mr. Wencl: This letter is a summary and response to your erosion and sedimentation concerns regarding Lake Susan and the recent Lake Susan Regional Pond project. The following comments are related to our knowledge of the project, conversations with the DNR and City of Chanhassen and correspondence w~ v~m~' self which includes the meeting between you and me on September 25, 2003. We take c~tizen' s input and concerns seriously. We conduct field investigations on all inquiries and make professional decisions based on as much significant data that is aq, ailable to us. When data is not complete, as is in most cases of water and natural resource concerns, we must rely on the best information available and our professional judgment. Regi.0__nal_po_.nd Project Thc ~eg~onal pond project, which was recently completed, included dewatering the basin during excavanon and grading operations to enhance the water quality treatment of storm water prior to entering Lake Susan. The SWCD was involved in preliminary planning of the erosion and sediment controls and dewatering practices of the project. A meeting was held April 17th, 2003 to discuss the project with the parties involved. Subsequent monitoring of the dewatermg practices and erosion and sediment controls took place on May 22, June 10, June 27, July 8, July 16, July 30, August 14, August 28, and September 9, 2003. The project began dewatering the basin in mid-May was done dewatering in early July 2003. During the monitoring activities the SWCD did not witness sediment- laden water discharging fi.om the dewatering activities. Lake Susan and Riley Creek Lake Susan has a 1,198-acre watershed [consisting of 559 acres low denfity residential, 67 acres medimn density residential, parks and 547 open areas, and 25 acres commercial land use]. The lake has a surface area of 81 acres, a maximum depth of 16 feet, and a mean depth of 10 feet. Its approximate volume is 800 acre-feet. The delta of sediment is a common and natural occurrence where streams discharge into larger water bodies. Streams carry various levels of sediment suspended in the water naturally. When the streams discharge to a water body, the velocity of the water slows, allowing deposition of sediment in the water body. AN EQUAL OPPORTUNITY EN[PLOYER The amount of sediment deposited into Lake Susan by Riley Creek has been accelerated above natural amounts of sediment due to decades of urban development; land use change, agricultural runoff, sand and salt activities over winters andother contributing factors. However, it is my professional opinion, based on visual observations that the Lake Susan Regional Pond project did not significantly contribute sediment loads to Lake Susan relative to the delta. Further, it is unlikely the sediment deposited on the footings of your dock were caused by the Lake Susan Regional Pond Project. If three inches of material was deposited on your shoreline from across the lake, intuitively at least 3 inches of material would cover the majority of the lake bottom throughout the lake area. With Lake Susan having a surface area of 80 acres, three inches of sediment over the entire lake would total more than 32,000 cubic yards of material. In other terms, about 2,000 medium-sized dump tracks. Riley Creek Watershed Area A portion of Riley Creek flows out of Lake Ann and flows into Lake Susan; that is a distance of approximately 2 miles. The watershed area in the two miles is approximately 507 acres, which includes a variety of land uses including residential, commercial, industrial, roads, and open space. Within this large watershed, overtime, sediment from the changing land use and road sanding could have contributed to the increase in sediment load to Susan Lake. Further, natural erosion processes would likely contribute to a sediment delta in Lake Susan. at the mouth of Riley Creek at Lake Susan. Under normal conditions, all streams flowing into a lake will produce a delta. Removal of the delta could further expose and suspend soils and sediment; removal of the delta could actually further impact the lake. In addition, the amount of funds needed for the removal of the sediment would outweigh the potential benefits of removal. As in all water quality benefits, prevention is the only practical manner to address improvements. CitiZen Involvement Concerned citizens can be involved in a variety of ways which includes observing and monitoring construction areas and land use changes, reporting sUdden changes in color of lake water and stream water. Citizens can also get involved in participating in a citizen lake monitoring program which includes recording climatological data and conducting water clarity readings for the Pollution Control Agency and lake water levels on a regular basis for the Department of Natural Resources. Information on the citizen lake monitoring programs can be obtained at http ://www.pca` state, mn. us/water/clmp.html and http ://www. dnr. state, mn. us/volunteering/lakelevelmn, html. Citizen involvement in managing their property for the improvement of lakes is very important. If there is interest from shore land property owners and property owners in the watershed of Lake Susan a meeting with residents, city employees, SWCD employees and others could be scheduled to discuss Lake Susan and management activities to help water quality and long-term lake health. Included in this meeting would likely be shoreline restoration practices to reduce shoreline erosion, increase water quality, and promote good lake habitat for fish and wildlife in the littoral zone of the lake. The Carver SWCD is directed by a five-member elected Board and managed by Tim Gieseke. You may locate these contacts on the website (www. co.carver.mn, us/SWCD/SWCD_main, htm) or at 952- 442-5101. S in/ca'-hr ely, ~~e~, CPES C-IT Urban Conservation Technician cc. Lori Haak, City of Chanhassen; Julie Eckman, Area Hydrologist October 2, 2003 Minnesota Department of Natural Resources Central Region Waters - 1200 Warner Road, St. Paul, MN 55106-6793 Telephone: (651) 772-7910 Fax: (651) 772-7977 Kenneth Wencl 8412 Great Plains Blvd. Chanhassen, Minnesota 55317 RE: Lake Susan Dear Mr. Wencl: I received your letter and appreciate your concerns regarding water quality in Lake Susan. I visited Lake Susan on Monday, September 22, during a tour of the Riley-Purgatory-Bluff Creek watershed. This delta is a repository for sediment carried in by Riley Creek from the watershed. The maintenance work done recently at the sediment pond is one factor of many that contribute to the sediment load carried by the creek. Therefore, I am unable to differentiate between the amount of sediment that is from the watershed as a whole and that contributed by the recent maintenance project. Development that has occurred over the years in the watershed area upstream from Lake Susan contributes to more sediment loading in the creek and an acceleration of build-up at the delta over what would occur naturally. In addition to sediment transport at the inlet, erosion and sediment build-up in Lake Susan is impacted by shoreland practices around the lake. Where shoreline aquatic vegetation is removed or absent, wave action is no longer attenuated and shoreline erosion occurs at an accelerated rate. Lawn areas provide negligible protection from the force of rain hitting the ground and consequently soil particles are loosened and transported with runoff. The absence of natural vegetation between the shoreline and the lawn area allows this sediment to be transported into the lake. Additionally, typical lawn grasses have very short root systems (2"-3") that do little to stabilize the soil; consequently, slumping with subsequent erosion and sediment transport frequently occurs in areas of steeper slopes. Along the shoreline and in the lake, shade is important for aquatic life; placement ofriprap with the removal of vegetation that provided shading and refuge also contributes to the process of lake degradation. All of these factors impact the sediment build- up in a lake. The water level in Lake Susan has receded, due to the lack of rain, revealing more of the delta area. If you and other residents are concerned about the rate of sediment build-up at the delta, you can approach the Riley-Purgatory-Bluff Creek Watershed District or the City of Chanhassen and ask that they consider removal of the sediment. Keep in mind, however, that the act of sediment removal can also cause detrimental impacts to the lake by stirring up sediments and the nutrients that they contain. For long-term improvement to water quality in Lake Susan, perhaps lakeshore residents would consider applying some of the shoreline restoration techniques described in the enclosed pamphlet. If lakeshore residents took steps to reduce erosion on their own property by returning the shore area to more natural conditions, significant improvement in Lake Susan's water quality could be realized over time. Contact me at the phone number above if you would like more information on how to proceed with shoreline restoration projects. ~~cerely, Area Hydrologist Enclosure C: City of Chanhassen, Lori Haak ~r Carver SWCD Urban Conservation Technician, Aaron Mlynek Riley-Purgatory-Bluff Creek WSD, Bob Obermeyer DNR Information: 651-296-6157 · 1-888-646-6367 · TrY: 651-296-5484 · 1-800-657-3929 An Equal Opportunity Employer ~ Printed on Recycled Paper Containing a Who Values Diversity ~ll~[[ Minimum of 20% Post-Consumer Waste