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AGENDA RECOMMENDATION |
Consent Calendar 5.H.
City Council Regular Meeting
- Meeting Date:
- 12/09/2024
Agenda Item:
Resolution approving a Conditional Use Permit to allow for cut, fill and development activities on a slope equal to or in excess of seventeen-point six (17.6) percent for ravine stabilization. The subject property is described as Lot 5, Block 1, Ironwood Oaks subdivision (80 Telemark Drive); by request of Andrew Manske.
Recommendation/Action(s):
At the November 20, 2024, meeting, the Planning Commission recommended the adoption of the resolution approving the conditional use permit.
Summary:
The property owner, Andrew Manske, is requesting a conditional use permit to allow for cut, fill and development activities on a slope equal to or in excess of seventeen-point six (17.6) percent for ravine stabilization. The subject property is located at 80 Telemark Drive and is legally described as Lot 5, Block 1, Ironwood Oaks subdivision.
Mankato City Code section 10.82 Subd. 10, Environmentally Sensitive Areas, Slopes, states that, "All cut, fill, and development activities on a slope equal to or in excess of seventeen-point six (17.6) percent may be permitted only as a conditional use. In addition to the submittal requirements for a conditional use permit application, a plan shall be submitted at a scale required in Section 10.90, Subdivision 6, and the plan shall include two (2) foot topographic contour intervals depicting existing and proposed topography. The plan shall be signed by a registered surveyor or engineer in the State of Minnesota."
The existing residential house located at 80 Telemark Drive has a bluff/ravine area in the rear yard. In July 2024, due to excess rain events, slope failures occurred in the bluff/ravine area of the subject property. According to the engineering report provided, the area had seen excessive rain (10+ inches of rain) prior to the slope failure. The house and property, including a pool area, driveway, and sport court are located at the top of a ravine that extends down approximately 40 feet in elevation to the southwest to a flat area. The slope failure extends adjacent to the property down into the ravine to the southwest.
According to the preliminary engineering report, based on the topographic map, prior to slope failure, the ravine slope had an inclination of approximately 30 to 40 degrees. A creek exists to the southwest of the property at the bottom of ravine area. Per the topographic map, the creek channel is approximately 100 feet southwest from the toe of the ravine slope adjacent to the house. The creek channel is incised approximately 8 to 10 feet. Maps also show a peninsula/ bluff extending to the south of the house before dropping off into the ravine area.
The applicant has obtained preliminary engineering outlining options for ravine stabilization in the area. The options provided in the report are:
The Braun engineering report states that for any of the slope repair options, the recommendation is that the homeowner review water runoff from the property down the ravine slope to reduce the potential for excessive runoff over and down these over steepened slopes. If drainpipes are used, the pipes should extend to at least the toe of the ravine slope to reduce water runoff onto the slope. A recommended condition is included herein that addresses this engineering recommendation.
The Braun engineering report goes on to state that for each of the slope repair options, access may be difficult for construction equipment. A recommended condition is included that with the submission of the construction plans, a construction staging plan is provided that demonstrates how the construction equipment will access the site and how any potential material storage will be handled for the project. A recommended condition is also included that once the final scope of work is developed and the repair method established, a minimum of 10 days prior to work beginning, the applicant conducts an informal meeting with the neighbors to inform them that the project will be occurring. Staff will provide the applicant with the list of names and addresses that were used for the required conditional use for assisting with this condition.
The provided Braun report states, "additionally, the yard, pool and sport court will likely be affected by slope repair construction activities." A recommended condition is included herein that states that upon the completion of a project, all attempts shall be made to reestablish the minimum 10' bluff setbacks for code compliance for the sport court which was recently constructed. The pool is in an existing condition that was constructed in 2014 prior to the current property ownership. The recommendation related to the pool area is that all reasonable attempts shall be made to reestablish the previously approved pool setback location on the bluff. Ideally, the project will reestablish all minimum setbacks. However, if a licensed engineer determines that it is not feasible for the noted setbacks to be reestablished, the City's engineer department will analyze the engineering documentation for reasonableness and approval.
The Braun report refers to property boundaries. The information that has been provided indicates that all work will be contained wholly upon the subject property. A recommended condition is included that prior to any work occurring, the official property boundary be established to ensure that there are no encroachments onto adjacent properties. If, through the preparation of the engineered construction plans, encroachments are recommended, the property owner will be required to work with the adjacent property owner(s) and secure appropriate permissions for any desired encroachment prior to work occurring and being permitted.
The subject property is included within the plat of Ironwood Oaks, which was approved in 1984 while the property was located in Mankato Township. The plat identifies a 20' drainage easement on the southern boundary of the subject parcel. A recommended condition is included herein that the referenced drainage easement be maintained and that further changes or modifications to the existing 20' drainage way and easement area are prohibited.
A site visit was conducted with staff, the applicant and the applicant's construction professional on October 14, 2024. At the time of the inspection, the bluff was noted to be stable, and additional failure was not actively occurring. In the event the stability of the bluff changes prior to the final approval, or the building permit being issued, a recommended condition is included herein that recommends that emergency repairs, including tree removal prior to official preparation and approval of the construction plans, will require evaluation by an engineer hired by the applicant, the city's designated engineer and the owner or owner's representative.
In addition to the bluffs on the site, the subject property contains areas identified as, "Environmentally Sensitive Areas, Woodlands" in Mankato City Code section 10.82 Subd. 12. Several of the existing trees located in the slope failure area were damaged when the slope failure occurred, and additional trees may need to be removed when the engineered plans are prepared for complete correction. Mankato City Code provides that removal of trees or other vegetation from woodlands where such action is necessary to protect public health, protect property from damage or to restore public order is an activity that is not subject to further limitation of the woodland section of the Code. As noted above, modifications to the property are necessary to protect the property from additional damage and to restore conformity on the subject site. A recommended condition is included herein that, in conjunction with the project, the applicant shall work with the City Forester to evaluate reasonable options for replanting trees and natural wooded vegetation where determined reasonable and feasible, and the applicant will be required to provide a landscaping plan incorporating the subject plantings and the plantings shall be installed in conjunction with the project. The landscaping plan shall incorporate restoration of the natural, wooded ravine to the greatest extent feasible, based on the final, approved engineering solution.
Mankato City Code section 10.82 Subd. 10, Environmentally Sensitive Areas, Slopes, states that, "All cut, fill, and development activities on a slope equal to or in excess of seventeen-point six (17.6) percent may be permitted only as a conditional use. In addition to the submittal requirements for a conditional use permit application, a plan shall be submitted at a scale required in Section 10.90, Subdivision 6, and the plan shall include two (2) foot topographic contour intervals depicting existing and proposed topography. The plan shall be signed by a registered surveyor or engineer in the State of Minnesota."
The existing residential house located at 80 Telemark Drive has a bluff/ravine area in the rear yard. In July 2024, due to excess rain events, slope failures occurred in the bluff/ravine area of the subject property. According to the engineering report provided, the area had seen excessive rain (10+ inches of rain) prior to the slope failure. The house and property, including a pool area, driveway, and sport court are located at the top of a ravine that extends down approximately 40 feet in elevation to the southwest to a flat area. The slope failure extends adjacent to the property down into the ravine to the southwest.
According to the preliminary engineering report, based on the topographic map, prior to slope failure, the ravine slope had an inclination of approximately 30 to 40 degrees. A creek exists to the southwest of the property at the bottom of ravine area. Per the topographic map, the creek channel is approximately 100 feet southwest from the toe of the ravine slope adjacent to the house. The creek channel is incised approximately 8 to 10 feet. Maps also show a peninsula/ bluff extending to the south of the house before dropping off into the ravine area.
The applicant has obtained preliminary engineering outlining options for ravine stabilization in the area. The options provided in the report are:
- Regrade the slope to an inclination suitable for the soils present at the site. Preliminarily, based on the soils observed, a stable inclination could be approximately 20 to 30 degrees (approximately 3H:1V to 2H:1V). This option would likely require clearing of most of the trees. Regraded slope extents may be controlled by property boundaries and permits required for construction and may require removal of the sport court and pool areas. Regraded soils should be keyed into the toe of the slope to reduce the potential for sliding.
- A pattern of grouted soil nail anchors and a high-strength wire mesh (Teccomesh or similar product) facing is installed on the slope. For this option, some slope clearing will be required, but large trees could potentially stay in place. This option allows for the site to freely drain and will allow for plant growth through the wire mesh on the slope. A fabric can also be installed below the wire mesh to control the fine-grained soils and allow for seeding and plant growth as well. A shotcrete facing could also be used instead of the wire mesh system. If shotcrete is used, additional clearing and drainage will be required.
- A soldier pile and lagging wall with tieback anchors installed along the top of the slope adjacent to the yard, pool and sport court. Soldier piles would generally be installed to a depth below the creek bottom elevation to reduce the potential for undercutting and to provide lateral support. Tieback anchors would be installed in rows near the top of the wall to stabilize the soils in the upper slope and provide support for the yard, pool and sport court. The soil below the wall could be left in place but would be subject to future erosion.
The Braun engineering report states that for any of the slope repair options, the recommendation is that the homeowner review water runoff from the property down the ravine slope to reduce the potential for excessive runoff over and down these over steepened slopes. If drainpipes are used, the pipes should extend to at least the toe of the ravine slope to reduce water runoff onto the slope. A recommended condition is included herein that addresses this engineering recommendation.
The Braun engineering report goes on to state that for each of the slope repair options, access may be difficult for construction equipment. A recommended condition is included that with the submission of the construction plans, a construction staging plan is provided that demonstrates how the construction equipment will access the site and how any potential material storage will be handled for the project. A recommended condition is also included that once the final scope of work is developed and the repair method established, a minimum of 10 days prior to work beginning, the applicant conducts an informal meeting with the neighbors to inform them that the project will be occurring. Staff will provide the applicant with the list of names and addresses that were used for the required conditional use for assisting with this condition.
The provided Braun report states, "additionally, the yard, pool and sport court will likely be affected by slope repair construction activities." A recommended condition is included herein that states that upon the completion of a project, all attempts shall be made to reestablish the minimum 10' bluff setbacks for code compliance for the sport court which was recently constructed. The pool is in an existing condition that was constructed in 2014 prior to the current property ownership. The recommendation related to the pool area is that all reasonable attempts shall be made to reestablish the previously approved pool setback location on the bluff. Ideally, the project will reestablish all minimum setbacks. However, if a licensed engineer determines that it is not feasible for the noted setbacks to be reestablished, the City's engineer department will analyze the engineering documentation for reasonableness and approval.
The Braun report refers to property boundaries. The information that has been provided indicates that all work will be contained wholly upon the subject property. A recommended condition is included that prior to any work occurring, the official property boundary be established to ensure that there are no encroachments onto adjacent properties. If, through the preparation of the engineered construction plans, encroachments are recommended, the property owner will be required to work with the adjacent property owner(s) and secure appropriate permissions for any desired encroachment prior to work occurring and being permitted.
The subject property is included within the plat of Ironwood Oaks, which was approved in 1984 while the property was located in Mankato Township. The plat identifies a 20' drainage easement on the southern boundary of the subject parcel. A recommended condition is included herein that the referenced drainage easement be maintained and that further changes or modifications to the existing 20' drainage way and easement area are prohibited.
A site visit was conducted with staff, the applicant and the applicant's construction professional on October 14, 2024. At the time of the inspection, the bluff was noted to be stable, and additional failure was not actively occurring. In the event the stability of the bluff changes prior to the final approval, or the building permit being issued, a recommended condition is included herein that recommends that emergency repairs, including tree removal prior to official preparation and approval of the construction plans, will require evaluation by an engineer hired by the applicant, the city's designated engineer and the owner or owner's representative.
In addition to the bluffs on the site, the subject property contains areas identified as, "Environmentally Sensitive Areas, Woodlands" in Mankato City Code section 10.82 Subd. 12. Several of the existing trees located in the slope failure area were damaged when the slope failure occurred, and additional trees may need to be removed when the engineered plans are prepared for complete correction. Mankato City Code provides that removal of trees or other vegetation from woodlands where such action is necessary to protect public health, protect property from damage or to restore public order is an activity that is not subject to further limitation of the woodland section of the Code. As noted above, modifications to the property are necessary to protect the property from additional damage and to restore conformity on the subject site. A recommended condition is included herein that, in conjunction with the project, the applicant shall work with the City Forester to evaluate reasonable options for replanting trees and natural wooded vegetation where determined reasonable and feasible, and the applicant will be required to provide a landscaping plan incorporating the subject plantings and the plantings shall be installed in conjunction with the project. The landscaping plan shall incorporate restoration of the natural, wooded ravine to the greatest extent feasible, based on the final, approved engineering solution.