Loading...
HomeMy WebLinkAbout029.01 Appendix CC.1 - Wetland Review Comment ResponsesMarch 24, 2023 Lynn Hyde, Development Review Planner City of Bozeman 20 East Olive Ave Bozeman, MT 59771 RE: Aaker Subdivision Aquatic Resource Response to Second Review (#22311) Ms. Hyde, In his March 20, 2023 letter to the City of Bozeman, the wetland reviewer, Dr. William Kleindl, PWS, correctly noted that an analysis of impacts to wetland hydroperiod was not included, nor was a monitoring plan with performance criteria included. He also had some concerns regarding the placement of fill for the stormwater retention pond outfalls. The following discussion is intended to address these concerns. Assessment of Potential Changes in Wetland Hydroperiod Wetlands on-site are associated with surface waters, some of which occur within natural drainages that have been degraded over the years from agricultural practices, and others that are wholly or partially supported artificially by irrigation water. The Aaker project proposes to enhance the hydroperiod of the naturally formed wetland, W-01, and adversely impact the hydroperiod of the artificial wetlands found in the central irrigation ditch, Ditch-02/W-02. This will occur by diverting water westward at the south end of Ditch-02 through a pipe and swale to the W-01. Please refer to the attached Figure WL 1.4. Perennial stream flows and flood flows are diverted from Ditch-02 to W-01, thereby increasing the hydroperiod of that drainage and providing additional hydrologic support to the floristically diverse, higher functioning wetland found there. Conversely, wetland W-02 which occurs on either side of the irrigation ditch (Ditch-02), and consists primarily of a narrow band of reed canarygrass, would receive less water. This wetland is currently artificially supported by irrigation water. The future frequency and duration of flows along the ditch are unknown at this time and will be determined by the needs for water by the sole downstream water right holder, the State of Montana at the Montana State Department of Livestock facility located at 1911 West Lincoln Street. It is more likely than not that the vegetation comprising W-02 will be able to persist indefinitely along Ditch-02 under the new hydroperiod. In my opinion, the enhancement of the hydroperiod of W-01 outweighs the change to the hydroperiod to W-02 and that an overall increase in wetland function will result from this modification. Confluence Consulting Inc. Aaker Subdivision Aquatic Resource Response 2 Temporary impacts to hydroperiod may be necessary at other impact locations during construction, but no other permanent impacts to hydroperiod are anticipated. Construction dewatering will be conducted in a manner that minimizes the impacts to hydroperiod to areas outside of the impact zones, as well as minimizes turbidity of the water returned to the wetlands or streams. Monitoring Plan As discussed in the application, all permanently impacted areas will be mitigated at the Upper Missouri Mitigation Bank, and all temporarily disturbed areas will be restored to original elevations and configuration and revegetated with salvaged sod and topsoil, and a native wetland seed mix. It is important to note that the temporary disturbances proposed at these locations will result primarily from vehicular access during construction of the transportation and park infrastructure (e.g., Kagy Boulevard, the pedestrian bridges). As such, the disturbances are anticipated to be topical and not fundamentally change the soils, hydrology, or functioning of these sites. For this reason the proposed monitoring should focus on the success or failure of the revegetation efforts. Please note that this monitoring plan has been added to the Parks Plan per the reviewer’s request. Monitoring of the temporarily disturbed wetland areas will be conducted as follows:  Monitoring will be initiated in late June or July the first new growing season following the impacts.  Monitoring will occur for two years, or until the success criteria has been achieved. Year 1  Two photo points will be established at each impact location, for a total of 16 photo points.  Visual estimates of percent cover at each temporarily impact site will be made by a wetland scientist.  Notes on the wetland hydrology observed during the site visit will be completed.  A brief technical memorandum will be prepared to document the findings, determine whether or not the sites meet the performance criteria, and provide recommendations if they are not. Year 2  Repeat photos will be taken from each of the 14 photopoints established in Year 1.  Visual estimates of percent cover at each temporarily impact site will be made by a wetland scientist.  Notes on the wetland hydrology observed during the site visit will be completed.  Individual wetland sample points will be completed at each temporarily impacted site (9 sample points). Confluence Consulting Inc. Aaker Subdivision Aquatic Resource Response 3  A brief technical memorandum will be prepared to document the findings, determine whether or not the sites meet the performance criteria, and provide recommendations if they are not. Performance Criteria Each temporarily impacted site will be deemed to be successful if it achieves the following performance criteria: 1. The site is determined to be a wetland using current guidance from the U.S. Army Corps of Engineers; and 2. The site is dominated by ≥50% native hydrophytic vegetation. 3. The site contains less than 5% state listed noxious weeds. Stormwater Retention Pond Outfalls The Stormwater Design Report - Appendix U has been updated to reflect the current design. The stormwater retention basins are designed to fully retain storm-runoff from a city prescribed design storm event (i.e., 10 yr, 2 hr, storm). Overflow discharges will be infrequent and occur only during large storm events. None of the retention basin overflow “outfalls” disturb wetlands. The following is excerpted from page 5 of the updated Stormwater Design Report, and I’ve attached the latest stormwater figure to the end of this letter. To accommodate discharge from storm events larger than the design event all retention systems have overflow provisions sized to meet the 25-year peak flow event. The retention basins will contain a significant amount of runoff even from large events, dramatically reducing the actual overflow flow rate and occurrence. To reduce impacts to the adjacent wetland and stream the retention basins in the City Park have a broad rip-rap overflow that allows overflows to disperse into the wetlands adjacent to the stream. The bio-retention basins all include an overflow structure at the downgradient side that conveys the overflow out of the street. The west bioretention overflow (Basin 3) discharges just outside of the wetlands. The east bio-retention overflow (Basin 5) discharges directly to the stream crossing culvert beneath the roadway. Overflows are anticipated to rarely occur, but even so all the basin overflows are situated to minimize impacts to the adjacent wetlands and stream. Confluence Consulting Inc. Aaker Subdivision Aquatic Resource Response 4 Please let me know if you or Dr. Kleindl have any further questions or require additional information. Regards, Richard McEldowney, PWS Sr. Wetland Scientist Enclosures Cc: File, Connor Brown, Cordell Pool OHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEOHEPROFESSIONALENGINEERS &SURVEYORSSTAHLYENGINEERING& ASSOCIATESWEST UNIVERSITY LLC BOZEMAN, MONTANAWL 1.4ENLARGEDIMPACT AREAWEST DRAINAGERETURNAAKER PHASE 1 SUBDIVISION W W W W W WWWWWWWWWWWWWWWWWWWWWWWWWWWWW W W WWWWWWWWWW W SS SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS SS SS SS SSSSSSSSSSSS SS SS SSSSSSSSSSSSSSSSSSUGEUGEUGEUGEUGEUGEUGEUGEUGE UGE UGE UGE UGE UGE UGE UGE UGE UGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGE UGE UGE UGE UGE UGE UGE UGE UGE UGE UGE UGE WWWWWWWWWWWWWWWWWGASGASGASGASGASGASSS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS UGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGEUGCUGCUGCUGCUGCUGCUGCUGCUGCUGCUGC UGCUGCUGCUGEUGEUGEUGEUGEUGEUGE UGEBB B B BBB8'8'8' 1 5-13-22 PHASE 1 PRE-APP CDP ZWL 2 10/11/2022 PRELIMINARY PRICING CDP ZWL 3 10/26/2022 PRELIMINARY PLAT CDP ZWL 4 2/2/2023 PRELIM PLAT RC1 CDP ZWL 5 3/23/2023 PRELIM PLAT RC2 CDP ZWL PROFESSIONALENGINEERS &SURVEYORSSTAHLYENGINEERING& ASSOCIATESAAKER PHASE 1 SUBDIVISION LOCATED IN THE SE 14 OFSECTION 14, T2S, R5EWEST UNIVERSITY, LLCBOZEMAN, MONTANAC5.0PH1 DRAINAGEAND GRADINGPLANNOTES:1.SUBDIVISION STORMWATER RETENTION INCLUDES PHASE 1STREETS.2.ALL LOTS TO HAVE ON-SITE RETENTION.