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Home My WebLink About609 S COLLEGE AVE MIXED USE - BDR200004 - SUBMITTAL DOCUMENTS - ROUND 2 - STORMWATER-RELATED DOCUMENTS (2)July 1, 2020 LOMA REPORT 609 South College Avenue Fort Collins, Colorado Prepared for: South College 609 LLC 262 East Mountain Avenue Fort Collins, CO 80524 Prepared by: 301 N. Howes Street Suite 100 Fort Collins, Colorado 80521 Phone: 970.221.4158 www.northernengineering.com Project Number: 564-005 This Drainage Report is consciously provided as a PDF. Please consider the environment before printing this document in its entirety. When a hard copy is absolutely necessary, we recommend double-sided printing. July 1, 2020 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: LOMA Report for 609 South College Avenue Dear Staff: Northern Engineering is pleased to submit this LOMA Report for your review. This report accompanies the development submittal for the proposed 609 South College Avenue project. If you should have any questions as you review this report, please feel free to contact us at your earliest convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Aaron Cvar, PhD, PE Senior Project Engineer 609 South College Avenue TABLE OF CONTENTS Page I. PROJECT DESCRIPTION AND BACKGROUND .................................................................................... 1 II. STUDY LIMITS AND MAPPING .......................................................................................................... 4 III. HYDROLOGY AND HYDRAULICS ....................................................................................................... 5 IV. DISCUSSION OF RESULTS ................................................................................................................. 6 V. REGULATION COMPLIANCE ............................................................................................................. 6 References .................................................................................................................................................... 7 LIST OF FIGURES Figure 1-Vicinity Map…………………………………………………………………..……………………………………………….…………1 Figure 2-Aerial Photograph………………………………………………………………………………………………………….……...... 2 Figure 3-Current Effective Floodplain Mapping…..…………………………………………………………..………………………4 Figure 4-Project Control Point/Benchmark Information.……………………………………………..……………….…………5 APPENDICES APPENDIX A.1 – LOMA Exhibit – Existing Conditions APPENDIX B.1 – City Floodplain Mapping APPENDIX B.2 – Fort Collins Flood Risk Maps APPENDIX C.1 – Correspondence 609 South College Avenue LOMA Report Page | 1 I. PROJECT DESCRIPTION A. Purpose 1. The purpose of this LOMA report is to summarize floodplain information pertaining to the above referenced project site, and to verify that portions of the property previously identified within a City of Fort Collins defined 100-year flood zone are in fact elevated above Base (100-year) Flood Elevation (BFE). B. Site Location 1. Vicinity Map Figure 1 – Vicinity Map 2. The project site is located in the northeast quarter of Section 14, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 3. The project site is located just southwest of the intersection of Myrtle Street and College Avenue. 609 South College Avenue LOMA Report Page | 2 4. As this is an infill site, much of the area surrounding the site is fully developed. C. Description of Property 1. The development area is roughly 0.2 net acres. Figure 2 – Aerial Photograph 2. The subject property is currently composed an existing residential structure, and landscaped areas. Existing ground slopes are relatively flat (i.e., 0 - 1±%) through the interior of the property. General topography slopes from west to east, towards S. College Avenue. 3. There are no major drainageways within or adjacent to the project site. 4. The proposed project site plan is composed of the development of a building extension, alleyway parking, and site landscaping. Associated utility work and required site work, such as the addition of minor stormwater water treatment facilities will be involved with the development project. SITE 609 South College Avenue LOMA Report Page | 3 D. Project Participants 1. The project is being conducted by a private developer, South College 609 LLC. E. Special Considerations 1. There are no special considerations for the proposed project. II. BACKGROUND A. Flooding Source and History 1. The subject property is not located in a FEMA regulatory floodplain. The project site is, however, located partially within the City of Fort Collins regulated West Myrtle Street floodplain, which is part of a larger basin study, the Old Town Basin. 2. The source of flooding for this area is a portion of the Old Town Basin, as identified by the City of Fort Collins Stormwater Utility. The Old Town Basin has an overall drainage area of roughly 2120 acres, and receives some runoff from the Canal Importation Basin located directly west of the Old Town Basin. The majority of runoff from the Old Town Basin is directed into the Cache La Poudre River. The basin experiences frequent flooding, and the City of Fort Collins is currently underway with a master plan update, with the goal of addressing stormwater quality and identifying stream restoration projects that protect the City’s watersheds. 3. The question of inadvertent detention has been discussed, and initially, it was thought that compensatory storage may be necessary with any fill placed within the development site. However, per email dated January 2, 2020, this area is not within the inadvertent detention ponding area, which was referred to as the “College and Mulberry Pond”. 4. Based on recent updated 2D modeling, the Base Flood Elevation (BFE) for this site is 4995.50 (NAVD 88). Again, this information is based on correspondence with the City of Fort Collins Stormwater Utility. Please see email dated January 2, 2020, provided in Appendix C.1. 5. Please see Figure 3, below for current City of Fort Collins flood mapping of the area. A larger scale view of City floodplain mapping is provided in Appendix B.1. B. Purpose of Study and Background 1. The project proposes to add an addition to the rear (west side) of the existing building adding approximately 800 sf. Construction activities will also include the removal of the existing garage. A concrete patio area, concrete walks, and alley parking will also be added as a part of these improvements, as well as a rain garden similar to what was used at the Music District to provide LID treatment to the site. A dedicated fire service and a single-phase transformer will also be added as part of this project. 2. The purpose of this study is to document existing site conditions which warrant a Letter of Map Amendment (LOMA). 609 South College Avenue LOMA Report Page | 4 Figure 3 – Current City of Fort Collins Floodplain Mapping (Source: FCMaps, http://gisweb.fcgov.com) III. STUDY LIMITS AND MAPPING A. Study Limits, Mapping 1. The project site is located just southwest of the intersection of South College Avenue and Myrtle Street. There is a backwater area beginning just northeast of the project site, and this project is located within this backwater area. 2. Existing site elevations are based on field surveyed topography. Field survey of the site is referenced to the NAVD 88 datum; however, many surrounding sites have been designed utilizing the NGVD 29 datum. 3. It is noted that all contours and elevations shown on the LOMA exhibits provided in this report, as well as all design drawings associated with the project are referenced to the NAVD 88 datum. The conversion factor from NAVD 88 to NGVD 29 is negative 3.18-feet. SITE 609 South College Avenue LOMA Report Page | 5 4. Control points utilized with the survey completed for the project are as per the plan set for the project as shown in Figure 4: Figure 4 – Project Control Points/Benchmark Information (Source: Utility Plans for 609 South College Avenue, Northern Engineering) IV. HYDROLOGY AND HYDRAULICS A. Hydrology, Hydraulics 1. The project site is located just southwest of the intersection of South College Avenue and Myrtle Street. The proposed fill is not within a conveyance zone, rather it is located within a backwater area. As discussed above, and based on correspondence with City Staff, the project is not located within an inadvertent detention area; therefore, compensatory storage is not a requirement for the site. 2. Since the project site is not located within an active conveyance zone, no hydraulic modeling changes are proposed with this project. 609 South College Avenue LOMA Report Page | 6 V. DISCUSSION OF RESULTS A. Mapping Changes 1. No mapping change is proposed with the project, as this is a Letter of Map Amendment (LOMA). This study is only providing better elevation data and comparing this data to existing Base Flood Elevation. 2. A Base Flood Elevation of 4995.50 (NAVD 88) has been provided by the City of Fort Collins, as discussed above. 3. Utilizing this existing BFE, we have prepared a Metes and Bounds Description, in which all areas of the property outside of the metes and bounds area are naturally elevated above flood elevation before the placement of any fill on the site. 4. The proposed project will not place any structure outside of the metes and bounds area, as this area may be subject to flooding in the 100-year storm event. VI. REGULATION COMPLIANCE A. Compliance with Standards 1. Floodplain design proposed with the 609 South College Avenue project complies with the City of Fort Collins Old Town Master Drainage Plan (Ref. 1). 2. There are no FEMA regulatory floodplains associated with the 609 South College Avenue development. However, the project is impacted by the Old Town Basin Floodplain, which is a City regulated floodplain. Areas of the project site, as defined by Metes and Bounds Description (by separate document) will be removed from flood zone status by the current LOMA. For areas of the property outside of the metes and bounds area, all provisions within Chapter 10 of the City Municipal Code shall be adhered to. 609 South College Avenue LOMA Report Page | 7 References 1. Old Town Basin Master Drainage Plan, Anderson Consulting Engineers, May 2002. 2. Drainage Memo for 609 South College Avenue, July 1, 2020, Northern Engineering. (Currently Under Review) APPENDIX A.1 LOMA Exhibit – Existing Conditions C.O. G W C S E VAULT ELEC TELE T VAULT ELEC VAULT ELEC / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / E E E X E E E W B 605 COLLEGE LTD 605 S COLLEGE AVE FORT COLLINS, CO 805243003 GATON III INC DBA CANINOS ITALIAN RESTAURANT 613 S COLLEGE AVE FORT COLLINS, CO 805243003 SOUTH COLLEGE AVENUE DALZELL ALLEY EXISTING 100-YR FLOODPLAIN (CITY OF FORT COLLINS) BASE(100-YR) FLOOD ELEVATION =4995.50 (NAVD 88) EXISTING BUILDING FFE = ±4997.3 (NAVD 88) LOMA BASIS: EXISTING GROUND CONTOUR PER FIELD SURVEY=4995.50 (NAVD 88) PROPOSED LOMA METES & BOUNDS LINE LOMA EXHIBIT - EXISTING CONDITIONS FORT COLLINS, CO 609 S. COLLEGE E NGINEER ING N O R T H E RN JULY 1, 2020 P:\564-005\DWG\DRNG\564-005_LOMA.DWG ( IN FEET ) 0 1 INCH = 20 FEET 20 20 APPENDIX B.1 City Floodplain Mapping &KZdK>>/E^'/^DWW/E'—&DW^ ŚƩƉƐ͗ͬͬŐŝƐǁĞď͘ĨĐŐŽǀ͘ĐŽŵͬ APPENDIX B.2 Fort Collins Flood Risk Maps S COLLEGE AVE DALZELL ALY W MYRTLE ST CORBIN ALY E MYRTLE ST . Printed: 10/30/2019 All are floodplain approximate. boundaries This Agency information (FEMA) Flood is based Insurance on the Federal Rate Map Emergency (FIRM) and Management the City of Fort that the Collins referenced Master Drainageway property will or Plans. will not This be free letter from does flooding not imply or damage. City Designated A property Floodplain not in the may Special be damaged Flood Hazard by a flood Area greater or in a than not shown that predicted on the map. on the This map map or from does a not local create drainage liability problem on the part that results of the City, from or reliance any officer on this or employee information. thereof, for any damage City Flood Risk Map Moderate Risk May - Areas include: of FEMA 500-year floodplain (FEMA Zone X-shaded). - average Areas of depths FEMA or of City less 100-than year 1 foot. floodplain (sheet flow) with Low Risk - Areas protected by levees from the 100-year flood. Areas floodplains. outside Local of FEMA drainage and problems City mapped may 100-still year exist. and 500-year City - Areas Flood of FEMA Fringe 100-- May year Include:floodplain (FEMA Zones A, AE, AO, and AH) - flow Areas areas of City with 100-average year floodplain depths of including 1-3 feet. ponding areas and sheet There is a 1% annual chance that these areas will be flooded. High Risk City fastest Floodway velocities. - Area of 100-year floodplain with greatest depths and 0 15 30 60 90 120 Feet 609 S COLLEGE AVE XS#:1205 4990.5ft NGVD 29 XS#:1364 4990ft NGVD 29 XS#:1699 4992.8ft NGVD 29 XS#:1529 4992.5ft NGVD 29 XS#:1882 4993.7ft NGVD 29 XS#:1929 4992.3ft NGVD 29 S COLLEGE AVE W MYRTLE ST DALZELL ALY E MYRTLE ST CORBIN ALY . Printed: 11/07/2019 All floodplain boundaries are approximate. This information is based on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) and the City of Fort Collins Master Drainageway Plans. This letter does not imply that the referenced property will or will not be free from flooding or damage. A property not in the Special Flood Hazard Area or in a City Designated Floodplain may be damaged by a flood greater than that predicted on the map or from a local drainage problem not shown on the map. This map does not create liability on the part of the City, or any officer or employee thereof, for any damage that results from reliance on this information. City Flood Risk Map Moderate Risk May include: - Areas of FEMA 500-year floodplain (FEMA Zone X-shaded). - Areas of FEMA or City 100-year floodplain (sheet flow) with average depths of less than 1 foot. - Areas protected by levees from the 100-year flood. Low Risk Areas outside of FEMA and City mapped 100-year and 500-year floodplains. Local drainage problems may still exist. City Flood Fringe - May Include: - Areas of FEMA 100-year floodplain (FEMA Zones A, AE, AO, and AH) - Areas of City 100-year floodplain including ponding areas and sheet flow areas with average depths of 1-3 feet. There is a 1% annual chance that these areas will be flooded. High Risk City Floodway - Area of 100-year floodplain with greatest depths and fastest velocities. 0 20 40 80 120 160 Feet APPENDIX C.1 Correspondence 1 Aaron Cvar From: Daniel Evans <daevans@fcgov.com> Sent: Thursday, November 7, 2019 2:50 PM To: Nick Haws Cc: Aaron Cvar Subject: RE: 609 S. College Ave. | Old Town Stormwater Master Plan Hydrology Update Attachments: College&Myrtle Floodplain.pdf; College&Mulberry Pond.pdf Nick, There are couple things going on here: 1) There is the existing regulatory floodplain (see attached Flood Risk Map). 2) There is the College and Mulberry Pond what is part of ICON’s 2016 Hydrology Update for Old Town (see attached figure for College&Mulberry Pond). The 100-year elevation of the pond is around 4996.5. I also have Icon’s Hydrology Report that we can go through and I can make you copies of anything you’d like from that. I’m available on the 15th in the morning until 11am. Dan From: Nick Haws <nick@northernengineering.com> Sent: Thursday, November 7, 2019 10:53 AM To: Daniel Evans <daevans@fcgov.com> Cc: Aaron Cvar <aaron@northernengineering.com> Subject: 609 S. College Ave. | Old Town Stormwater Master Plan Hydrology Update Dan, Can you please send over the mapping for the City Recognized Inadvertent Stormwater Storage Area (aka, “College and Mulberry storage pond”)? Of particular interest is the area southwest of College and Myrtle. Any additional detail relative to depth and volume of storage on the 609 S. College Ave. property would be extremely helpful as well. Assuming you are able to get this information to us by the first part of next week, I would like to schedule an in- person meeting with you to follow-up on November 15th. Please let me know if there are times that work for you that Friday. Thanks, Nick Haws, PE, LEED AP President, CEO 301 N. Howes Street, Suite 100 | Fort Collins, CO 80521 820 8th Street | Greeley, CO 80631 D: 970.568.5414 O: 970.221.4158 M: 970.690.0927 www.northernengineering.com S MASON ST W MYRTLE ST S COLLEGE AVE E MYRTLE ST 100-year Pond Elevation 4996.5 College and Mulberry Pond 1 Aaron Cvar From: Heidi Hansen <hhansen@fcgov.com> Sent: Friday, January 3, 2020 3:48 PM To: Aaron Cvar Cc: Daniel Evans; Claudia Quezada; Shane Boyle Subject: Music District Hi Aaron, For the Music District project at 609 S College:  The 2D modeling shows that this property should not be within the inadvertent detention ponding area so you will not need to balance cut/fill on the site to account for the detention volume  For the floodplain use permit please use the effective BFE of 4995.5’ NAVD88, so the Regulatory Flood Protection Elevation (RFPE) for an Addition RFPE=BFE+12” = 4996.5’. It sounds like much of the ground is higher than that so it should make “elevating” the structure easy. Please remember that no basements are allowed in the regulatory floodplain. A metes and bounds LOMA may be an option if the existing ground where the addition will be is all high, but we still would strongly discourage a basement due to the known flood risk in the area. If you have any additional questions please let me or Claudia know. Thanks, Heidi Heidi Hansen, PE, CFM Engineer III – Floodplain Management ASFPM Chapter Director – District 4 City of Fort Collins - Utilities 700 Wood St. Fort Collins, CO 80521 970.221.6854 (desk)