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Home My WebLink About7/28/2021 Item 4a, Schroeter (2) Wilbanks, Megan From:Schroeter Family < To:E-mail Council Website Subject:Fwd: Planning Commission Hearing - Comments on Item 4a Attachments:2E021040701_Schroeter Comment to 500 Westmont Meinhold Property Housing Development Storm Flow and Flooding Risk.pdf This message is from an External Source. Use caution when deciding to open attachments, click links, or respond. Confirming this letter below was received as I did not see it posted on the Planning Commission agenda correspondence. Thank you. ---------- Forwarded message --------- From: Schroeter Family < Date: Wed, Jul 28, 2021 at 12:44 PM Subject: Planning Commission Hearing - Comments on Item 4a To: Van Leeuwen, Kyle <KVanLeeu@slocity.org>, < Cc: < , Schroeter Family < Attached are comments for Agenda Item 4A: 468/500 WESTMONT AVE (SBDV-0169-2020, EID-0170-2020) REVIEW OF TTM NO. 3157, 23 LOT SUBDIVISION AND ENVIRONMENTAL REVIEW I would also like to share a video, but the file appears to be too large. Do you have an FTP site for uploading? Thank you, Robert Schroeter, PhD 1 Mr. Kyle Van Leeuwen July 28, 2021 Page 1 July 28, 2021 Mr. Kyle Van Leeuwen Associate Planner City of San Luis Obispo 919 Palm Street San Luis Obispo, CA 93401 kvanleeuwen@slocity.org PUBLIC COMMENTS REGARDING FLOOD FLOWS - REVIEW OF A TENTATIVE TRACT MAP (TRACT 3157) TO CREATE 23 RESIDENTIAL LOTS ON AN EXISTING 4.98-ACRE SITE WITHIN THE LOW-DENSITY RESIDENTIAL (R-1) ZONE AND MITIGATED NEGATIVE DECLARATION FOR 468-500 WESTMONT AVENUE TENTATIVE TRACT MAP – DATED APRIL 2021 (STATE CLEARINGHOUSE NUMBER: 2021040701) Dear Planning Commissioners: The proposed 468-500 Westmont Project, through the addition of 23 homes with possible ADUs and JADUs on a small 5-acre parcel with a creek, will alter groundwater recharge and groundwater flow and more importantly surface water flow to the creek. Many homes in the surrounding neighborhoods of the Project have existing stormwater problems, including standing water under their homes and yard and street flooding. This is due, in part, to poor soil drainage in the local area and the already high flow in the mainstem of West Fork Twin Ridges Creek during storm events. Twin Ridges Creek does not have the capacity to take on more flood flows, especially given increasing vegetation and debris accumulation in the stream channel. See attached photos and video. The Project includes a “Drainage Report”, however it is not clear if the report includes the severe local flooding conditions in the pre-project conditions. Furthermore, the report does not describe how the existing flood conditions may be affected or exacerbated by the Project and does not provide any information describing how the Project may increase flood risk and property damage to the residents along the creek. The two pictures show street flooding along Clover Drive during a particularly large storm event in 2017. The back up in stormwater occurred largely due to there being nowhere else for the water to go, since the flow in Twin Ridges Creek was already at flood stage. Mr. Kyle Van Leeuwen July 28, 2021 Page 2 The following image below, taken from a video in January 2017, shows West Fork Twin Ridge Creek at very high flow at the culvert (marked by the arrow) that passes under Westmont Drive and is situated just upstream of the Project and the confluence of East Fork Twin Ridges Creek. The video is also included as an attachment to this comment letter. The Project design currently plans to have stormwater diverted from impervious surfaces including homes, driveways and streets to flow into stormwater basins that will then enter back into East Fork Twin Ridges Creek before the confluence with West Fork Twin Ridges Creek. Any increased discharge from the Project will ultimately affect flow in West Fork Twin Ridges Creek. Given the significant increase in impervious surfaces in the Project, much of the water that once had an opportunity to infiltrate into the soils and become groundwater will be lost from the system. Changes in infiltration and flow are likely to impact the hydrology of the small and sensitive rip arian found Mr. Kyle Van Leeuwen July 28, 2021 Page 3 along East Fork Twin Ridges Creek. Keep in mind that at a minimum, 23 roofs will be diverting rainwater away from the soil where absorption could have occurred. If each lot also has ADUs and JADUs, that would be an additional 46 rooftops and even less ground exposure for natural infiltration of rainwater into the surrounding soils. Any further disturbance to this system could intensify these flood flows with dangerous consequences, especially with more frequent and intense storms expected as a result of climate change. Thank you for the opportunity to comment on the Initial Study. If you have any questions regarding this letter, please contact me via email at schroeters617@gmail.com. Sincerely, Robert Schroeter 617 Jeffrey Drive, San Luis Obispo, CA 93405 cc: (via email) Governor’s Office of Planning and Research State Clearinghouse State.Clearinghouse@opr.ca.gov