39 C20-2022-024 Colorado River Protections; District 3 Presentation Part 2 — original pdf

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2 New technical specifications for stormwater discharges to the river Existing: Storm drainage systems causing severe erosion $$$ Proposed: Build non-erosive structures to curb damage Armored stormwater discharge infrastructure: engineering solutions designed to reduce the erosive energy from stormwater flows from developed areas to reduce erosion and related property damage and loss. 38 C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T C o l o r a d o R i v e r C o l o r a d o R i v e r Proposal: Non-Erosive Stormwater Discharges 2 New technical criteria and specifications for outfalls to river 40ft. 66" pipe C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 39 Tillery Street Storm Drain Outfall Repair Example Drop Structure for Outfall Water from surface runoff Non-erosive passage to river Armoring Col. River C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 40 Water from storm drainage system Energy of flowing and falling water entirely contained within structure Tillery St. Outfall Structure Diagram Austin’s Colony Phase 2: No Stable Channel 41 Austin’s Colony Phase 4: Stable Channel 42 Austin’s Colony Phase 4: Stable Channel 43 3 400ft Critical Water Quality Zone (CWQZ) buffer Existing: CWQZ buffer width varies from 200 to 400ft L a d y B i r d L a k e Critical Water Quality Zones: Regulatory buffers to reduce the intensity of new development directly adjacent to waterways to protect natural riparian soils and vegetation that protect water quality and flows; low-intensity uses are permitted; high-intensity uses are restricted. P u r p l e a r e a s s h o w 1 0 0 - y e a r f l o o d p l a i n s C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 44 3 400ft Critical Water Quality Zone (CWQZ) buffer Existing: CWQZ buffer width varies from 200 to 400ft L a d y B i r d L a k e *** NOT RECOMMENDED *** Existing buffers provide good protection, best fit the terrain P u r p l e a r e a s s h o w 1 0 0 - y e a r f l o o d p l a i n s C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 45 Studied: Fixed 400ft buffer width Overview of Staff Ordinance Proposal 1. 200ft Erosion Hazard Zone (EHZ) review buffer  RECOMMENDED  More accurate recognition of erosion risk  Most properties along river not impacted; not applied to hard-surfaced trails 2. New technical specifications for stormwater discharges to river  RECOMMENDED  Low-cost solution relative to much higher damage/costs 3. 400ft Critical Water Quality Zone (CWQZ) buffer  NOT RECOMMENDED  High impact on some properties; high banks not where protection needed; water quality protection more in upstream flows and larger tributaries C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 46 Schedule Since 2023 Sep./Oct. Oct. 28 Oct./Nov./Dec. Oct. 16 Nov. 6 Nov. 12 Dec. 12 Dec./Jan./Feb. Develop staff recommended ordinance Gather stakeholder input on ordinance In-Person WPD outreach meeting (Montopolis Rec. Center) Present ordinance to Commissions and Council Codes & Ordinances Joint Committee Environmental Commission Planning Commission City Council Develop/solicit stakeholder feedback on Criteria Changes Likely to be postponed; Dates TBD; check online schedule Interactive map of Erosion Ordinance C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 47 Discussion C I T Y O F A U S T I N W A T E R S H E D P R O T E C T I O N D E P A R T M E N T 48