20240821-003: Infill Plat Site Plan-Lite Watershed Protection Presentation UPDATED — original pdf

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Infill Plats & Site Plan Lite, Part 2: Overview of Drainage Elements of Staff Proposal Environmental Commission | August 21, 2024 Watershed Protection Staff Presentation Outline • Council direction Three different development processes • • Non-zoning requirements • The continuum question • • • Flood detention The ordinance’s drainage proposal Storm drain connection proposal • Summary • Questions Council Direction Resolutions 20230504-023 and 20221201-048: • Propose streamlined development processes scaled for small residential subdivisions and multifamily projects with 5 to 16 units • “create a site plan review process tailored appropriately for missing middle housing, with fewer requirements than that of full site plan review • “holistically review all existing non-zoning development requirements for value and impact in application to missing middle projects, including but not limited to drainage and water quality, parking and street impact fees, parkland dedication, trees, and utilities…. with the goal of streamlining review in a manner scaled to the impacts of development” Development Process Steps to build housing and other developments: 1. Residential Subdivisions (to create the lots for building permits) 2. Site Plans (for multifamily residential projects, including missing middle) 3. Building Permits (for 1 to 3 residential units on one lot) • Each path has separate code and processes • Building permits are much simpler and more streamlined than the others Building Permit (BP) • Follows subdivision in the order of the development process • Is the vehicle to build 1 to 3 houses on an existing, platted lot • Features relatively small-scale projects with more streamlined permitting process • SF-1, SF-2, and SF-3 zones have impervious cover limits of 45% • Requires the following to guide drainage design: o Building Code o Plumbing Code o Texas State Law o Land Development Code: floodplain and erosion hazard zone • Has less demanding drainage requirements than subdivision—e.g., no storm drain system analysis or detention required—since these are assumed to take place at the preceding subdivision phase Residential Subdivisions • Precedes building permits in the order of the development process • Creates multiple platted lots, on each of which 1 to 3 homes can be built using a building permit • Traditionally large-scale projects with full, more complex permitting process • Watershed impervious cover limits are considered at this phase • Larger projects include roads and utility infrastructure • Requirements include storm drain system analysis and flood detention • Existing regulations designed for and work best for larger subdivisions • Current code not intended for very small subdivisions at the scale now possible with HOME-2. Subdivision with platted lots Creates individual platted lots; building permit projects follow later 0.25-acre scale relevant to infill plat ordinance Site Plans • Use an individual platted lot from a prior subdivision • Used for missing middle and multifamily residential (if have appropriate zoning) • Zoning code guides how many residential units can be built on a given tract • Missing middle zones typically have impervious cover limits of 60 or 65% • Traditionally larger-scaled projects (than residential building permits) with full, more complex permitting process • Drainage requirements include storm drainage analysis and detention • Regulations designed for and work best for larger subdivisions • Current code not intended for very small subdivisions at the scale now possible with HOME-2. Missing Middle Example Building units Stormwater drainage Non-Zoning Requirements • Council asked staff to look at “non-zoning development requirements” • Affect the cost and feasibility of housing projects • Not all are in the Land Development Code—many are in criteria or • Separate efforts outside of this ordinance will examine these other • Flood detention is in the code and is a major cost and complexity processes elements element Non-Zoning Requirements • Building permits: relatively fast and uncomplicated; no detention o One example estimate: approx. 1-2 month timeline and $30K to process • Small-scaled subdivisions cost much more and take much longer o Estimated 12-24 months and $340 to 365K to design and permit • These two example products were functionally identical: same number of units, impervious cover, etc. • Flood detention and drainage made up 20 to 40% of this cost • The Council requests staff propose new code and processes to make these two products more similar in cost, complexity, and permitting time The Continuum Question “Across the continuum of projects sizes, when is a project too small to apply flood detention?” • Water quality controls: required for projects with 8,000 sq. ft. or more of impervious cover (Land Development Code 25-8-211) • Flood detention: no limit set in code • De facto lower detention limit for subdivisions: historic min. lot size of 5,750 sq. ft. x 2 lots = 11,500 sq. ft. = 0.264 acres • This was the smallest subdivision size prior to HOME 2 (with very minor exceptions)—about 0.25 acres in size • Subdivisions require full storm drain system analysis & flood detention Impervious Cover Flood Detention • Critical stormwater management tool; used since 1974; 5K+ (and counting) • Used to reduce peak storm flows and downstream flooding • Originally designed for large site-plan and subdivision projects • Work underway to expand our detention requirements • But not required for individual single-family building permits • Staff do not recommend detention for small HOME-2 projects o Benefits anticipated to be marginal/solution doesn’t scale… add cost/complexity o Multiple permitting, maintenance, inspection, and longevity concerns o Recommend the current de facto 0.25-acre size be the minimum size The Ordinance’s Drainage Proposal • Draft proposal scales to project type, size, and topographic complexity • Apply the same drainage requirements for tiny subdivisions as we do for residential building permits; same scale/product, use same approach o No detention required for projects up to 0.25 acres in size • Provide 3 tiers of compliance for subdivisions up to 1 acre maximum • Tiered options for small-scaled multifamily projects, but no minimum for potential detention (higher impervious cover, more runoff) • Complementary to existing Drainage Criteria Manual rules for detention alternatives for small sites • No changes to impervious cover limits Summary of Infill Plat Proposal What Required Details Discussion Pre-Project Size <=0.25 acre N/A No requirements (beyond Building Code and State Law) Must clearly drain to Right-Of-Way (ROW) or Storm Drainage System Similar scale to existing Residential Permits Drainage map with flow direction arrows No RSMP payment; PE not required; show runoff follows existing patterns >0.25 - 1.0 acre Grade to drain to ROW or Storm Drainage System DCM 1.2.2.G./RSMP with payment PE required; review and inspection to ensure grading completed Detention Full code & criteria Use Site Plan Exemption >1.0 acre Full Drainage Requirements Full code & criteria Full code & criteria (e.g., DCM Section 8) DCM = Drainage Criteria Manual; PE = Professional Engineer; RSMP = Regional Stormwater Management Program Pre-Project Size <=0.5 acre >0.50 - 1.0 acre Summary of Site Plan Lite Part 2 Proposal What Required Details Discussion Must clearly drain to Right-Of-Way (ROW) or Storm Drainage System Drainage map with flow direction arrows No RSMP payment; PE not required; show runoff follows existing patterns Grade to drain to ROW or Storm Drainage System DCM 1.2.2.G./RSMP PE required; review and inspection to ensure grading completed Detention Full code & criteria Full code & criteria Grade to drain to ROW/ Storm Drainage System DCM 1.2.2.G./RSMP Expanded DCM 1.2.2.G eligibility (5-14 unit multi-family/65% IC max); PE required Detention Full code & criteria Use Site Plan Exemption >1.0 acre Full Drainage Requirements Full code & criteria Full code & criteria (e.g., DCM Section 8) DCM = Drainage Criteria Manual; PE = Professional Engineer; RSMP = Regional Stormwater Management Program Storm Drain Connection Requirement • WPD staff propose to initiate an amendment to the Drainage Criteria Manual that would achieve the following: 1) Require connection to an existing storm drain system only for development located within 300 feet, rather than 550 feet 2) Eliminate connection requirement altogether, regardless of distance, if: The site does not exceed 0.50 acres; or • • For sites up to one acre, the applicant demonstrates that street, gutter, and storm drain inlet contains the 100-year fully-developed flow rates for the applicable drainage area RSMP Amendment • WPD staff propose to initiate an amendment to the Drainage Criteria Manual that would allow projects of up to 5-16 units per acre to participate in the Regional Stormwater Detention Program (RSMP) if they do not exceed 1 acre in area • • This would allow some sites (depending on topography) to use alternatives in lieu of onsite detention Such projects would participate in the RSMP, would be required to be designed and sealed by a professional engineer, and would have extensive staff review Summary • Establishes “right-sized” drainage regulations for small, infill housing subdivisions and The proposed ordinance: missing middle projects up to 1-acre in size • Does not change impervious cover limits • Uses a tiered approach based on project type, size, and topographic complexity • Small subdivisions at or under 0.25-acre would not be required to provide drainage solutions beyond those required for housing using building permits at the same scale • Is only eligible for sites previously platted as a residential subdivision • Is complemented by two Drainage Criteria Manual amendments supporting the above Questions?