Stormwater and Drainage
Overview of Information
According to FEMA, the 1964 flood is Boerne’s most damaging rainfall event and remains the flood of record.
Based on FEMS's guidelines, there is a two percent chance a storm of that magnitude can occur annually.
The flood caused the highest water rate in the creek’s recorded history at 36,400 cubic feet per second. Previously, this would have been classified as a “50-year” flood.
That historic storm led to the planning and development of ways to prevent future catastrophic flooding, which ultimately created four Soil Conservation Service sites – water retention dams – north and west of Boerne to serve as flood control. In January 1972, the Texas Water Commission granted permission to the City of Boerne to construct and maintain a dam on Cibolo Creek for municipal purposes to aid in flood control. Boerne Lake is the largest of the four SCS’s constructed after the flood of 1964. More than seven years later, the certificate was amended so the city could utilize water from the reservoir for domestic purposes and in 2005 City Lake Park was developed.
While the uses of Boerne Lake have increased over the years, it was first and foremost a flood control structure. In total, the four SCS’s hold approximately 21,800 acres of watershed. In the City of Boerne, approximately 32,000 acres of watershed ultimately funnels into River Road Park, in downtown Boerne. Of that 24,400 acres of watershed occur outside of city regulations.
Past Drainage Master Plans
- 1968: Watershed Work Plan – resulted in the building of four water control dams.
- 1991: Drainage Master Plan
- 2002: Updated Drainage Master Plan
- Updated subdivision ordinance
- Proposed creating a stormwater utility (passed by City Council in 2019). As of 2021, the stormwater utility is billing customers within the city limits $50,000/month. This money can only be used to water and drainage within the city limits.
- Develop model for Currey Creek and No-Name Creek
- Prepare plan for improvements, as well as finance and implement improvement plans
- 2021: Updated Drainage Master Plan
- Citizens Flood Map: allowed residents to pinpoint trouble spots in need of upgrades.
- City staff is thinking of creative and adaptive ways to update flood prone areas that fit with the Hill Country esthetic and resident’s desires
Development Code Changes
- Subdivision Ordinance – February 2020
- Created Drainageway Protection Zones and Local floodplain requirements to include areas not included in the federal flood maps. For example, previous FEMA floodplain maps stopped at Adler Road, the updated ordinance now includes watershed north of that area.
- Provide more detail on Low Impact Development requirements
- Flood Damage Prevention Ordinance – August 2020
- Greater restrictions on residential within floodplains
- Finished Floor (FF) height changes
- Net storage volume requirements, which means if a development changes the conditions of a water way, the developer must accommodate for that change so there is a net-neutral impact.
- UDC – July 2021 (tentative)
- Changes to residential cross property drainage requirements
- Detailed requirements for residential mass grading
- Further detail on detention pond design
- Groundwater recharge feature protection
- Enhanced erosion protection requirements
- City is not a regulated Municipal Separate Storm Sewer System (MS4) therefore erosion control enforcement is by Texas Commission for Environmental Quality region office. According to the TCEQ, an urbanized area is a densely settle core of census tracts or census blocks that have a population of 50,000 or more. It is a calculation used by the U.S. Census to determine the geographic boundaries of the most heavily developed and dense urban areas.
- Phase II (small) MS4’s are established for areas located within Urbanized Area (UA) and outside the UA but designated by TCEQ.