DEPARTMENT: Development Services
SUBJECT: TPV 17-005 Tree Preservation Variance for Stinson Municipal Airport - Air Traffic Control Tower
SUMMARY:
Request by Mr. Loyce D. Clark, for approval of a tree preservation variance request from Unified Development Code 35-523 (h), “significant trees shall be preserved at eighty (80) percent and heritage trees at one hundred (100) percent preservation within both the 100-year floodplains and environmentally sensitive areas.” With 45% tree stand preservation in the environmentally sensitive area, mitigation to the required 80% will be met by preservation of small species and understory vegetation, implementing LID BMP’s, re-seeding disturbed areas with native seed mixes, and planting trees to meet tree mitigation requirements. (Mark C Bird, (210) 207-0278, mark.bird@sanantonio.gov, Development Services Department)
BACKGROUND INFORMATION:
Project A/P# A2054783
Council District: 3
Consultant: Laurie Hawkins, J & L Consulting LLC
Staff Coordinator: Mark C Bird, City Arborist, (210) 207-0278
ANALYSIS:
The Development Services Department (DSD) has reviewed the information presented in Mr. Loyce D. Clark’s letter submitted December 19, 2016. The proposed Stinson Airport Control Tower facility is required for the safety and wellbeing of the public and is designed to meet the current and future air traffic controls needs as well as the FAA Orders that govern such structures. The Unified Development Code (UDC) - Article V, Section 35-523 (h), 100-Year Floodplain(s) and Environmentally Sensitive Areas states that, “Significant trees shall be preserved at eighty (80) percent preservation within both the 100-year floodplains and environmentally sensitive areas.”
The applicant wishes to remove significant tree stand in excess of the 80% minimum preservation requirements for significant trees and 100% heritage tree preservation for environmentally sensitive areas. DSD staff does agree with the applicant’s request to mitigate for below 80% preservation of significant trees and 100% heritage tree preservation in the environmentally sensitive areas for the following reasons:
1. Due to requirements of the Federal Aviation Administration (FAA) Orders that govern the specifications to obtain a clear line of sight for the proposed new air traffic control tower to ensure an unobstructed line of sight to all airport movement areas of tree canopy will require removal. For the structure to meet the FAA order trees will be removed in excess of the minimum floodplain 80% preservation for significant trees and 100% preservation for heritage trees. Proposed preservation for significant trees in the floodplain is 45%. Heritage trees will be preserved at 23%.
2. The proposed new Stinson Airport air traffic control tower (ATCT) facility is required for the safety and wellbeing of the public. It has been designed to meet the current and future air traffic control needs as well as the FAA Orders that govern such structures.
3. The Airport Master Plan which began in 2011 included a Safety Risk Management Plan Process that reviewed alternative control tower designs and locations based on FAA and OSHA standards/requirements in addition to historical and archaeological constraints, including the Mission Parkway Historic Archeological District as well as environmental impacts to floodplain and tree preservation. The location of the ATCT was selected for meeting criteria sensitive to all historic, archaeological, and environmental concerns and to preserve as many trees as possible.
4. An initial assessment of the project called for the total clearing of two (2) acres of trees to provide an unobstructed view. However, a tree assessment performed by ISA Certified Arborists determined that only tall large species trees will be removed and other trees above certain heights (15 feet) would be removed. This allows the preservation of understory small species trees and native low growing shrubs, grasses and other vegetation to remain.
5. Significant and Heritage tree mitigation for removal of trees below minimum preservation in the floodplain and floodplain buffer areas include: 1) re-seeding disturbed areas with native species grass mixes, planting native grass bare roots to ensure quicker stabilization in riparian area. The native grass species selection focused on root system capability (15 foot depth) especially for bank stabilization for riparian and steep-slope upland areas. The species mix will grow together to hold down soils then naturally rebuild the soil 2) Planting four (4) new native medium species trees for parking lot shading 3) Implementation of 3,117 square feet of LID BMP’s (vegetative filter strip, grassy swale, and rain garden per LID Design Guidance Manual-SARA).
DSD staff supports the applicant’s request of the environmental variance from UDC 35-523 (h) to allow for mitigation in environmentally sensitive areas for the construction of the Stinson Municipal Airport Air Traffic Control Tower facility.