The White Rock Escarpment is an ancient geological feature but only 'protected' under a city ordinance for a few decades. In 1973, Dallas was facing a large growth spurt and determined to conduct an ecological study of the entire metropolitan area. The city sought to "assess the relative significance of the city's natural environment and its tolerance to urbanization." Multiple sources were brought together to collect information on "earth, water, and life systems," map them and put them on a computerized system. Anne Whiston Spirn in "The Granite Garden" said "computer models were then designed to measure the relative tolerance of these systems to urbanization. A major benefit of the study has been the identification of the region's significant resources and hazards: headwater streams and aquifer recharge areas that are sensitive to pollution, floodplains, and the White Rock Escarpment - an area of unstable slopes and swelling soils, diverse wildlife habitat and great scenic beauty."
If anyone knows of THIS information, I'm interested.
According to Ms. Spirn, "the regulations governing development on the escarpment are based upon an understanding of earth, water, and life systems, and the interrelationships among them as well as the inferred effects of urbanization." The escarpment ordinance is a "model of sound regulations derived from an understanding of ecosystem processes."
Unfortunately, I think much of the "understanding of ecosystem processes" inherent in the derived regulations are clouded by the "effects of urbanization" and time.
Amendments to the ordinance were made to take into account the relatively new state and federal guidelines for stormwater pollution management and for coordinating best management practices on that basis. Section 51A-5.202 that prohibits any development or site alteration within the escarpment zone was not changed. There is no provision within the ordinance that would allow any new structure to be built on any portion of the area considered 'escarpment zone.'
Both the Grading Plan and the Vegetation Plan must conform to specific performance standards. The emphasis on both is for minimal disturbance of the Geological Similar Area (GSA) and to maintain the existing physical characteristics of the site where possible. The design for development should seek the 'least disturbance on the area's natural topography, watercourses, vegetation and wildlife." To emphasize that issue, the ordinance states that the protection of those areas "may preclude all development in certain areas." Existing topsoil is required to be stockpiled for later use. This would be a feature that would be helpful in almost all developments with suitable soil. Indigenous vegetation is required to be retained and protected except in areas of immediate development. If removed, similar varieties are to be replaced. Existing shrub boundaries are required to be retained.
The escarpment is a unique geologic feature for Dallas and was heavily scarred before the ordinance ever took effect with the creation of the Spur to Interstate 20. This has become a major (and highly efficient) transit route for trucking to circumvent the central core of Dallas and link back up to Interstate 35 to the north of downtown. The escarpment feature itself shows up on many of the old Dallas maps and had to be handled carefully by early travelers. Perhaps not as significant a feature to Dallas as the river that flows through it (I'll stay open to discussion on that matter), the escarpment is still a geologic wonder in Southwest Dallas that deserves respect. The purpose of the ordinance is not defined, but it was clear by the researchers who studied the science behind it, the region around the escarpment zone was treacherous and some who built before the ordinance found out the hard way. This same geological feature goes further north and south of Dallas and is a major physical feature in Waco. The escarpment and its surrounding landscapes is also favorable habitat for numerous bird species including a couple of endangered species, the black-capped vireo and the golden-cheeked warbler.
From March 5, 2008:
Article V is divided up into two divisions: the floodplain ordinance and the escarpment ordinance. This ordinance has several concepts that are not widely recognized or understood and are often sources of contention. I'd like to address a few of these concepts for your review and for further discussion later. The success and failure of the ordinance is open to debate. However, any viewpoint requires some understanding of basic concepts.
1) Escarpment ZONE - Within the ordinance, it is located ONLY south of Interstate 30 between a) the CREST side of the escarpment line and measuring horizontally from the line 125 feet, or 35 feet beyond the crest, whichever is farther from the line, and, b) the TOE side of the line and measuring horizontally from the line 85 feet from the line, or 10 feet beyond the toe, whichever is farther from the line.
2) Escarpment LINE - The line formed by the intersection of the plane of the stratigraphic contact between the Austin Chalk and the Eagle Ford shale formations and the surface of the land. This line may or may not be obvious in any particular area. One of the best places to observe the contact line is from Kiest Boulevard near the Patriot Parkway.
3) Escarpment FACE - The portion of the escarpment zone between the crest and the toe.
4) Crest - The LINE above the escarpment line where the slope becomes less than 4:1.
5) Toe - The LINE below the escarpment line where the slope becomes flatter than 5:1.
6) Geologically Similar Area - (GSA) This is a definition that is most often debated and least understood.
A) Area adjacent to and similar to the escarpment ZONE by virtue of their SLOPES, SOILS, and GEOLOGY; AND
B) The drainage basins containing the escarpment ZONE, EXCLUDING those portions of the basins which are i) downstream from the areas described in A, or ii) NORTH of Interstate 30.
7) Escarpment zone: Removing or injuring any tree or vegetation and any alteration of the physical condition of the land is an OFFENSE. There are some defenses to prosecution.
8) GSA: Removing or injuring any tree or vegetation or altering the physical condition of the land in any way is an OFFENSE without first obtaining an escarpment permit expressly authorizing the activity. There are defenses to prosecution.
9) A decision made by the director to grant or deny an escarpment permit may be appealled to the Board of Adjustment in the same manner that appeals are made from the decisions of the building official.
10) Slope Stability Analysis - For all proposed developments within the GSA, field and laboratory tests MUST be performed on samples taken from representative locations within the development site and must be certified by a registered professional engineer.
11) Soil Erosion Control Plan - MUST be submitted for all proposed development within the GSA. This would include a TIMING SCHEDULE indicating starting and completion dates of the development activities sequence and the time of exposure of each area prior to completion of control measures.
12) Development within the GSA PERFORMANCE STANDARDS:
A) MUST be fitted to the topography and soils to MINIMIZE cut and fill sections.
B) Grading is NOT permitted within the 100 year flood plain, with exceptions.
C) Indigenous vegetation MUST be retained and protected except in IMMEDIATE areas of development so that a MINIMAL amount of vegetation is removed or replaced.
D) Development MUST be accomplished in a manner which assures that as SMALL an area as possible is exposed to erosion at any one time. When land is exposed during development, the exposure MUST be kept to the SHORTEST PRACTICAL PERIOD OF TIME NOT TO EXCEED 6 MONTHS. In extraordinary cases, an extension of the six month time period MAY be granted by the director.
E) Areas where construction activities have ceased for more than 21 days MUST be stabilized by the developer to MINIMIZE erosion through the use of temporary or permanent vegetation, mulching, sod, geotextiles, or similar measures.
F) Temporary vegetation and mulching MUST be used to protect areas exposed during development.
There are ELEVEN total standards listed in the ordinance.
13) Development within the GSA GRADING STANDARDS
A) Grading must be PLANNED so as to have the LEAST disturbance on the area's natural topography, watercourses, vegetation, and wildlife. This MAY preclude ALL development in certain areas.
B) Topsoil MUST be stockpiled and redistributed on areas where vegetation will be grown after the grading is completed.
There are THREE total standards listed in the ordinance.
14) Development within the GSA VEGETATION STANDARDS
A) Indigenous vegetation MUST be retained and protected EXCEPT in IMMEDIATE areas of development so that a MINIMAL amount of vegetation is removed or replaced.
B) Shrub borders MUST be maintained around woodlands where practicable.
There are THREE total standards listed in the ordinance.
15) Platting: The property owner is encouraged, but not required, to dedicate the escarpment zone or GSA to the city as a park.
1) Escarpment ZONE - Within the ordinance, it is located ONLY south of Interstate 30 between a) the CREST side of the escarpment line and measuring horizontally from the line 125 feet, or 35 feet beyond the crest, whichever is farther from the line, and, b) the TOE side of the line and measuring horizontally from the line 85 feet from the line, or 10 feet beyond the toe, whichever is farther from the line.
2) Escarpment LINE - The line formed by the intersection of the plane of the stratigraphic contact between the Austin Chalk and the Eagle Ford shale formations and the surface of the land. This line may or may not be obvious in any particular area. One of the best places to observe the contact line is from Kiest Boulevard near the Patriot Parkway.
3) Escarpment FACE - The portion of the escarpment zone between the crest and the toe.
4) Crest - The LINE above the escarpment line where the slope becomes less than 4:1.
5) Toe - The LINE below the escarpment line where the slope becomes flatter than 5:1.
6) Geologically Similar Area - (GSA) This is a definition that is most often debated and least understood.
A) Area adjacent to and similar to the escarpment ZONE by virtue of their SLOPES, SOILS, and GEOLOGY; AND
B) The drainage basins containing the escarpment ZONE, EXCLUDING those portions of the basins which are i) downstream from the areas described in A, or ii) NORTH of Interstate 30.
7) Escarpment zone: Removing or injuring any tree or vegetation and any alteration of the physical condition of the land is an OFFENSE. There are some defenses to prosecution.
8) GSA: Removing or injuring any tree or vegetation or altering the physical condition of the land in any way is an OFFENSE without first obtaining an escarpment permit expressly authorizing the activity. There are defenses to prosecution.
9) A decision made by the director to grant or deny an escarpment permit may be appealled to the Board of Adjustment in the same manner that appeals are made from the decisions of the building official.
10) Slope Stability Analysis - For all proposed developments within the GSA, field and laboratory tests MUST be performed on samples taken from representative locations within the development site and must be certified by a registered professional engineer.
11) Soil Erosion Control Plan - MUST be submitted for all proposed development within the GSA. This would include a TIMING SCHEDULE indicating starting and completion dates of the development activities sequence and the time of exposure of each area prior to completion of control measures.
12) Development within the GSA PERFORMANCE STANDARDS:
A) MUST be fitted to the topography and soils to MINIMIZE cut and fill sections.
B) Grading is NOT permitted within the 100 year flood plain, with exceptions.
C) Indigenous vegetation MUST be retained and protected except in IMMEDIATE areas of development so that a MINIMAL amount of vegetation is removed or replaced.
D) Development MUST be accomplished in a manner which assures that as SMALL an area as possible is exposed to erosion at any one time. When land is exposed during development, the exposure MUST be kept to the SHORTEST PRACTICAL PERIOD OF TIME NOT TO EXCEED 6 MONTHS. In extraordinary cases, an extension of the six month time period MAY be granted by the director.
E) Areas where construction activities have ceased for more than 21 days MUST be stabilized by the developer to MINIMIZE erosion through the use of temporary or permanent vegetation, mulching, sod, geotextiles, or similar measures.
F) Temporary vegetation and mulching MUST be used to protect areas exposed during development.
There are ELEVEN total standards listed in the ordinance.
13) Development within the GSA GRADING STANDARDS
A) Grading must be PLANNED so as to have the LEAST disturbance on the area's natural topography, watercourses, vegetation, and wildlife. This MAY preclude ALL development in certain areas.
B) Topsoil MUST be stockpiled and redistributed on areas where vegetation will be grown after the grading is completed.
There are THREE total standards listed in the ordinance.
14) Development within the GSA VEGETATION STANDARDS
A) Indigenous vegetation MUST be retained and protected EXCEPT in IMMEDIATE areas of development so that a MINIMAL amount of vegetation is removed or replaced.
B) Shrub borders MUST be maintained around woodlands where practicable.
There are THREE total standards listed in the ordinance.
15) Platting: The property owner is encouraged, but not required, to dedicate the escarpment zone or GSA to the city as a park.
Desert Vision by David Lanz
Posts
0 comments:
Post a Comment