Civil Engineering

Water Quality Success for LOWE's Southwest Austin Store

In June of 2003, Cunningham-Allen, Inc. (CA) was retained to work in conjunction with the project Civil Engineer on the design and permitting of the new Lowe’s store in Southwest Austin.

The project site is in the Edwards Aquifer Recharge Zone and in the Barton Springs SOS Zone. These are environmentally critical areas established by the Texas Commission on Environmental Quality (TCEQ) and the City of Austin (COA), respectively, and require additional water quality measures and permitting.

In particular, the Barton Springs SOS Ordinance imposed a “zero degradation” standard to storm water quality, meaning that water quality measures had to ensure that the quality of the storm water runoff flowing over the improvements has been returned to its pre-development condition before it is released from the site.

CA was very familiar with these design requirements because we had worked with the City of Austin on developing water quality measures for one of the first projects that had to comply with this new ordinance.

For the LOWE’S project, we worked in conjunction with the project Civil Engineer and designed a system that collected all the storm water that runs off the impervious cover (such as roofs and parking lots) and directed it to a retention basin. Storm water is allowed to settle in the retention basin for 12 hours, then it is pumped via a pumping system to be irrigated over an area of the site that had been dedicated for this purpose and left undisturbed. The size of the irrigation area was calculated based on the estimated volume of runoff (or water quality volume) and the estimated soil infiltration rate such that the entire water quality volume infiltrates the soil and is naturally treated through the existing vegetation’s root system and other microorganisms. As an additional measure of safety, berms were constructed downstream of the irrigation field such that runoff, if any, is captured and recycled through the retention pond and irrigation system.

This design, known as a “retention/re-irrigation system” was submitted to the COA and was approved with minor modifications.

As mentioned above, the project was also under TCEQ’s jurisdiction, which required specific permitting for storm water and wastewater. CA prepared the necessary permit applications and assisted the Owner in securing these approvals as well.

Finally, CA was excited to participate with the Owner, the project Architect, and the Civil Engineer on this project to assist them in securing a Bronze Certificate for LEED design (Leadership in Energy and Environmental Design) based on the innovation and effectiveness of the water quality system.

Introduction to Zoning in the City of Austin

 

 

One of the first steps in the entitlement process within the City of Austin consists of zoning. Zoning imposes requirements, limitations, and restrictions for a property and defines “ranges” in uses. Residential, commercial, and industrial base districts are arranged in a hierarchy that begin with the Lake Austin (LA) base district as the most restrictive and ends with the Limited Industrial (LI) base district as the least restrictive district.

The purpose for zoning is compatibility in the most simplistic definition. A buyer or developer wants to know what is planned around them if they are investing in a property. This extends the spectrum whether one purchases a home or a commercial property. It’s more of “insurance” to know whether a home will be abutting a supermarket (commercial use), a school, a greenbelt, or another home in the future.  

Zoning defines what can be situated on the property.  There are allowable uses that can be placed on a zoning district that are more restrictive. I referred to these as “ranges” in uses. More often than not the allowable uses in less restrictive zoning districts are usually grandfathered structures/uses. Thus, allowable uses must be taken into account when determining restrictions based on zoning. An example would be a residential home located on a commercially zoned property. If the surrounding properties are all commercially zoned, the residential home would be considered as the more restrictive single family (SF) zoning.  

The City of Austin’s zoning (chapter 25-2 in the Land Development Code) does account for such cases, so the code must be delved into in order to determine the impacts on the property one is developing or rezoning based on the surrounding zoning and land uses. Thus, when you are buying or developing a property it is necessary to investigate not only the zoning and range of uses of your property, but also the surrounding properties.

by Rubén López, Jr., P.E.

Development using Commercial Design Standards, Part 1

Commercial Design Standards have been a part of the City of Austin Design process for several years.  Cunningham-Allen embraces the concept of the standards and think there are many ways of complying with the intent of the ordinance while continuing to achieve our clients’ goals by producing a project of excellent quality.  This is the first part of several upcoming articles about the Design Standards.  

How do you determine how the Commercial Design Standards (CDS) will impact your project?

If your property is located within the Austin City Limits, you will probably be affected by the Commercial Design Standards unless your property falls under some of the exemptions which include:

  • development in a Traditional Neighborhood district,

  • development built prior to the overlay provisions of the university neighborhood overlay district, or

  • development built prior to an adopted transit station area plan.

The first thing a property owner should do when designing the project site plan is to determine exactly how many of the CDS apply to the particular project by asking some of the following questions:

  • What land use is being proposed?  

If the project is single family residential, it is exempt from this ordinance.  Any other use: commercial, office, multifamily, or industrial will all require compliance with all or varying parts of the standards.

  • What type or types of “roadway or roadways” as defined by the standards, provide access to the project and what happens if the project is fronted by more than one roadway?

The impact of each of the varying roadway types on which your property has frontage determines the relationship of buildings to streets and walkways; whether you will have to “pull” your building up to the property line with room for sidewalks and tree/furniture zones, or whether you can have parking located between the street and the building.  If your site has frontage on more than one type of roadway, the highest level of roadway is the roadway that determines your building and parking placement.

There is a hierarchy of street types listed in the Design Standards.  The most important to least important in the city’s design strategy is as follows:  Core Transit Corridor, Internal Circulation Route, Urban Roadway, Suburban Roadway and Highway or Hill Country Roadway.  There are several maps at the beginning of the Commercial Design Standards section that depict Core Transit Corridors, Future Core Transit Corridors, Urban Roadways and Suburban Roadways of the city.  

  • Core Transit Corridor:  If your project fronts on a Core Transit Corridor, it means the property is located on a street that the city has determined to be a roadway with enough population to encourage transit use and therefore, the relationship of buildings to the streets and walkways is of great importance.  City of Austin - Core Transit Corridors

  • Internal Circulation Routes:  Any public or private street in a development.

  • Urban Roadway:  Any street that is not a Core Transit Corridor that is located in the center of the Austin City Limits as shown on Figure 1 of the Design Standards (See Image).

  • Suburban Roadway:  Any street that is not a Core Transit Corridor that is located outside the boundary of the Urban Roadway area.

  • Highways:  Includes all the freeways, expressways, parkways and frontage roads listed in the Austin Metropolitan Roadway Plan, except for Core Transit Corridors.

  • Hill Country Roadways:  If your project fronts on a Hill Country Roadway as defined by the list of Hill Country Roadways within the Design Standards, the first 1000 feet of your project will have to comply with Hill Country Roadway standards of the Land Development Code in conjunction with the Commercial Design Standards.

For example, if your site is located on Lamar Boulevard, your site faces a Core Transit Corridor.  Building placement on a Core Transit Corridor requires the creation of a 15 foot wide sidewalk and tree/furniture zone between the street and building, to provide an environment that is supportive of pedestrians.

If your site is located on a suburban roadway, public sidewalks are required but you have choices as to whether to place your building adjacent to the sidewalk and street or to have parking between the sidewalk and building.  If you choose to “pull” your building up to the sidewalk and locate the parking behind and beside the building, you will be exempt from connectivity requirements.  Connectivity is described as the internal circulation system for a large site.

At this point, the size of the site (number of acres) will help make the location decisions of the building and parking with reference to the roadway frontage.  If your site is five acres in size or larger, you may choose to design the site with buildings fronting on internal circulation routes created by dividing the site into blocks no longer than 660 feet by 330 feet.  On sites larger than 15 acres, the site may have one block with a maximum dimension of 660 feet by 660 feet for each 30 acres.  Corporate Campuses are exempt from the maximum block length requirement.

The following sketches illustrate some of the possibilities of building placement along some of the different types of roadways and along the internal circulation route of a larger site.

Remember, the goal of the Commercial Design Standards is to provide guidelines enhancing each project and helping create a community with multiple land uses, utilizing pedestrian access to provide enjoyable living environments.

Next time we will discuss more specifics about building placement and building design requirements.

Making a Middle School into a High School

In 2007, Dripping Springs Independent School District’s (DSISD) Bond included a recommendation to convert the existing High School to a new Middle School and to expand and convert the existing Middle School to become the new High School. This was based on a two-year long study conducted by the DSISD’s Long Range Facilities Planning Team consisting of 74 community members representing every part of the school district attendance area, including parents, grandparents, business owners, teachers, principals, district administrators and support staff, board members, retired community members, and consultants.

Cunningham-Allen, Inc. was honored to be selected to work on both conversion projects and provide Surveying and Civil Engineering services.

There was one stipulation:  Both projects had to be completed without ANY interruption of classes or other school services

The construction operations had to be carefully scheduled and coordinated with the school schedule and design required the facilities and services (water, wastewater, drainage, and parking) to be phased to achieve a conversion without service interruption.

As you would expect, both projects presented several challenges.  However the civil engineering challenges we faced converting the existing Middle School to the new High School were truly unique, especially the design of the wastewater service.

The existing Middle School was designed for 1,200 students and occupied a 40 acre site including an on-site wastewater treatment plant (WWTP). The new High School was to house 1,800 students, with a future capacity of 2,500 students. The district purchased an additional 60 acres to accommodate the additional facilities associated with a High School campus. Due to the significant increase in population and the planned expansion of the existing building, the existing on-site wastewater treatment plant had to be abandoned, completely redesigned at a different location and permitted to meet current State of Texas code.

As the design of the new on-site WWTP was underway, the team learned there was a possibility the City of Dripping Springs could provide wastewater service to the school. This option was attractive to DSISD since it was more economical and would eliminate substantial maintenance and operation costs associated with an on-site wastewater treatment plant.  In order to connect the school’s wastewater lines to the City’s system, a different wastewater collection system would have to be designed and constructed.

DSISD and the City of Dripping Springs started the necessary negotiations immediately, but it became clear the time needed to reach a final agreement might take longer than the planned opening date of the new High School.

A reverse schedule was prepared, starting from the opening date and listing the major design, permitting and construction milestones and “drop dead” decision dates that would have to occur for either of the wastewater options to be in place by opening day.  Based on that reverse schedule, DSISD decided to proceed with the design and construction of both options until the final agreement between the District and the City had been reached.

By the time the agreement between the City and the District was reached to use the City’s wastewater system, the on-site wastewater treatment plant had been completely designed and permitted, and the majority of the on-site wastewater infrastructure had been constructed. Luckily, no construction on the on-site wastewater treatment plant had started.

The coordination of the design, construction, and school schedule was very challenging with a looming, unchangeable opening date. In the end, having a team that was willing to work together toward one goal paid off. The entire project was constructed on schedule, on budget, and without one day of missed school – much to the dismay of the students!

Ponds: Why do I need one? What are my choices?

If you are going to develop land around the City of Austin, you need to be aware of how important water quality is.  Below is a list of parameters you need to follow depending on the metrics of your development.

  • Water quality is required in the City of Austin when a development site exceeds 20 percent impervious cover using the net site area of your site (LDC 25-8-211).  
  • If you are in the Barton Springs Zone water quality is required for all development.  
  • The Texas Commission for Environmental Quality (TCEQ) requires water quality when development takes place over the Edwards Aquifer.   
  • The standards for design and construction of these water quality controls come from the Land Development Code and the Environmental Criteria Manual of the City of Austin.  
  • If the development is outside the City of Austin but over the Edwards Aquifer, TCEQ standards apply.  
  • When developing inside the City of Austin and over the Edwards Aquifer typically you can follow the City of Austin standards and your finished pond will meet the standards of TCEQ as well.  However, calculations must be shown by both standards to the respective reviewing entity.  

The list above explains why you need a pond, but what choices do you have to construct?  Two of the more common choices are a sediment and filtration pond or a wet pond.  

The sedimentation and filtration (sed-fil) pond is made up of a sedimentation basin or chamber and a sand filtration bed.  The basin and bed are separated by a rock gabion wall which is used to block large trash from entering into the sand filtration bed.  The “first flush” runoff (required to be cleaned by the City of Austin) enters the sedimentation part of the pond where large particles and trash settle to the pond bottom.  The sand media cleans the pre-determined amount of runoff as it percolates through and into perforated under-drain pipes.  The clean runoff is then released from the filtration part of the pond until the entire pond is empty.  

A wet pond gets its name from its nature; always being full of water.  This fundamental difference is used by developers as an aesthetic benefit and used by engineers as a way to clean the runoff from the site before it returns to the environment.  The forebay acts in a similar way as the sedimentation basin of a sed-fil pond.  The main pool is separated from the forebay by an earthen berm.  A substantial portion of the pollutant removal in wet ponds is due to biological processes caused by the plants that border the pond.

From a cost and constructability standpoint, a sed-fil pond is typically less intensive.  They are typically the water quality control of choice for commercial, multi-family, and school development.  Wet ponds tend to become desirable when serving larger single family developments, in which case they also serve as an aesthetic benefit to home buyers.