Support for Low Impact Development

May 27, 2014

Central Texas Land/Water Sustainability Forum.

LIDGraphicNo one doubts that conventional land development impacts our creeks and lakes. Urban land development with buildings, roads, and other impervious surfaces allow less rain to soak into the ground, so the volume of runoff increases while base flow in creeks decreases. Also, urban land uses frequently incorporate rapid drainage of stormwater, and this efficient drainage can contribute to a higher peak flow downstream from a developed site. The problems produced by this “flashy” flow pattern include increased flood risks, stream channel scour, and aquatic habitat damage. Attempts to address the flooding problem (higher peak flows) by providing flood detention basins reduce peak flow rates but not the volume of runoff. Consequently, erosive flows occur for longer durations resulting in channel degradation.

Low Impact Development (LID) is a comprehensive approach to site planning, design, and pollution prevention that attempts to minimize downstream impacts of land development by matching the pre-development runoff condition and creating a more sustainable and ecologically functional landscape. Some of the many LID tools include minimizing impervious cover with permeable pavement and green roofs, capturing runoff water for beneficial reuse, and including areas called Rain Gardens that absorb more rain to compensate for impervious cover. LID is endorsed by the US EPA, the TCEQ, and is used extensively in other parts of the country. But land development regulations in central Texas evolved on a somewhat different track before LID became known.

LIDpicCity of Austin is in the process of revising the Land Development Code and Watershed Protection Ordinance to incorporate LID principles. Land development regulations are extensive and complex and making changes is a fairly long process that must involve the public. There are many challenges and technical details to be worked through. A few examples illustrate the point:

The goal of LID is maintain the natural site hydrology, including infiltration of rain into the groundwater. But as land development regulations in central Texas have evolved, another goal has been to prevent developed area runoff from entering groundwater in the Edwards and other aquifers. While this seems like a fundamental contradiction, it is a situation that should be solvable. Many practitioners recognize that the modest improvements needed in runoff quality to allow its safe infiltration into the aquifer can be addressed by passage through a layer of soil or constructed filter. Forging agreement on the details like soil/filter thickness and area will take time but should be possible if there is a commitment to LID.

When any environmental protection measure is implemented, we have an expectation that it will be maintained and continue to function as designed for a reasonable amount of time. Currently the City provides maintenance for approximately ten percent and inspection for all of the sedimentation/filtration ponds that serve residential development in Austin. To facilitate that process, the City requires these ponds to be located with public access. However, the emphasis of LID is on maintaining the pre-development runoff condition for each site. Providing City access to individual home yards may be problematic and probably isn’t necessary. But finding effective measures with an appropriate balance is complex and will require time and effort.

The LID approach can provide the central Texas area with many benefits to water resources and overall quality of life when implemented properly. One attractive benefit to a high water demand area like central Texas is that LID techniques can provide water for landscaping needs that today are primarily provided from the potable drinking water system. This potable water is treated at substantial expense and is in increasingly short supply.

While there are many advantages, adopting LID on a broad scale will require substantial changes in the way land development is currently regulated. Implementing these changes needs active involvement from all sectors of the community. The Texas Land/Water Sustainability Forum encourages the community to get involved with the City of Austin’s code revision process and support implementation of LID in central Texas.

Paul Jensen is an environmental engineer with Atkins. He is a member of the Central Texas Land/Water Sustainability Forum