Florida Watershed Journal Low-Impact Development : Page 1

WINTER 2011 Volume 4 • Issue 1 1 ________________________ Low-Impact Development Comes to Florida Jack Merriam 7 ________________________ Modifying Low-Impact Development Practices for Florida Watersheds Justin Gregory, P.E. Brett Cunningham, P.E. Laura Ammeson Mark Clark, Ph.D. H. Clark Hull Jr. 12 ______________________ Implementing Low-Impact Development in Florida: Practitioners’ Perspectives Low-Impact Development Comes to Florida Jack Merriam, Environmental Manager Sarasota County Integrated Water, Sarasota County, FL Introduction Low-Impact Development (LID) came to Florida more than 20 years after it was first conceived in Prince George’s County Maryland starting with bioretention in the 1980s/90s. (Prince George’s County, 1993). The County subsequently published an LID design manual with a grant from the United States Environmental Protection Agency (USEPA) (Coffman, Larry 2000). One of the earliest uses of LID in Florida was the design and construction of the parking lot at the Florida Aquarium in Tampa. This was built with a grant from the Southwest Florida Water Management District (SWFWMD) and Department of Environmental Protection, included pervious and impervious parking for comparison purposes and vegetated and paved swales or strands again for comparison purposes, and was monitored for 2-3 years by Dr. Betty Rushton, then with SWFWMD. In 2004 the Tampa Bay Regional Planning Council even hosted a conference on LID in an effort to bring LID to Florida. What is LID? Perhaps one definition would be to characterize it as biomimicry in that it is a method of developing, redeveloping, or retrofitting that seeks to mimic the natural hydrologic regime as closely as possible. Another simple definition used recently is that LID causes “run-in” rather than “run-off,” since it incorporates a treatment train approach of small distributed Best Management Practices (BMPs) which tend to cause rainfall to run into depressions such as rain gardens, bioretention areas, bioswales, or even into cisterns and other storage. These collectively accomplish infiltration, storage, rainfall interception, reuse, bioremediation, and evapotranspiration, all with the goal of minimizing runoff or increases in the volume of water discharged from a site after development. Many of the “new” techniques of LID are really old techniques relearned. These include things from the past such as sod roofs or other vegetated roofs such as are described in the Hanging Gardens of Babylon, brick streets, and cisterns to capture rainfall. It also includes site planning and design including selection of a building lot because of its natural amenities, planning and designing of all infrastructure for preserving the natural vegetation to take advantage of cooling and rainfall interception by trees, and building houses on piers or stemwalls instead of clearing and filling the entire lot. While LID was embraced around the country and indeed around the world, it has been slow to come to Florida. Florida has been slower to embrace it for several reasons. First, we have very different physical conditions—rainfall, geology, hydrology including high water tables in some parts of the state—from many other areas, and we have five quasi-independent water management districts with different permitting requirements. The perception has been that while LID may work in Prince George’s County or Portland, Oregon, it will not work here because of our unique conditions. This issue of the Journal offers papers that demonstrate that Florida is now developing the research and practical knowledge to adapt LID techniques for Florida conditions so that design professionals and Continued on page 4 M. Jennison Kipp, M.S. Christina E. Lathrop, ASLA, LEED AP Mark E. Hostetler, Ph.D. Mark W. Clark, Ph.D. Pierce H. Jones, Ph.D. 19 ______________________ Consideration Of Low-Impact Development Benefits In Beaufort County, South Carolina Richard A. Wagner, P.E., D. WRE Robert E. Klink, P.E. Dan Ahern, P.E., BCEE 23 ______________________ Infiltration Gallery: Conventional Design, Contemporary Performance Evaluation Mike Gregory, P.E.

Low-Impact Development Comes To Florida

Jack Merriam

Low-Impact Development (LID) came to Florida more than 20 years after it was first conceived in Prince George’s County Maryland starting with bioretention in the 1980s/90s.(Prince George’s County, 1993). The County subsequently published an LID design manual with a grant from the United States Environmental Protection Agency (USEPA) (Coffman, Larry 2000). One of the earliest uses of LID in Florida was the design and construction of the parking lot at the Florida Aquarium in Tampa. This was built with a grant from the Southwest Florida Water Management District (SWFWMD) and Department of Environmental Protection, included pervious and impervious parking for comparison purposes and vegetated and paved swales or strands again for comparison purposes, and was monitored for 2-3 years by Dr. Betty Rushton, then with SWFWMD. In 2004 the Tampa Bay Regional Planning Council even hosted a conference on LID in an effort to bring LID to Florida.

What is LID? Perhaps one definition would be to characterize it as biomimicry in that it is a method of developing, redeveloping, or retrofitting that seeks to mimic the natural hydrologic regime as closely as possible. Another simple definition used recently is that LID causes “run-in” rather than “run-off,” since it incorporates a treatment train approach of small distributed Best Management Practices (BMPs) which tend to cause rainfall to run into depressions such as rain gardens, bioretention areas, bioswales, or even into cisterns and other storage. These collectively accomplish infiltration, storage, rainfall interception, reuse, bioremediation, and evapotranspiration, all with the goal of minimizing runoff or increases in the volume of water discharged from a site after development. Many of the “new” techniques of LID are really old techniques relearned. These include things from the past such as sod roofs or other vegetated roofs such as are described in the Hanging Gardens of Babylon, brick streets, and cisterns to capture rainfall. It also includes site planning and design including selection of a building lot because of its natural amenities, planning and designing of all infrastructure for preserving the natural vegetation to take advantage of cooling and rainfall interception by trees, and building houses on piers or stemwalls instead of clearing and filling the entire lot.

While LID was embraced around the country and indeed around the world, it has been slow to come to Florida. Florida has been slower to embrace it for several reasons. First, we have very different physical conditions—rainfall, geology, hydrology including high water tables in some parts of the state—from many other areas, and we have five quasiindependent water management districts with different permitting requirements. The perception has been that while LID may work in Prince George’s County or Portland, Oregon, it will not work here because of our unique conditions. This issue of the Journal offers papers that demonstrate that Florida is now developing the research and practical knowledge to adapt LID techniques for Florida conditions so that design professionals and
regulators can feel confident that LID will work throughout Florida’s diverse meteorological and hydrogeological conditions. The second reason that LID has been slow to come to Florida is concern about ensuring the ongoing operation and maintenance of decentralized water management systems. We have spent the last century operating under the assumption that large, centralized water management facilities are cheaper, and more efficient to operate. This has certainly been true of efforts since the 1970s and 80s to decommission small, inefficient package wastewater treatment plants and replace them with large, centralized, municipally operated wastewater treatment facilities. This was at the heart of efforts to restore many estuaries around Florida by improving the level of wastewater treatment and reducing the volume of treated wastewater discharge to the estuaries.A previous issue of the Journal discussed the benefits of reusing reclaimed wastewater or stormwater to decrease these discharges.Now the challenge is to develop a new vision of efficiency. Perhaps measures of the efficiency of stormwater management efforts and facilities should involve a new concept of cost-benefit analysis that includes considering benefits such as groundwater recharge, maintenance of micro-climate, and the economic benefits of creating walkable communities. This latter concept is outside the realm of stormwater but within the realm of sustainable development which is the ultimate goal. These measures should also consider the benefits of a more natural hydrologic regime such as maintenance of minimum flows and levels and preservation of salinity regimes in Florida’s estuaries. The cost-benefit analysis should consider the benefits of cost avoidance by reducing pollutant loads at the source rather than conveying them downstream where Total Maximum Daily Loads (TMDLs) might require a regional stormwater treatment facility to reduce the excess loading to receiving water bodies.Additional cost-avoidance benefits may accrue due to the USEPA’s proposed numeric nutrient criteria for Florida. Implementing these criteria could impose significant costs to reduce pollutant loads if the volumes of runoff that result in increased loads do not simulate predevelopment volumes as is the goal of LID. The proposed State-wide Stormwater Rule may mandate post=pre development volumes and pollutant loads, thus further adding to the cost avoidance advantages of using an improved cost-benefit analysis.

Definitions of what constitutes LID may cause some confusion as we all become familiar with new concepts and techniques. For instance, Thomas Low in the Congress for New Urbanism Report, Light Imprint: Integrating Sustainability with New Urbanism, 2008, asserts that LID does not distinguish between developments of differing characters and goes on to state that stormwater treatment Best Management Practices focus on engineering rather than planning and design. His suggestion is that “Light Imprint” incorporates the planning and design considerations.

Yet the Florida Planning Toolbox, prepared by the Center for Urban and Environmental Studies of Florida Atlantic University for the Department of Community Affairs includes LID under the Water Resource Planning Tools. The Toolbox includes the following synopsis of the LID Development design features:

• Using green roofs.

• Using rain barrels and cisterns.

• Increasing the use of pervious surfaces and reducing or disconnecting impervious surfaces.

• Conserving natural systems or functions.

• Allowing on-lot micro-depressions or storage.

• Facilitating more compact, higher-density development to help preserve open space and reduce the amount of land disturbed for development.

During a recent 8-month stormwater study of River Forest, an LID development in Manatee County referenced in the Florida Planning Toolbox, the development never produced measurable runoff.

On the other hand, the proposed State-wide Stormwater Rule Applicants Handbook has incorporated LID techniques such as pervious paving, stormwater harvesting, and greenroofs with cisterns as individual BMPs and does not include them under the LID section.The LID section includes non-structural techniques, such as natural area conservation, Florida Friendly Landscaping, disconnecting impervious areas, reforestation, and rural subdivisions. Sarasota County has prepared a manual, targeting professions, entitled Sarasota County Low Impact Development Manual. The techniques covered in this manual include: Detention with Biofiltration, Shallow Bioretention, Pervious Pavements, Rainwater and Stormwater Harvesting, and Greenroof Stormwater Treatment Systems. Work is currently beginning to add the following techniques: vegetated filter strips, soil amendments, tree box filters, and enhancements to Chapter 2 which is “Evaluating Your Site and Planning For LID.”

History of Development Practices in Florida

The original Florida is chronicled in Michael Grunwald’s The Swamp 2005. He describes the attitudes in the mid 1800s about how flat, wet, swampy, hostile, and useless south Florida was 300 years after Europeans first set foot on Florida soils. It was in the mid 1800s that our water management and land development methods first evolved.These methods involved building drainage networks to quickly remove freshwater from where it fell as rainfall, was stored in wetlands, recharged groundwater, grew luxurious vegetation, and supported prolific wildlife. Dredges were brought in to begin digging canals that would drain huge amounts of freshwater from inland areas and discharge it into the prolific estuaries that lined Florida coastline. This was to “reclaim” the useless swamplands into productive agricultural lands that were extremely productive when using rich peat soils that had developed over thousands of years. It also provided flood protection that allowed areas that were previously considered uninhabitable to be settled. These methods have evolved today to our “conventional” development techniques.

Description of Conventional Development Techniques vs. LID

1. Conventional development techniques involve:

a. Clearing native vegetation, which results in microclimate effects due to loss of evapotranspiration and rainfall interception.

Rainfall interception by tree canopy can significantly affect the volume of water hitting the ground, particularly for small rainfall events. In some areas of Florida, small events make up the majority of the storms. In the Tampa area approximately 88% of the rainfall events are 1 inch or less. And in Jacksonville, Key West, Miami, and Orlando, the percentage is even greater.

(Harper, 2007) Thus, interception of rainfall in these areas can have a significant effect on the annual volume of runoff, particularly when the trees are in an area surrounded by Impervious surfaces.

B. Filling on top of native soils with resultant soil compaction and poor soil structure and quality results in greater use of water, fertilizer, and pesticides. Compacting the soil/fill either intentionally or inadvertently due to driving and parking of heavy equipment over these soils results in increased runoff even from “pervious” surfaces such as subdivision yards.Compaction during construction can reduce the infiltration rate of pervious areas to the effective equivalent of impervious surfaces (Gregory et al., 2006). This reduction in infiltration will potentially lead to an increase in the volume of runoff.

C. “Improving” the drainage and providing flood protection via dredging of canals and ditches, often in conjunction with the construction of impervious roads and parking lots with curb and gutter is designed to speed the delivery of stormwater into receiving waterbodies. This, along with the soil compaction discussed above and increased impervious surfaces that often accompany development, increases the volumes and changes the timing of freshwater discharged into lakes, rivers, and estuaries. This often results in the loss of available freshwater and changes the salinity in estuaries. It further reduces groundwater recharge, causes dewatering of wetlands, and eliminates water storage areas. Wetlands and natural depressions tended to store rainwater that fell on the land and allowed infiltration, evapotranspiration, and slow release of the freshwater to downstream receiving waterbodies.

D. The increase in volume of runoff that results from conventional development techniques requires larger conveyance systems and increases pollutant loads delivered to receiving waterbodies. LID’s potential lies in controlling pollutants at or near the source and in reducing the volume of runoff and, therefore, the pollutant load.

2. Low-Impact Development Techniques can:

a. Achieve water conservation - 99% of the water on earth is unavailable for human use. It is saltwater in the oceans (97%) or tied up in icecaps and glaciers (2%), which of late seems to be rapidly melting and mixing with seawater. Of the 1% available to human use, 99% is groundwater. LID can capture and store “run-in” in bioretention systems and cisterns or greenroofs.

B. Recharge groundwater- Recharging groundwater will become more and more critical as development continues and more impervious surfaces impede groundwater recharge.Maintaining that recharge will be critical to ensuring sustainable water supplies, maintaining baseflow in streams, and supporting natural wetlands and upland vegetation.Additionally, LID can provide alternative water supply directly via cisterns and stormwater harvesting.

C. Reduce stormwater runoff volume- Volume reduction is a critical component of pollutant-load reduction and restoration of the natural hydrologic regime. Increased volumes of freshwater have degraded estuarine habitats for fauna such as oysters and the nurseries for juvenile fin fish.

D. Preserve native soils and vegetation- Preserving native soils and vegetation is a basic tenet of LID and can provide carbon sequestration in trees and shading of sidewalks, roads, parking lots, and buildings. Less cooling requirements mean less energy use and less air and water pollutant loading.

E. Reduce energy consumption- Reduction in energy consumption due to reduced cooling costs, reduced pumping of ground and surface water, and reduced water treatment needs can be ancillary benefits of using LID practices. EPA’s Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices 2007, found that for every 10% increase in tree cover in water source areas, water treatment and chemical costs decreased by approximately 20%, up to about 60% tree cover.

F. Reduce construction costs- And last but not least, LID can reduce construction costs due to less paving, less volume of runoff to convey and resulting smaller conveyance systems, reduced landscaping needs, less land cost for stormwater treatment facilities by use of landscape areas, medians, buffers, etc for LID facilities. The comparison shown in Table 1 is taken from a USEPA document that shows that often the cost for LID development is less than for conventional development

g. Increased removal of pollutants with reduced cost. Each LID has a construction and operating cost. If volume reduction can be shown, then more than likely pollution mass will be reduced.
Thus, the benefit can be measured by the mass removed per dollar invested. What is needed are data on the pollution removal effectiveness. These papers within this issue provide some insight into effectiveness and cost.

Conclusion

LID is another tool in our stormwater/land planning tool box that can be used to help reverse a century’s worth of cumulative impacts that have increased the volumes and pollutant loads of stormwater runoff. However, LID is not a silver bullet. For new or greenfield development it can help mimic the natural hydrology of the site. As Florida gains more experience with these “new” techniques and gathers more data on their effectiveness, it’s likely that LID will emerge as the sustainable way to develop, redevelop, and retrofit. This may well show that LID can save money and at the same time support the New Urbanism concept of walkable communities with extensive use of street trees and bioretention areas in roadway and parking lot medians, which create “run-in” rather than “run-off.” FDEP recently stated at a public workshop on the Statewide Stormwater Rule that only about 50% of current stormwater systems are being maintained. Perhaps LID facilities that have aesthetic value, such as street trees, or that reduce the need to buy potable water for irrigation, toilet flushing, etc. will provide an inherent incentive to the owner/operator to properly maintain them.The articles which follow will help you understand how far Florida and the nation have come on the LID issue with respect to adapting LID techniques to work with Florida’s unique meteorology and hydrogeology.

References

• Center for Urban and Environmental Studies, Florida Atlantic University. 2007. The Florida Planning Toolbox, prepared for the Florida Department of Community Affairs.

• Coffman, Larry. 2000. Low-Impact Development Design Strategies, An Integrated Design Approach. EPA 841-B-00-003. Prince George’s County Maryland. Department of Environmental Resources, Programs and Planning Division.

• Gregory, J.H., M.D. Dukes, P.H. Jones and G.L. Miller. Effect of urban soil compaction on infiltration rate. Journal of Soil and Water Conservation May 2006 Vol. 61 no. 3117-124.

• Harper, H.H. and David M. Baker. 2007. “Evaluation of Current Stormwater Design Criteria within the State of Florida”. Final report submitted to Florida Department of Environmental Protection.

Tallahassee, Fl. Under Agreement S0108. This report can be downloaded from: http://www.dep.state.fl.us/water/nonpoint/pubs.htm#Urban_ Stormwater_BMP_Research_Reports

• Prince Georges’s County, Department of Environmental Resources.

1993. Design Manual for Use of Bioretention in Stormwater Management, Prince George’s County, Maryland. Department of Environmental Resources, Division of Environmental Management, Water Protection Branch.

• Rushton, Betty. 1999. Low Impact Parking Lot Design Reduces Runoff and Pollutant Loads. Annual Report #1. Aquarium Parking Lot, Tampa, Florida.

• Sarasota County, Environmental Services. 2009. Sarasota County Low Impact Development Manual.

• USGS Website Science for Schools.

Http://ga.water.usgs.gov/edu/earthwherewater.html

Read the full article at http://www.bluetoad.com/article/Low-Impact+Development+Comes+To+Florida/632175/60407/article.html.

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