Hydrologic modeling could direct eco-friendly urban, rural land development

Jaehak JeongDr. Jaehak Jeong sees the effects development has on the Lampasas River watershed every time it rains and water streams toward storm drains.

Jeong, a Texas A&M AgriLife Research associate professor, develops hydrologic models at the Texas A&M AgriLife Research and Extension Center in Temple.  He said he hopes the Soil and Water Assessment Tool, or SWAT, will change the way land is developed and help return developed land to its natural hydrologic state. Conceptually, SWAT could help prevent flash flooding, erosion, sedimentation and improve water quality.

SWAT is a river basin or watershed-scale model developed to quantify and predict various impacts development and land management practices have on water, sediment and contamination flow within large, complex watersheds with varying soil types, land uses and management conditions over long periods of time, Jeong said.

Jeong said simulation modeling is a useful tool for developers, city planners and landscape architects who are interested in how pavement, concrete, curb and gutter and rooftops can change the land’s hydrology. But simulations can be applied to any changes within a watershed, including agricultural activities such as row cropping and logging.

“We’re focused on providing a modeling tool that provides various options to decrease the negative effects development has on a watershed,” he said. “There is no single answer. Every watershed is different and faces different challenges. SWAT modeling can address them all under various conditions and how they may change over time.”

The modeling is made possible by layering Geographic Information System maps, including topographical, land-use and soil property maps, Jeong said. The model then simulates daily, hourly or minute-by-minute rainfall-runoff processes to determine the hydrological properties of the simulation area.

“We can read the topography to determine elevation changes and whether the land is urban, agricultural, forest or rangeland, and whether the soil is clayey, like Houston Black, or sandy and the pH balance and other properties that might affect soil hydrology,” Jeong said. “Then we can simulate a rain event, such as a half-inch rain over 20 minutes, to estimate runoff versus infiltration or vegetation uptake.”

SWAT modeling could help city planners and developers implement features that help return watersheds to more natural hydrologic states. Two benefits of improving watershed hydrology are reduced flash flooding and better water quality. (Texas A&M AgriLife Extension Service photo by Steve Byrns)

SWAT modeling could help city planners and developers implement features that help return watersheds to more natural hydrologic states. Two benefits of improving watershed hydrology are reduced flash flooding and better water quality. (Texas A&M AgriLife Extension Service photo by Steve Byrns)

The model can also estimate how much contamination, including pesticide, nutrient or phosphorous content, make it to nearby water bodies based on inputted activities such as pesticide applications in a cornfield or residents fertilizing lawns, Jeong said. The plant-growth model for vegetation can estimate how much of any specific application that goes into the soil could be washed out in runoff or stay for plants.

Simulations can even factor in potential management practices such as scheduled street sweeping that removes trash, sediments and other potential contaminants from urban pavements, he said.

“All activities in complex agricultural, urban or rural and forest watersheds can be simulated,” Jeong said.

In urban catchments, the simulation model can also show how stormwater management options, or “scenarios,” such as sand filters, retention/irrigation basins, porous pavement and rain gardens, can help return developed land closer to its natural hydrological balance, he said. Landscape architects can improve the hydrologic balance of watersheds by placing scenarios strategically throughout the area to aid absorption, slow or stop runoff and filter contaminants.

Jeong said city planners and officials are looking at the implications of development and urban sprawl 30-50 years into the future with SWAT modeling.

“They understand the impact of urbanization and so they are looking to set ordinances to minimize the effects of development on the city, its residents and the environment,” he said.

Jeong said there is excitement among landscape architects, engineers and other professionals who are interested in designing ecologically friendly concepts that could be beneficial to a watershed’s hydrology, including flood control and water quality management.

Dr. Roger Glick, city of Austin Watershed Protection Department manager, said the city of Austin is preparing a cost-benefit analysis of implementing scenarios in highly urbanized areas of the city to see how they perform.

“My gut tells me that our analysis will show there are many benefits of implementing various options to restore watersheds throughout Austin to as natural a state as possible and that modeling simulations will be a great tool that will assist the city regarding regulations related to stormwater management and water quality and how industry professionals develop land in the future,” he said.

Glick said implementing various scenarios in neighborhoods within the watershed would require buy-in from the public and elected officials, but he is optimistic that all stakeholders involved will realize the long-term benefits of introducing ecologically beneficial designs prescribed by SWAT models.

He said the city must determine how it would approach public-private partnerships with landowners and other stakeholders, such as providing incentives, before moving forward.

Jessica Wilson, education manager for Austin’s Watershed Protection Department, said the results of the analysis and budget discussions by city officials in 2018 will determine whether the city moves forward with a five-year pilot project that would feature scenarios within a 1.08 square mile section in an upstream portion of the Waller Creek watershed.

Wilson said the area is near downtown and highly urbanized. Around 40 percent of the project area is residential land use, so partnering with landowners will be a major consideration for the pilot program.

The area was also chosen because watershed monitoring gauges have been in place and historical data is available for comparison, she said.

She said the idea of introducing ecologically friendly options to slow water flows and filter contaminants is already being discussed among homeowner groups and non-profits. A neighborhood group within the watershed has applied with the city to remove pavement in a dead-end street near a school park and replace it with a rain garden.

Wilson said the residents see the project as a chance to expand the park in an environmentally friendly way.

The goal for the pilot project is to get 20 percent of landowners within the watershed to participate, she said.

“The idea is percolating through the area,” she said. “I think one thing that all the stakeholders have to realize is that many of their ideas for how to improve the watershed and the environment in their areas are not mutually exclusive and can complement each other.”

Wilson said there is no way to implement one option to improve existing watershed problems in such a highly urbanized area that would be feasible economically or politically. But the city and its dwellers can improve water quality and reduce flash flooding by applying various options according to SWAT models via public-private cooperation.

Jeong has proposals pending with other municipalities, including the city of Baltimore, which is looking to source data to determine nitrogen yields flowing into the Chesapeake Bay. Other countries, including Japan, are also utilizing SWAT modeling in various urban and agricultural applications.

He said momentum behind the simulation program is slowly building but that he expects interest could rapidly increase as concerns regarding detrimental effects of development on water quality and flooding mount.

“It’s on a natural pathway toward this tool being exposed to professionals,” he said. “Once landscape architects, engineers and city planners see the design benefits, I believe it will become a standard tool for sustainable urban and rural development in the future.”

By Adam Russell | AgriLife Today

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