Unit 2.2: Mitigation Using Low Impact Development (LID) Controls
In this activity, students model the impact of changes in land cover on stormwater runoff using the EPA's National Stormwater Calculator. Students mitigate increased stormwater runoff resulting from development with low impact development (LID) controls. Students assess the LID controls in terms of the ecosystem services that they are intended to replace and discuss alternative development designs to reduce the need for them.
Overall learning objective for this activity: Students will be able to assess the effectiveness of low impact development (LID) controls on the hydrologic impacts associated with land-use change.
Specific learning objectives for this activity:
- Students will be able to use the EPA's National Stormwater Calculator to model ways to mitigate the impact of development on stormwater runoff.
- Students will be able to incorporate LID controls into simulations of hydrology relative to expansion of a residential neighborhood.
- Students will be able to characterize the ecosystem services replaced by LID controls.
Context for Use
This activity is designed to be used in conjunction with the Unit 2.1 activity introducing the National Stormwater Calculator. This activity would be appropriate in a range of introductory courses in water resources, sustainability, ecology, environmental science, Earth science and geology, land use planning, anthropology, and landscape design.
Class Size: This activity can be adapted for a variety of class sizes.
Class Format: This activity is designed for individual lecture sessions, but it is suitable for use in a lab setting or as a homework assignment as well. Students can work together, in groups of 2–4, but each student should complete his/her own assignment.
Time Required: This activity is designed to be completed in a 50-minute class period.
Special Equipment: Student groups should have a computer running Windows that has access to the Internet. The Calculator, which runs only on Windows, must be installed from the Internet. The link is provided in the References and Resources section below. Because the Calculator downloads soils data from a national database, internet access is required during this activity. Not every student needs a computer for this activity, but at least one computer must be available per group. From the instructors' experiences, having at least one computer per three students is ideal.
Skills or concepts that students should have already mastered before encountering the activity: This activity assumes familiarity with basic concepts of ecosystem services and the hydrologic cycle.
Description and Teaching Materials
It is assumed that the Calculator has been downloaded and installed on the instructor's computer and on a computer available to each student group. Students will need to have completed the Unit 2.1 Tutorial (Microsoft Word 2007 (.docx) 5.6MB Dec1 16) for the pre-expansion (or baseline) data. Students will follow the Unit 2.2 Tutorial (Microsoft Word 2007 (.docx) 492kB Dec2 16) to model the impact of a proposed expansion of a residential neighborhood on stormwater runoff using LID controls to mitigate increases from pre-expansion levels.
If students have completed the Unit 2.1 Tutorial and Assessment, they will have previously saved a location file called Thomaston Trails Expansion Baseline.swc. Instructions in the Unit 2.2 Tutorial and Assessment will guide them using this file as the starting point. Following completion of the tutorial, students will answer a series of questions in the Unit 2.2 Assessment (Microsoft Word 2007 (.docx) 21kB Sep4 16) pertaining to their model results.
Teaching Notes and Tips
Review Answers for Question 7 from the Assigned Questions from Previous Session (5-10 min)
The connection between ecosystem services from Unit 1 and runoff modeled using the Calculator should be made explicit before moving on. You can do this by generating class discussion around question 7 from the assigned homework Unit 2.1 Assessment (Microsoft Word 2007 (.docx) 16kB Sep4 16).
Question 7: How are these impacts on the hydrologic cycle affecting the ecosystem services (Unit 1.1) provided by the forest cover?
Potential Answer: Forests and forest soils (any permeable surface, for that matter) absorb rainfall. By decreasing runoff, they reduce downstream erosion and flooding while recharging groundwater, which results in sustained baseflow of streams. Any of the following ecosystem services from the Ecosystem Services Fact Sheet (from the Ecological Society of America) is arguably impacted:
- moderate weather extremes and their impacts (indirectly)
- mitigate drought and floods (directly)
- cycle and move nutrients (directly and indirectly)
- protect stream and river channels and coastal shores from erosion (directly)
- detoxify and decompose wastes (directly and indirectly)
- generate and preserve soils and renew their fertility (directly)
- contribute to climate stability (indirectly)
- purify the air and water (directly and indirectly)
- pollinate crops and natural vegetation (indirectly)
as a direct result of infiltration of rainfall by the forest/permeable soil (e.g., infiltrated water does not contribute to flooding, but does recharge groundwater that increases resilience against drought)
indirectly resulting from infiltration of rainfall by the forest/permeable soil (e.g., increased soil moisture maintains dense plant growth that consumes, maintains, or stabilizes CO2)
Think-Pair-Share (5-10 min)
Begin with a think-pair-share exercise relative to the local campus and the general awareness of the students regarding issues like stormwater runoff, which are normally in the background (learn more about think-pair-share). Built environment, with impermeable surfaces, characterizes most campuses. Ask students to consider their local campus environment. Pose a rhetorical question: Has our campus impacted the hydrologic cycle? Based on the results from the previous class, the answer should be a resounding yes. If it is not, explore this through discussion. Impermeable surfaces negate the possibility of infiltration by the site's original soil.
Think-Pair-Share: What has the campus done to manage stormwater?
Answers may vary from no real recognition of how stormwater is removed from campus to either traditional or green methods for dealing with stormwater.
Traditional methods: catch basins, combined sewers, curbs and gutters, culverts, detention basins, lined storm channels, retention basins, roof downspouts, storm drains and pipe network, tiles
Green infrastructure, LID controls, environmental site design: bioretention cells, curb and gutter elimination, grassed swales, green parking design, infiltration trenches, inlet protection devices, permeable pavement, permeable pavers, rain barrels and cisterns, rain gardens, riparian buffers, sand and organic filters, soil amendments, stormwater planters, tree box filters, vegetated filter strips, vegetated roofs
You may also choose to use this as a unit wrapper around Unit 2 as described in the assessment section of the unit page. If so, you should ask students to write down their response in the "think" part of this exercise and collect their responses. Then finish the think-pair-share in discussion format. This should transition to LID controls on stormwater.
Introduce LID Controls in the National Stormwater Calculator (10 min)
Alternatively, as a pre-class assignment, you can have the students watch the first 20 - 25 minutes of the YouTube video "Green Technology Webinar Series - Stormwater Management: Low Impact Development and Greening Corporate Grounds."
Most new development should have minimal hydrologic impact going forward, so your introduction should refer to the utility of the Calculator for analyzing changes in hydrology at the screening or planning level. The effectiveness of LID controls can be evaluated by iterating through simulations and examining results. At this point, a simple understanding of the LID controls available in the Calculator will suffice; later, students will be asked to be more critical in their selection of LID controls.
Use of the National Stormwater Calculator (20 min)
Assign the Unit 2.2 Tutorial (Microsoft Word 2007 (.docx) 492kB Dec2 16). Remind students of the problem they worked on during the previous meeting or for homework. The goal here is to reduce the hydrologic impact of the proposed land use change to zero using LID controls. In other words, with the change in land cover to support the expansion, stormwater runoff will not increase over the amount prior to expansion, the baseline result from Unit 2.1 Tutorial and Assessment. This may take several iterations, but encourage students to understand the controls and not to use them carte blanche. There are costs associated with installation and maintenance that will be borne by the homeowners, so there is an economic incentive to optimize the use of LID controls.
Leave students with a parting question: In planning the development of the expansion area, can you do so in such a way as to optimize natural ecosystem services to reduce the need for and cost of LID controls?
Students have used the calculator to model the impact of LID controls for mitigating stormwater runoff. Their ability to analyze the results, and their understanding of the implications relative to LID controls and the ecosystem services that they are replacing are assessed based on their answers to the questions assigned in Unit 2.2 Assessment (Microsoft Word 2007 (.docx) 21kB Sep4 16). Answers can be turned in for grading or simply checked for completeness. Student answers can be the basis for class discussion in the next unit to evaluate student learning. A key is included:
References and Resources
National Stormwater Calculator User's Guide Version 1.1
Description and download page for National Stormwater Calculator
Green Technology Webinar Series — Stormwater Management: Low Impact Development and Greening Corporate Grounds