Watershed-Scale Evaluation of Green Infrastructure Effectiveness at Reducing Runoff and Pollutant Loads

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1 Watershed-Scale Evaluation of Green Infrastructure Effectiveness at Reducing Runoff and Pollutant Loads Kate Meierdiercks Dept. of Environmental Studies and Sciences Siena College

2 Site-Scale Evaluation of GI Many sources out there summarize and synthesize the performance of GI projects. Show that effectiveness of GI is GI categorydependent Site-dependent Pollutant-dependent (Center for Watershed Protection (CWP) [2007], Koch et al. [2014], Leisenring et al. [2014])

3 Remaining Uncertainties Characterization of runoff and water quality from different urban land uses; Need for continued data collection for evaluation of GI systems over different spatial and temporal scales and climatic conditions; Need for assessing removal of emerging and difficult-tomeasure contaminants by GI practices; Enhancement of metrics and modeling techniques for evaluating the performance of GI practices; Scaling of the performance of GI practices from lot scales to watershed and regional scales; Development of easy-to-use decision support tools incorporating GI practices; and Need for addressing road blocks to increase GI adoption. Ahiablame, L. M., Engel, B. A., & Chaubey, I. (2012). Effectiveness of low impact development practices: literature review and suggestions for future research. Water, Air, & Soil Pollution, 223(7),

4 Watershed-scale GI evaluations Two approaches Monitor a watershed (collect water quality and quantity data in the field) Before and after watershed-wide GI implementation Paired watersheds Very few studies Use a rainfall-runoff model More studies use this approach Shuster et al. [2013]

5 Nearly Watershed-Scale The Jordan Cove Urban Watershed Project in Waterford, Connecticut Designed to monitor the effects of a traditional (17 lots) and GI (12 lots) subdivision (grassed swales, bioretention areas, pervious pavements). Traditional = large increases in runoff and pollutant export; GI = runoff depth and nitrogen/phosphorus export same as predevelopment. GI = longer lag times Dietz [2007], Dietz & Clausen [ 2008], Hood et al. [2007]

6 Approach 2: Rainfall-runoff model Several options: EPA Storm Water Management Model (SWMM) System for Urban Stormwater Treatment and Analysis INtegration (SUSTAIN) Model Long-Term Hydrologic Impact Assessment Low Impact Development (L-THIA- LID) Model

7 Watershed-scale modeling studies Unsurprisingly, like site-scale evaluations, results are GI category-dependent, site-dependent, pollutant-dependent But also scale-dependent, rain-dependent (volume and temporal variability) In general, results do indicate that GI reduces runoff and pollutant loads. However, literature reviews that synthesize this work are needed. Our work in the Kromma Kill Watershed (Albany County) is adding to this body of research

8 Kromma Kill Watershed Albany County NY Tributary to the Hudson 20 km 2 Community Scale Urban/Suburban,19% IMP Brownfield Site (heavy metals, PCBs) MS4 regulated municipalities NYS 303d impaired waterbody Siena cited as a source of flooding and water quality problems Upstream v. downstream No stormwater management plan (yet)

9 Flooding and Other Water Quality Issues in the Kromma Kill July 2011 April 2011 Photos courtesy of Peter Hess

10 GI Modeling in the Kromma Kill Kromma Kill subwatershed (213 acres) Use GIS to construct and parameterize model Use monitoring data collected in the field data as forcing, calibration, and validation Nick McCloskey ( 17) Examining the impact of Wetlands versus green roofs Centralized versus decentralized

11 Percent removal 0:01 0:11 0:21 0:31 0:41 0:51 1:01 1:11 1:21 1:31 1:41 1:51 2:01 2:11 2:21 2:31 2:41 2:51 3:01 3:11 3:21 3:31 3:41 3:51 4:01 4:11 4:21 4:31 4:41 4:51 5:01 5:11 5:21 5:31 5:41 5:51 6:01 6:11 6:21 6:31 6:41 6:51 Flow(CFS) Results Flow during design storm BAU (centralized wetland) Hours No Wetland (Control) Decentrlized Green Roofs Decentralized Wetlands Centralized Green Roof Percent removal of pollutants (conc.) TN TDS 20 NO BAU (centralized wetland) No wetland (control) Decentralized Green Roofs Modeled scenario Dentralized Wetlands Centralized Green Roof TP

12 Results Quantity Quality For the viable management scenarios wetlands reduce peak flow more effectively than green roofs, but green roofs more effectively reduce the runoff volume even though the green roofs treat a smaller drainage area. But is the difference due to centralized v decentralized or green roof v wetland? The centralized wetland reduces peak flows better than the centralized green roofs. However, the centralized green roofs reduce the runoff ratio. Suggests that wetlands are better at reducing peak flows, while green roofs reduce the runoff ratio regardless of centralized v decentralized The decentralized green roofs reduce peak flows and the runoff ratio better than decentralized wetlands. Decentralized GI only works if its detention rather than retention For the viable management scenarios green roofs removed all pollutants more evenly although the wetland removed some more efficiently (TP,NO3) but other less efficiently (TN, TDS). On average the best scenario for removing pollutants was the decentralized green roofs. Results depend on whether you re interested in peak flows or volumes and the type of contaminant. The centralized wetland does the best job at reducing peak flows, but decentralized green roofs reduce the greatest volume of runoff. Decentralized green roofs remove the most pollutants overall. Centralized Wetlands remove TP and nitrates very efficiently however they don t remove TN or TDS well. Centralized green roofs treat all pollutants very poorly but are similar to wetlands in their ability to remove TN and TDS Centralized wetlands are better but are limited by natural processes, while centralized green roofs are limited by their intended purpose (detention). The decentralized green roofs severely out compete decentralized wetlands in pollutant removal. Decentralized GI works more efficiently if it is based on detention. Viable management scenarios = decentralized green roofs and centralized wetlands Centralized green roof and decentralized wetlands were examined as a thought experiment and to see whether differences we observed in the viable management scenarios were due to GI type or location.

13 Continue Kromma Kill SWMM modeling GI modeling in Patroon Creek Watershed (itree Hydro, EPA BMP siting tool) Next Steps

14 Concluding Remarks Results from site-scale and watershed-scale GI studies are variable. Even though more synthesis is needed for the watershed-scale studies, in general, GI has been shown to reduce runoff and pollutant loads. Results from the Kromma Kill Watershed suggest that GI is not a one size fits all solution. The most effective GI type and location depends on the management objective. How do we determine what is most important for our watershed? Through field studies, landscape analyses, and modeling. Take home message: Be sure to think about water problems at the watershed scale. Even though urban watersheds are complex, get to know your watershed through field data collection, landscape analyses, and modeling studies. Even though there is uncertainty associated with any watershed study (or studies), basing management decisions on these studies is better, in my opinion, than nonevidence-based management decisions.

15 Thank you Dr. Mary Beth Kolozsvary Dr. Kevin Rhoads Dr. Jean Mangun Michele Golden ( 14) Nick McCloskey ( 17) CONTACT: kmeierdiercks@siena.edu Bit.ly/kmeierdiercks