Dissertation

Resilience of Green Infrastructure under Extreme Conditions

Winston, Ryan Joseph

2015

Overview

Green infrastructure improves urban runoff quality and controls runoff volume by maximizing exfiltration, evapotranspiration (ET), storage, and water harvesting. To determine their resilience to various factors (e.g., clay soils which restrict exfiltration, climate change, and application of de-icing salts), three bioretention cells and four permeable pavements were intensively monitored in northern Ohio. To ensure resilience over the longterm, permeable pavements were evaluated to determine (1) when maintenance is needed and (2) how to best maintain the pavement surface infiltration rate (SIR). Volume reduction for bioretention cells constructed over low permeability soils varied from 36-59% and improved with higher drawdown (i.e., the sum of exfiltration and ET) rates and deeper internal water storage (IWS) zone depths. Post-construction measured drawdown rates were non-linear and greater than vertical saturated hydraulic conductivity (Ksat) measured on the underlying soil during construction. Collectively, this suggested (1) lateral exfiltration played a substantial role in volume reduction, and (2) ET provided a minor amount of volume reduction. Field-collected bioretention hydrologic data were used to calibrate and validate DRAINMOD, a long-term agricultural drainage model. Nash-Sutcliffe efficiencies for runoff, drainage, overflow, and exfiltration/ET exceeded 0.7, suggesting the model was well calibrated. Analyses of bioretention design alternatives were conducted using the calibrated models and a long-term climatic record. Volume reduction was most dependent on loading ratio, IWS zone depth, and underlying soil Ksat. A current and two predicted mid-21st century climate scenarios (RCP 4.5 and RCP 8.5) were input into the three calibrated DRAINMOD models. Future climate scenarios predicted decreases in annual precipitation, longer dry periods, and hotter temperatures for Northeast Ohio. Bioretention volume reduction was predicted to either modestly increase (by 4-6%) or decrease (by 5-9%) under future climate scenarios. In all modeled cases, overflow and ET increased as a percentage of the water balance. To mitigate future increases in overflow, bowl volume would need to be increased by up to 51%. Field-monitored permeable pavements situated over low permeability soils, employing 15-cm IWS zones, and minimum loading ratios of 4:1 reduced runoff volume by16 to 53%. In comparison, volume reduction for a permeable pavement treating only direct rainfall was 99%. Post-construction drawdown rates were linear and similar to vertical Ksat of the underlying soil measured during construction, suggesting evaporation and lateral exfiltration were minor contributors to volume reduction. The water quality performance of two permeable pavements was assessed in northeast Ohio. While observed nutrient load reductions were similar to past studies, TSS loads increased by 300-500%. Loss of silt and clay-sized particles from the permeable pavement subgrade was seasonal, and appeared to be related to dispersion of particulate matter caused by sodium in de-icing salts. Eight maintenance techniques were tested for improvement of permeable pavement SIR in North Carolina, Ohio, and Sweden. Milling and pressure washing were the most successful in recovering porous asphalt SIR, while street sweepers employing suction were preferable for permeable interlocking concrete pavements. A simple infiltration test (SIT) to determine permeable pavement maintenance needs was developed because American Society for Testing and Materials (ASTM) tests can take hours to complete and require infiltrometers not readily available to maintenance contractors. Results showed: (1) a segmented linear relationship related SIT and ASTM-measured SIRs, (2) the SIT and ASTM tests predicted approximately the same IR up to 250 mm/min, and (3) the larger surface area of the SIT reduced measurement variability by 40% compared to the ASTM method. Bioretention cells and permeable pavements are resilient stormwater controls only when properly designed, installed, and maintained. Generally, bioretention cells are more resilient to anthropogenic and natural stressors due to their plant- and soil-based treatment processes.

• Publisher: ProQuest Dissertations & Theses
• Subject: Civil engineering / Water Resource Management / Water Resources Management
• ISBN: 9781369639490, 136963949X