Bridget M. Wadzuk

Fines accumulation and distribution in a storm-water rain garden nine years postconstruction.

Storm water control measures (SCMs), also known as best management practices (BMPs), such as rain gardens, are designed to infiltrate storm-water runoff and reduce pollutant transport to surface waters. The life span of these SCMs may be limited depending on the composition of sediments in runoff water. Settling of fine sediments may clog soil pore spaces, reducing the infiltration capacity of the soil and reducing the potential benefits of this SCM. A study was conducted on a Villanova campus rain garden that accepts runoff from an adjacent parking lot to determine if there was a relationship between the accumulation of fine sediments over time and the infiltration capacity. The soil textural profile within the rain garden was characterized prior to SCM installation (2001), after installation, after five years, and after seven years of receiving storm-water runoff. Infiltration data were collected by the single-ring infiltrometer method in 2006 and 2009. Differences in soil texture were found between loc...

Understanding the Role of Evapotranspiration in Bioretention: Mesocosm Study

AbstractMany regions are turning toward sustainable green infrastructure practices, such as bioretention to mitigate urban stormwater runoff. Currently, the designed volume control in bioretention stormwater control measures (SCMs) is attributed to infiltration, although evapotranspiration (ET) can be considered a viable mechanism. From a water cycle perspective, reduced ET in urban spaces is a primary source of the increased stormwater runoff volume. This research demonstrates that ET is a substantial water balance component of two differently configured bioretention mesocosm systems. Over a two-year span of time, a freely draining bioretention mesocosm (lysimeter) converted 50% of the direct rain falling on the mesocosm to ET, contrasted by a bioretention mesocosm (lysimeter) with an internal water storage (IWS) layer that converted 78% of the direct rainfall to ET. The measured daily average ET was 6.1  mm/d for the IWS lysimeter and 3.1  mm/d for the freely draining lysimeter from April to November in...

Parking Deck's First Flush

The goals of storm-water management have shifted from a flood control to a holistic and sustainable strategy, emphasizing the relationship between rainfall event size and pollutant loadings. The first flush concept is the first part of a rainfall event that contains the largest pollutant loading. Questions have been raised on the concepts validity for storms across different land uses and pollutant types. The existence and magnitude of the first flush impacts sizing of best management practices used to meet pollutant reduction goals, assessment sampling methodologies, and state storm-water management strategies. Current concepts support the use of distributed control measures focused on smaller storms off impervious surfaces. Runoff from a small impervious parking area was sampled incrementally during multiple storm events to measure pollutant concentration with respect to storm depth. This sampling routine established the existence of a first flush for a single use paved parking area. Total suspended solids, nitrate, chloride, dissolved copper, and dissolved cadmium exhibited a first flush up to a rainfall depth of 25.4 mm; total dissolved solids, total nitrogen, total phosphorus, nitrite, phosphate, and dissolved chromium did not exhibit a first flush.

The effect of field conditions on low Reynolds number flow in a wetland.

Stormwater runoff has been an environmental concern since the 1980s. Green infrastructure, such as constructed stormwater wetlands (CSWs), is a tool in stormwater management, however, little is known about the hydraulic diffusion processes that impact water quality in low flow, laminar (i.e. baseflow) conditions. Diffusion provides the mechanisms that distribute and mix water through a CSW and therefore how pollutants will be spread through the CSW impacting the water quality. Laboratory experiments were performed by Nepf, H.M., Sullivan, J.A., Zavistoski, R.A. [1997. A model for diffusion within emergent vegetation. Limnology and Oceanography, 42(8), 1735-1745], and Serra, T., Fernando, H.J.S., Rodriquez, R.V. [2004. Effects of emergent vegetation on lateral diffusion in wetland. Water Research, 38(1), 139-147] to examine the effect of plant density on diffusion in laminar flow conditions. Nepf, H.M. [1999. Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research, 35(2), 479-489] proposed a model predicting the diffusion coefficient based upon the plant density for both laminar and turbulent flow conditions. The present study examines the effect of field conditions on diffusion in a laminar flow field and verifies the diffusion model created by Nepf, H.M. [1999. Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research, 35(2), 479-489]. The results from the present study show that the laminar flow model, based solely on mechanical diffusion, is not sufficient for field conditions and the total diffusion model must be used. The variability in flow conditions and stem diameter found in the field produce pockets of turbulence and dead zones that must be considered to predict the diffusion coefficients in low flow CSWs. A sensitivity analysis of the dead zone term shows that the laboratory, field and diffusion models lie within an acceptable theoretical range for the observed or predicted diffusion coefficient. In addition, a model was created using the Danish Hydraulic Institutes Mike 21 software. Model results indicate that non-uniform velocities significantly affect the diffusion coefficient and a range of diffusion coefficients should be considered when designing CSWs.

Evapotranspiration in Rain Gardens Using Weighing Lysimeters

AbstractQuantification of evapotranspiration (ET) and infiltration from vegetated stormwater control measures (SCMs), such as rain gardens, is necessary to properly assess their volume reduction po...

Evapotranspiration and Infiltration in Rain Garden Systems

Quantification of evapotranspiration (ET) and infiltration from vegetated stormwater control measures (SCMs), such as rain gardens, is necessary to properly assess their volume reduction potential. Weighing lysimeters at Villanova University mimic three bioretention rain garden designs and measure water budget parameters to determine how design elements impact ET and infiltration (percolation). The designs compare two soil medias: a loamy sand (72% sand, 12% silt, 1% clay) and sand (96% sand, 4% silt, 0% clay), and different drainage systems: a controlled valve and internal water storage (IWS) outflow. The controlled valve outflow allows a user defined flow rate. The IWS outflow maintains a storage volume within the media. A custom distribution system was built to simulate excess rain delivered to a rain garden during natural storm events. In Pennsylvania, SCMs are often sized to control a multiple (typically 5:1 for rain gardens) of a selected rain event. Trials were performed in April and August 2014 for half open controlled valve configurations. Both loamy sand and sand soils with a controlled valve configuration showed an average ET of 3.1 mm per day for 7 days after simulated 5:1 events. Sand soil with an IWS showed an average of 6.0 mm per day for 7 days after simulated 5:1 events. Simulated storm events produced larger ET rates, on average, than that of a 1:1 ratio. Comparisons of predictive equations show the ASCE Penman-Monteith (uncorrected for water stress or crop type) under-predicting and Hargreaves (corrected for water availability) over-predicting observed ET, but follows the trend of each lysimeter.

Evaluating the Role of Evapotranspiration in the Hydrology of a Bioinfiltration Basin Using a Weighing Lysimeter

Bioinfiltration basins require substantial land area in order to reduce peak outflows and improve the water quality of stormwater runoff. An increased understanding of the water budgets occurring within these basins could result in more efficient land usage. For example, the role of water losses through groundwater recharge, and specifically evapotranspiration (ET), are not well understood. However, research on the entire water budget may yield design standards resulting in substantial volume reduction in bioinfiltration basins when the contribution of ET is viewed through an appropriate time horizon. In order to measure the ET and groundwater recharge occurring in a bioinfiltration basin, a weighing lysimeter was designed and constructed. Storms were simulated representing varying field conditions. These simulations mimicked two and a half hour storm events of 13, 19, and 25 mm producing runoff occurring from both 5:1 and 10:1 impervious area to lysimeter area loading ratios. The simulations were conducted during the morning and evening and in different seasons. Results indicate that the ET measured 24 hours after the storm simulation was found to range from 2.6 to 31.4 mm of water. The measured ET was found to be strongly correlated (R 2 = 0.63) to the climatological parameters that govern the Penman-Monteith equation. The measured ET was compared to the Penman-Monteith reference ET 0 and a mean crop coefficient (K c ) of 1.85 was determined for the summer months. The measured ET was also found to be dependent on the soil saturation of the lysimeter prior to the storm simulation. A soil-water characteristic curve was developed for the soil in the lysimeter. It was determined that the greater the soil suction throughout the storm simulation, the more water that was available for ET, and ET increased relative to groundwater recharge.

Green Infrastructure Recovery: Analysis of the Influence of Back-to-Back Rainfall Events

AbstractA core concept in stormwater green infrastructure (GI) design is whether a system will meet its rainfall-runoff volume capture goals within a period of time after a previous event. In GI de...

How Students Spend Their Time

AbstractAn analysis was performed of how students spend their time while pursuing a bachelor of science in civil engineering at Villanova University. The purpose of this study was to determine how many hours per week students spent both in and out of class and how the students spent their time when not in class or studying. Another purpose of this study was to provide a methodology for tracking how much time students spend on their course work that could be applied at other universities to monitor academic stress and rigor. Several data sources were used to gather data on how the students were spending their time: Higher Education Research Institute (HERI) surveys, end-of-semester course surveys, the recommended curriculum for each semester, and time logs. Overall, the data indicate that the amount of time students devote to their course work has fluctuated throughout the years. In six out of the eight semesters that students are in the program, they were found to study more often in 2011 than they did in...

An Extremely Undersized Infiltration Trench 10 Years Later

Infiltration trenches are a stormwater control measure (SCM) used in urban and ultraurban areas to provide stormwater runoff volume reduction. Legacy infiltration trenches are difficult if not impossible to maintain and were often built without pretreatment. As runoff with high suspended solid loads enters an infiltration trench there is continual buildup of solids that clog the infiltrating surface, decreasing the hydraulic conductivity at the soil interface and the performance and longevity of these systems. The present study builds on previous work at Villanova University on an extremely undersized infiltration trench (directly connected impervious drainage area to SCM area of 160:1) to artificially accelerate annual loading to evaluate long-term performance. Ten years and 1270 cm of rain later, infiltration through the bottom of the trench has nearly ceased and the sides have slowed as well. Recession rates have reached an equilibrium point where they no longer improve or decrease.