RAINWATER HARVESTING: A SUSTAINABLE SOLUTION TO STORMWATER MANAGEMENT
In most urban areas, conventional stormwater management has led to increasing environmental and economical problems. It is becoming increasingly important to better utilize the limited amount of available water resources as global population growth and climate change are forecasted to increase water stresses such as flooding and drought. Locally in the Borough of State College and at the University Park Campus of The Pennsylvania State University (Penn State), stormwater flooding has caused infrastructure damage and environmental ecosystem damage in terms of erosion, sedimentation, flooding and potential pollution. Stormwater can be viewed either as an expensive threat to environmental protection and social wellbeing, or it can be viewed as an opportunity to promote micro-watershed sustainable development through the use of decentralized stormwater solutions such as rainwater harvesting (RWH).
The overall goal of this thesis is to demonstrate how RWH is a sustainable solution to stormwater management. Therefore, a study was conducted to investigate whether RWH could mitigate future climate change effects on stormwater runoff and help restore natural pre-development stormwater flow patterns, hence improving stormwater quantity and quality before the runoff enters receiving waters. RWH also was tested to determine whether it was a financially feasible answer to stormwater management.
In order to conduct an urban stormwater impact assessment, hydrologic discharge data were collected from an outlet storm-sewer in the East Campus Drainage Area (ECDA) at Penn State and used to calibrate the Storm Water Management Model (SWMM). Also, a financial comparison between a RWH system and the implementation of a green roof on a building under construction at the university with a conventional subterranean stormwater facility was assessed. Through the simulation of five storm events, the ECDA-SWMM hydrologic results indicate that RWH at Penn State has the ability to decrease stormwater quantity peak runoff by 52.7% and total volume runoff by 46.1%. This resulted in a potential decrease of possible future flooding events, a decrease of potential constituents of water quality pollution, and assisted in water conservation. Results from the financial analysis indicate that Penn State could realize savings of between $10 million to $30 million over the next 30 years by investing in RWH in future buildings instead of green roofs and conventional stormwater management facilities.
TABLE OF CONTENTS
Conventional stormwater management relies on expensive and centralized infrastructure systems, such as large, expensive stormwater pipes and detention ponds that concentrate and transport rainfall (and potential pollutants) to receiving bodies of water. For example, at The Pennsylvania State University, University Park campus (Penn State) and in the Borough of State College (SCB), stormwater is managed through pipes and ponds, which may result in environmental degradation to receiving waters because of the increased peak and total volume runoff which erodes stream banks, introduces contaminants, and increases the water temperature (CC, 2007). In some areas of the SCB, peak stormwater flow and total runoff volume currently exceed piping capacity resulting in infrastructure property damage (Hopkins, 2002; Smeltz, 2005). Increasing pipe size to mitigate this problem is expensive and only exacerbates downstream ecosystem damage. According to the U.S. Environmental Protection Agency (EPA) and the Intergovernmental Panel on Climate Change (IPCC), the frequency of high intensity rainfall events leading to flooding can be expected to increase in the future because of climate change(CIER 2008; UCS, 2008). This will result in greater runoff to receiving waters and less infiltration for aquifer recharge if not addressed by proper management. Hence, there is an urgent need to take a more holistic and sustainable approach to the management of stormwater runoff.
This thesis seeks to determine whether stormwater runoff, when managed sustainably through rainwater harvesting (RWH), can become a valuable resource and not a financial and environmental liability. The sustainable management of stormwater requires a different approach from the conventional conveyance and disposal paradigm. It is proposed here that if stormwater is treated as a resource, and managed through the use of properly engineered decentralized stormwater harvesting systems, the resulting benefits will be multiple: decreased stormwater runoff peak and volume with the associated environmental impact and reduced demand for potable water. Stormwater harvesting can be a key to sustainable water resource management as it reduces aquifer depletion, potable water costs, non-point pollutant discharge, and future flooding events that could potentially cause infrastructure damage. Using the East Campus Drainage Area (ECDA) at Penn State as a case study, the potential for RWH will be evaluated from both engineering and economic perspectives.
This thesis is organized around the following specific goals:
- Define sustainability and its role in stormwater management in the 21st
- Discuss global sustainability in terms of water and wastewater
- Review the literature of the progression of stormwater management throughout time
- Discuss economic instruments for stormwater policies
- Review the literature of state-of-the-art rainwater harvesting technology. Explain how reusing stormwater benefits the following:
- Stormwater flooding concerns
- Water quality issues
- Water conservation concerns
- Project future increases in severe precipitation events.
- Discuss the science of climate change and its relationship with the hydrological cycle
- Summarize future climate change effects on precipitation in the Northeastern
USA, the Mid-Atlantic region, and Pennsylvania
- Discuss the potential problems facing local stormwater infrastructure because of future climate change scenarios
- Collect runoff discharge data from the ECDA on the Main Campus Basin and use these data to calibrate a numerical model for decision-making.
- Develop a computer-based modeling tool that can produce good estimates of the rainfall/runoff observed storm events
- Run a sensitivity analysis with the ECDA model to identify important parameters for the model calibration
- Explain limitations of the ECDA model simulations
- Using building roof area data, calculate the volume potential of harvested rainwater for Penn State given current average rainfall rate (i.e., 100% RWH potential).
- Analyze the harvesting potential by implementing the RWH scenario through diversions on building rooftops within the ECDA model
- Evaluate the hydraulic and hydrological effects that RWH would have on the
- Discuss how RWH can mimic nature by running the ECDA model in a predeveloped scenario
- Determine the monetary value of harvested rainwater.
- Discuss the potential water savings from collecting and reusing stormwater in
- Perform a financial analysis of the benefits if Penn State implemented RWH in new building infrastructure
- Predict future stormwater regulations and the attendant economic benefits of RWH if implemented in certain scenarios
RAINWATER HARVESTING: A SUSTAINABLE SOLUTION TO STORMWATER MANAGEMENT