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HARVESTING STORM WATER SUSTAINABLE SOLUTION FOR RAINWATER MANAGEMENT

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12-September-2018

ABSTRACT:- Most of the areas like the urban areas; storm water management has led to the problems related to the economical and environmental to be increasing each and every day. It is now very important to utilize the better amount of the available water resources as the global population is growing everyday and the changes in the climate are forecasted in order to increase the water stressing such as flooding and drought. Flooding from the storm water has caused a serious damage to the infrastructure and major damage to the environmental ecosystem in terms of the erosion, flooding, potential pollution, sedimentation, etc. Storm water can be viewed either as a very costly threat to the environmental protection and of social welfare. In other words, it can also be seen as an opportunity in order to promote micro-watershed sustainable development through the use of the decentralized storm water solutions such as the Rain Water Harvesting (RWH). The overall objective of this research work is to show that how RWH is a very best sustainable solution to the storm water management. A study is conducted to find out whether RWH could ease future climate change effects on the storm water and help to restore the natural predevelopment storm water flow patterns; therefore, improving the quantity and the quality of storm before the runoff enters the receiving waters. RWH also was tested to determine whether it was a financially practicable answer to storm water management. In order to conduct an urban storm water impact assessment, hydrologic discharge data were collected from an outlet storm-sewer in the East Campus Drainage Area (ECDA) 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 with a conventional subterranean storm water 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 storm water quantity peak runoff by 55% and total volume runoff by 49%. 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 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 storm water management facilities.

METHODOLOGY

STUDY AREA

The East Campus Drainage Area (ECDA) is part of the Main Campus Basin, which is one of the four watershed basins Penn State maintains and preserves. With a total of 129 acres, the ECDA makes up a third of the Main Campus Basin and has an intensively developed land use with 66.2 acres (51.1%) of the area impervious. Buildings make up the largest percentage of the total imperviousness in the ECDA with 21.7 acres (16.8% of the total area), compared to roads (7.78 acres or 6.01%), parking (18.3 acres or 14.1%), sidewalks (14.0 acres or 10.8%), and impervious sports areas (4.39 acres or 3.39%). This is significant because buildings are the ideal catchment surface for rainwater harvesting.

The Main Campus storm water management utility is a 100% gravity flow system that is maintained by Penn State University, which works closely with the State College Borough because they share discharge right-of-ways (PSU, 2007b). The ECDA discharges storm water into the University Park Storm Drain System at the University Drive – College Avenue cloverleaf manhole on the southeast corner of campus (see Figures 3.1.2 and 3.1.3). The watershed outlet at the University Drive cloverleaf manhole discharges into the Duck Pond, which then flows into Slab Cabin Run, and thence into Spring Creek, before finally entering and travelling down the Susquehanna River to the Chesapeake Bay. Figure 3.1.4 shows the Spring Creek watershed in detail. Penn State is concerned about the direct impingement storm water runoff has on the local watershed and promotes the use of conservation design practices. Both the Spring Creek and Susquehanna Watersheds are forecasted to continue developing and growing; therefore, storm water runoff quantity and quality must be observed closely and managed sustainably.

WATER USAGE DATA

Records of water usage data were obtained from the Office of the Physical Plant (OPP) at Penn State. The 2005-2007 average water volume pumped from eight wells in two different well fields at University Park was 2.28 million gallons per day or a total of 835 million gallons of clean drinking water per year. With a population of over 41,000 at University Park, the average water consumption equates to 54 gallons/person/day. Even though enrollment rates have increased steadily over the past 30 years and new construction projects are initiated each year, Penn State actually has decreased its total yearly water consumption by 27% from 1981 to 2006 (PSU, 2000). The reduction in water consumption can be attributed to water efficiency improvements (i.e., low flow toilets, urinals and shower heads) and updating the efficiency of the West Campus Steam Plant, which accounts for 9% of the total water consumption on campus (PSU 2007b).

FLOW DATA

Storm water quantity data were collected from the 60 in. diameter Main Campus storm water pipe and the 48 in. diameter East Campus storm water pipe using a Hach Sigma 930 flow meter located at the cloverleaf manhole. The Hach Sigma 930 flow meter records the water depth (in inches) with a submerged pressure transducer and water flow velocity (in feet per seconds, fps) using sound waves and applying the Doppler principle (Hach Company, 2006). The data logger recorded water depths and velocity readings for storm water discharges in both pipes in 5-minute intervals for the study period beginning 6/06 and ending 12/07. Figure 3.2.1 shows the author collecting data at the cloverleaf manhole with the Hach Simga flow meter. The sampling setting of 5 minutes, instead of every 15 minutes, was chosen in order to capture more precise hydrographs. The water depth data are used to calculate cross-sectional areas of flow, which were combined with flow velocities to provide the volumetric flow rates of storm water through the pipes (See Appendix A.1). The flow meter was intended to simultaneously collect discharge data from both the 60 in. diameter Main Campus storm water pipe and the 48 in. diameter East Campus storm water pipe (Figure 3.2.2). The flow meter connected to the 60 in. diameter Main Campus pipe was not calibrated correctly and therefore the data collected could not be used. For this reason, the thesis scope was narrowed such that the study area was restricted to the ECDA. The 48 in. diameter East Campus runoff data could not be used directly because the 48 in. diameter pipe had a 6 in. diameter coaxial pipe running within it. In order to convert the measured height and velocity readings to discharge, the effective area had to be calculated for both storm water pipes. In the case of the 48 in. diameter pipe with the coaxial pipe inside it, the effective area of the 6 in. diameter pipe had to be subtracted from the 48 in. diameter pipe in order to calculate the correct runoff values. (See Appendix A.2 for effective area calculations for a pipe with a coaxial pipe inside it.) The 6 in. diameter coaxial pipe carries storm water from the storm water detention facility

the Duck Pond) back through the ECDA to cool the Breazeale Nuclear Reactor. The Breazeale Nuclear Reactor pumps 340 gallons per minute of water through the 6 in. diameter pipe to cool the 1 MW thermal reactor in its 71,000 gallon tank. After the water is used at the Breazeale Nuclear Reactor, it is released directly into the East Campus Drainage Area storm water system at a fairly constant rate. The Combustion Lab and the Research Boiler Lab also use storm water from the 6 in. diameter return pipe for research purposes, but do so at irregular times, and then release this water directly into the 48 in. diameter storm water pipes (personal communication with M. Morlang, Breazeale Safety Representative (Morlang, 2008)). For this study, the water discharged by these two buildings is presupposed to be insignificant.

After the effective area flow of the 6 in. diameter pipe is subtracted to calculate the correct runoff flow, the water that is used by Breazeale also must be subtracted in order to correct total measured flow to represent just storm water runoff flow from precipitation. The Breazeale flow was fluctuates consistently; therefore, the average runoff flow from the Breazeale Nuclear Reactor was calculated by averaging the constant discharge in the 48 in. pipe during periods when no rain events occurred. This gave the runoff data during storm events a near to zero discharge baseline in order to accurately represent runoff from storm events.

PRECIPITATION DATA

During the one-year analysis period of this study (2007), 33.8 in. of total rainfall data were cataloged at the University Weather Station on the Main Campus Watershed. Table 4.1.1 shows the monthly percent difference between the 100-year average rainfall data and the observed rainfall data of 2007. For the 2007 data, rainfall in the Main Campus Watershed was 11.9% less than the 100-year average, including differences in rainfall of -50.9% in May and -40.7% in September. This less-than-average rainfall in the fall of 2007 prompted the Department of Environmental Protection to declare a drought watch in most of the Commonwealth of Pennsylvania, including Centre County (DEP, 2007; Dvorak, 2007).

The decrease in precipitation in 2007 in the Main Campus Watershed was accompanied by a lesser number of larger volume rain events and also decreased the amount of higher intensity storm events. The 2007 rainfall data were broken into 122 precipitation events in which 46 of the rainfall events had less than 0.05 in. of rain total. Precipitation events of less than 1/20th of an inch (0.060 in.) rarely generate runoff, meaning that for this study, only the 76 events that produced 0.060 in. of rain or greater were studied and analyzed.

Intensity-duration-frequency (IDF) curves for State College were produced using current data available at the National Oceanic and Atmospheric Administration (NOAA) website (NOAA, 2008). The probabilistic relationship between the precipitation duration, rainfall intensity, storm return periods and the 76 precipitation events are represented graphically in Figure 4.1.1. The 76 precipitation events then were broken down to 1-, 2-, 5-, 10-, 25-, and 100-year period events.

CONCLUSION

This thesis has shown how RWH systems have a sustainable and positive impact on storm water management by reducing surface runoff compared to conventional storm water systems, decreasing potential water pollutant loadings, increasing water conservation and being cost effective. It was concluded that in order to get out of dilemmas linked with future population growth, land use changes or urbanization, and weather change, decisions must be made in a micro scale by understanding the macro-sustainability effects. The collected storm water runoff data were explained and the methods of the proposed analysis were defined. The ECDA-SWMM model was calibrated and successfully simulated peak runoff and total volume from five storm events within ±10% of the observed flow. The model was utilized to run past, present and future scenarios which included a pre-colonial scenario, a RWH scenario, and a future climate change scenario with and without the use of RWH. Results from these scenarios demonstrated that RWH was able to reduce the current peak and volume flows from the ECDA by 45% and also was able to mitigate future climate change effects of increased precipitation. These scenarios included:

(1) A demonstration water savings analysis,

(2) A monetary evaluation of a usual storm water facility being built with a RWH system.

(3) A simplified future analysis of the use of RWH facilities within Penn State’s University Park Master Plan. Results from the financial analysis show that through the use of RWH systems as decentralized storm water facilities in place of green roofs and conventional storm water detention systems, Penn State could save between $15 and $25 million dollars in the next 30 years.

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