Hydrologic Impacts of Exceeding Zoning Ordinances. on Impervious Lot Coverage: TR-55 modeling of three. Zoning Districts in Shippensburg Borough

Hydrologic Impacts of Exceeding Zoning Ordinances on Impervious Lot Coverage: TR-55 modeling of three Zoning Districts in Shippensburg Borough Practical Exam-Revisions Kristina Everetts November 19, 2013

Introduction Many municipalities, such as Shippensburg Borough, have zoning ordinances that limit the percentage of impervious lot coverage in their different zoning districts. Residents and developers can apply for variances or exceptions to the zoning restriction, to the zoning code that can allow them to go above that maximum percent of impervious coverage. Impervious coverage is exemplified by primarily as driveways, parking areas and rooftops. These coverage types do not allow the infiltration of rainfall, which produces storm runoff. Storm runoff can have detrimental effects on the natural environment, such as a lower groundwater recharge rate, flooding and increased amounts of pollutants and sediment in the local waterways. The purpose of this report is to analyze the hydrologic impacts of exceeding the lot coverage limits in three zoning districts in various scenarios within the Shippensburg Borough and will then be repeated to reflect the usage of porous pavement to the maximum extent reasonable per zoning district. The results produced from this analysis will then be interpreted in the broader context of stormwater management. Review of Literature The current Shippensburg Zoning Ordinance was adopted by the Borough Council in 2003 to protect and promote safety, protecting amenity, convenience, future governmental, economic, practical, and social and cultural facilities, development and growth, as well as the improvement of governmental processes and functions, and to guide uses of land and structures, type and location of streets, public grounds and other facilities. (Shippensburg Borough Council 2003). This ordinance divides the borough into multiple zones; this research will only focus on three zoning districts. Those districts are Residential Low-Density (R-1), Residential Medium/High-Density (R-3), and Commercial (C-1). 2

Stormwater management is more than just the management of water, but it also includes the protection, maintenance, reclamation and restoration of our water resource s quality and quantity. The main goal of stormwater management is to mimic natural (pre-development) hydrology to keep the total volume of surface runoff in balance with the amount of water that infiltrates or is transpired. Urbanization through increased impervious coverage alters the flow paths of stormwater runoff, which can have destructive impacts to water resources such as flooding and poorer water quality. Best management practices (BMPs) are mitigation measures implemented in watersheds for the purpose of controlling minor flooding and improving water quality (Gilroy and McCuen 2009). This research focuses on the effects of one type of BMP, porous pavement, and its ability to reduce stormwater runoff. The use of porous pavement has many benefits. Since it is used in the construction of parking lots and sidewalks it does not take up any additional land area as other stormwater management techniques, such as retention basins would. This creates a more attractive landscape. The ability to allow water to infiltrate into the pavement eliminates the risk of ponded water. This decreases the danger of hydroplaning and road glare especially at night. Porous pavement is also very important in the recharge of groundwater (Meierdiercks et al. 2010). The layered design of the pavement system allows stormwater to infiltrate the surface and then percolates through a subsurface into the soil reducing stormwater runoff (Jayasuriya 2007). Porous pavement s layered design starts with a high void layer of pavement at the surface, with an infiltration bed below it, which contains a coarse stone aggregate layer that has a void space of about 40%. It is this infiltration bed that allows the stormwater to slowly infiltrate into the native soil for groundwater recharge (Horst 2011; Kevern et al. 2010 and Welker et al. 2012). 3

Study Area The Shippensburg Borough is an older established community located in south-central Pennsylvania within the Cumberland Valley, which is a limestone floored valley. Shippensburg has a temperate climate with a yearly mean temperature of 55.7 Fahrenheit and the area averages 40 inches of precipitation per year (NOAA 2013). Rainfall in the Shippensburg area has a Type II distribution, which means that within a 24-hour rainfall the rain starts gradually, and at approximately the 12 th hour the rainfall is at its highest intensity. That highly intense period only lasts about an hour, but it produces the highest about of rain. After that highly intense period the rain returns to a gradual fall until the storm is over at approximately the 24 th hour (USDA 1986). The borough is divided into multiple zoning districts, but this research only focuses on three of them. Residential low-density (R-1) district primarily permits single-family detached dwellings with a lot coverage of no more than 30% of the lot covered with impervious surfaces (Shippensburg Borough Council 2003). In the Shippensburg Borough lots in this district consist of single family homes of various sizes, most of those homes have attached two-car garages, and paved driveways that could accommodate many vehicles. Also, these lots have patios, pools and lawns of various sizes (Google Earth 2007). Residential medium/high density (R-3) district permits single-family detached dwellings as well as allows many conditional uses such as multifamily dwellings with more than six units, group housings, home occupations and day-care and fitness centers. R-3 has a lot coverage of no more than 50% of the lot covered with impervious surfaces (Shippensburg Borough Council 2003). In the Shippensburg Borough lots in this district consist of single family homes of various sizes, multifamily apartments, and very few garages and pools. These lots also contain paved 4

driveways that could accommodate fewer vehicles then the low-density (R-1) district and these lots contain various sized patios and lawns as well (Google Earth 2007). The final zoning district in question is the commercial district (C-1). It allows the property to be developed into most commercial and professional uses. The lot coverage of C-1 has to be no more than 70% impervious surfaces (Shippensburg Borough Council 2003). In the Shippensburg Borough lots in this district consist of primarily buildings and parking lots for those building. There is very little lawn space in this district (Google Earth 2007). Shippensburg Borough lies primarily on two different soil types, the Murrill-Laidig Buchanan Association and the Hagerstown-Duffield Association, which are relatively well drained soils (Zarichansky 1986). The NRCS has classified many soils into four groups based off runoff and infiltration potential; a type A has the highest infiltration capacity and a type D has the lowest infiltration capacity. Both the Murrill-Laidig Buchanan Association and the Hagerstown-Duffield Association are type B soils (Bedient et al 2008). Methods and Results The primary method used in this research is modeling with the use of Technical Release 55 (TR-55) (USDA 1986). It is a simplified technique for estimating runoff in small urban watersheds. This research will use it to estimate the runoff for the three zoning districts that were mentioned above, in multiple scenarios including different lot coverages (three for each district), two site areas (for each district), and three design 24-hour storms (for each district and scenario). The whole analysis will also be repeated assuming that porous pavement was used to the maximum extent reasonable for each zoning district. Table one depicts the zoned and 5

variance lot coverages along with the two different site areas for each district and table two depicts the rainfall amounts for three 24-hour storms. Zoning District Maximum Under Current Zoning Code Impervious Lot Coverage 1 2 Site Areas A Site Areas B R-1 30% 40% 60% One 1-acre lot 100 1-acre lots R-3 50% 60% 80% One 0.25-acre lot 100 0.25-acre lots C-1 70% 80% 90% One 5-acre lot One 100-acre site Table 1. Zoned and Lot Coverage percentages and site areas. Recurrence Interval 24-hour Rainfall Amount (inches) 2-year 2.79 10-year 4.05 100-year 6.69 Table 2. Rainfall amounts for design storms (NOAA 2013). TR-55 uses the runoff equation, Equation One below, to calculate the runoff (Q) of each zoning district in each of the various scenarios. The runoff equation takes into account the 24-hour rainfall amount (P) and the runoff curve number for that zoning district and scenario, which is calculated by using the weighted CN method as outlined by Bedient et al (2008). This method of weighting the curve number is done by multiplying the percent of each land cover type within each zone (impervious, lawn, and porous pavement) by the curve number of that specific land cover. Those resulting values are then added together to get the weighted CN value for that zone and scenario. Table 4 outlines those resulting weighted CN values and appendix A outlines the calculations. Q = [P 0.2(1000 CN 10)]2 P+0.8( 1000 CN 10) Equation one: Runoff Equation 6

The percent imperviousness of each zoning district and subsequent scenario is given in table one above for the current zoning code and for variances one and two, but when the model is run with porous pavement to the maximum reasonable extent one must calculate the percent of remaining impervious pavement. Porous pavement can only replace impervious surfaces such as sidewalks, driveways and parking lots, not rooftops, pools and roadways. It cannot replace roadways because the structure of porous pavement is not strong enough to support the constant traffic on a roadway. Zoning District R-1 In zoning district R-1 at site area A (one 1-acre lot) the percent of imperviousness was determined by first doing a Google Earth (2007) survey of ten houses and lots within the R- 1 zoning district in the Shippensburg Borough. This survey was done in order to figure the average house size in relation to the amount of imperviousness on lots currently in the borough. The survey looked at the square footage of those ten homes and their attached garages, the square footage of their driveways, walkways and pools, if the lot had one (complete survey results can be found in appendix B). According to the completed survey, the average size of houses and attached garages in zoning district R-1 is 3,995 square feet. That means that the house and garage have an impervious footprint of 3,995 square feet, which is equal to 9.17% of one acre. The average driveway and walkway, according to the survey, has a footprint of 2,111 square feet, which is equal to 4.85% of one acre. Since almost half of the houses surveyed had pools, the average pool size was included in the total calculation of imperviousness. The average pool in Shippensburg s R-1 zone has a 708 square foot impervious footprint, which is equal to 1.63% of one acre. Houses in this zone are likely to have patios of some size, but that average size was difficult to calculate on Google Earth. So, a basic sized patio of 100 square feet (0.23% 7

of one acre) was also included in the total calculation of imperviousness. Once all those values were determined they were broken up into two categories: impervious and transferable into porous pavement. The total percent of impervious surfaces is 10.8% (9.17% house/garages + 1.63% pools), and the total percent of possible porous pavement is 5% (4.85% driveways/walkways + 0.23% patio). At site B in zoning district R-1(100 1-acre lots) the percent of imperviousness was calculated somewhat differently since the 1-acre lot is part of a 100 acre development. Housing developments need access roads to each lot and into the development itself. The area for these access roads is usually included in the 1-acre lot. Average roadways are 9-12 feet in width per lane without street side parking (Penn State 2005). While some developments do include street side parking in their planning, it was excluded in this model based on the properties of the developments surveyed through Google Earth. For this scenario an assumed lane width of 12 feet was used based on the fact that the development is rather large and contains many lots. To determine the area of each lot occupied by the road each 1-acre lot was assumed to be a square (208.7ft x 208.7ft). The length of the roadway side was then multiplied by the 12 foot width of the road to get an area of 2,504.52 square feet, which was then multiplied by 75 1 (75 non-corner lots) to get a total area of roadways from non-corner lots in the development of approximately 187,839 square feet. For the corner lots the length of roadways was multiplied by two sides (2,504.52sq ft x 2) to get 5009.04 square feet, which was then multiplied by the remaining 25 lots to get 125,226 square feet. So, the total amount of roadways in the development is 313,065 square feet or 7.2 acres. 1 Based upon developments surveyed, an approximate one out of four houses was found to land on a corner lot. When this ratio was applied to the Site B scenario, 25 out of 100 lots were found to be corner lots. 8

In addition to the roadways within the development the total amount of imperviousness still needs to include the footprints of houses and garages, driveways and walkways, patios and pools. Assuming the same averages found in appendix B, houses and garages occupy approximately 9.2 acres per 100 acres; driveways and walkways occupy 4.8 acres; patios occupy 0.23 acres; and pools occupy 1.6 acres. So, there is a total of 18 acres or 18% of impervious surfaces (7.2 acres roadways + 9.2 acres houses/garages + 1.6 acres pools) and a total of 5.03 acres or 5% of possible porous pavement (4.8 acres driveways/walkways + 0.23 acres patios). Zoning District R-3 In zoning district R-3, at site area A (one 0.25-acre lot) the percent of imperviousness was calculated by the same method as district R-1. The average size house in the R-3 district in the Shippensburg Borough, according to the same Google Earth (2007) survey, is 2,072 square feet 2. That means that the house has an impervious footprint of 2,072 square feet, which is equal to 4.75% of one acre. The average driveway and walkway, according to the survey, has a footprint of 788 square feet, which is equal to 1.81% of one acre. Houses in this zone are also likely to have patios of some size, so a basic sized patio of 100 square feet (0.23% of one acre) was also included in the total calculation of imperviousness. Once all those values were determined they were broken up into two categories (same as R-1): impervious and transferable into porous pavement. The total percent of impervious surfaces is 4.75% (4.75% house/garages), and the total percent of possible porous pavement is 2.04% (1.81% driveways/walkways + 0.23% patio). These percentages are relative to an acre, meaning the surface areas are being 2 The average square footage for district R-3 does not include a garage, because none of the houses surveyed or their neighbors had garages on their lot. 9

compared to a plot of land larger than the one they actually occupy. In order to correct for this the surface areas were multiplied by four, effectively quartering the lot size and leading to a total percent of 19% as impervious surfaces and total percent of 8.2% as possible porous pavement. At site B in zoning district R-3 (100 0.25-acre lots) the percent of imperviousness was calculated by the same method as district R-1 at site B. For this 25 acre development a road width per lane of 12 feet was used with the same street side parking assumptions. To determine the area of each lot occupied by the road each 0.25-acre lot was assumed to be a square (104.36 ft x 104.36 ft). The length of the roadway side was then multiplied by the 12 foot width of the road to get an area of 1,252.32 square feet, which was then multiplied by 80% 3 (80 non-corner lots) to get a total area of roadways from non-corner lots in the development of approximately 100,185.6 square feet. For the corner lots the length of roadways was multiplied by two sides (1,252.32sq ft x 2) to get 2,504.64 square feet, which was then multiplied by the remaining 20% of lots to get 50,092.8 square feet. So, the total amount of roadways in the development is 150,278.4 square feet or 3.4 acres. In addition to the roadways within the development the total amount of imperviousness still needs to include the footprints of houses, driveways and walkways, and patios. Assuming the same size averages as found in appendix B, houses occupy approximately 4.75 acres; driveways and walkways occupy 1.8 acres; and patios occupy 0.23 acres. So, there is a total of 32.8% of impervious surfaces (roads +houses) and a total of 8% of possible porous pavement (driveways/walkways + patios). 3 Based upon developments surveyed, an approximate one out of five houses was found to land on a corner lot. When this ratio was applied to the Site B scenario, 20 out of 100 lots were found to be corner lots. 10

Zoning District C-1 In zoning district C-1, in site area A (one 5-acre lot) and B (one 100-acre lot) the percent of imperviousness was determined by first doing a Google Earth (2007) survey of four commercial lots within the C-1 zoning district in the Shippensburg Borough. This survey was done in order to figure the average building size in relation to the amount of imperviousness on lots currently in the borough (complete survey results can be found in appendix C). According to the completed survey, the average size of commercial building in the Shippensburg Borough in relation to a five acre lot is 1.19 acres. This was calculated by first determining the square footage of the average Shippensburg commercial building and lot and converting it into acres. Once in acres a ratio adjusting it to a five acre lot was determined. This was done because the current commercial lots in Shippensburg vary greatly in size, so the ratio made all of them equal. Once all the lots and building sizes were based on a five acre lot, the average building size was determined. The average building size on a five acre lot is 1.19 acres, which is 23.8% impervious surfaces 4. The average paved parking area on a five acre lot is 2.59 acres, which is 51.8% 5. That 51.8% of parking area can be converted into porous pavement. All of the parking area can be converted to porous pavement because in a five acre commercial lot and building there would not be much constant heavy truck or vehicle traffic; mostly irregular occurrences such as deliveries that would only occur a few times a week. Since the lot size is much larger at site B the amount of imperviousness was calculated slightly differently due to high volumes of traffic and heavy truck traffic. Site B would be the size of a commercial building such as a shopping center. The difference in imperviousness is due to that high volume of traffic and truck traffic, so 4 This percentage was just adjusted up to accommodate the larger 100 acre lot. 5 This percentage was just adjusted up to accommodate the larger 100 acre lot. 11

access roads and truck parking areas must be calculated as impervious and not possible porous pavement. The amount of roadways within each size shopping center was calculated by assuming that the 100-acre lot is square (2,087.1 ft x 2,087.1 ft). Most shopping centers have an access road that follows the perimeter of the lot, which is oftentimes a two lane road. That amount of imperviousness was calculated by multiplying 2,087.1 feet by 24 feet (two lane roadway width) to get 50,090.4 square feet, which was then multiplied by 4 sides to get 200,361.6 square feet or 4.6 acres (4.6% of 100 acres) of roadway along the outer edge. Since there are designated areas for truck parking and loading within each center that amount must also be included in total amount of imperviousness that cannot be transferred into porous pavement. The approximate size of such an area is 5-acres (5% of 100 acres). The total amount of imperviousness at site area B is 33.8% (23.8% building + 5% truck parking + 4.6% access roads 6 ) That additional 10% of access roads and truck areas was taken from the 51.8% of possible porous pavement leaving 41.8% possible transfer to porous pavement. Also, this and all other percentages of imperviousness with maximum use of porous pavement can be found in table 3 below. 6 The percentage of truck parking and access roads was rounded up to a total of 10% to accommodate any additional possible high volume of truck traffic areas. 12

Zoning District (Sites A & B) Impervious Lot Coverage with Max. Porous Pavement Coverage % Impervious Lot Coverage Max. % Impervious Allowed Under Site Area Zoning (No ) 1 2 R-1A 30% 1 Acre Lot 10.8% 30.1% 40.1% R-3A 50% 0.25 Acre Lot 19.0% 50.1% 60.1% C-1A 70% 5 Acre Lot 23.8% 70.1% 80.1% R-1B 30% 100 1 Acre Lots 18.0% 30.1% 40.1% 100 0.25 Acre R-3B 50% Lots 32.8% 50.1% 60.1% C-1B 70% 100 Acre Lot 33.8% 70.1% 80.1% Table 3. Percentage of imperviousness in each zoning district and site area with and without the use of porous pavement. Once all of the percentages of imperviousness were determined for all scenarios, with and without porous pavement used to the maximum extent reasonable, the CN value for each scenario was then calculated using the weighted CN method above. The resulting values can be found in table 4. Zoning District (Sites A & B) CN Values of Zoning Districts without and with the use of Porous Pavement No Porous Pavement Porous Pavement to Max. Base CN Values 1 2 Site Area 1 2 R-1A 72 76 83 1 Acre Lot 66 76 80 R-3A 80 83 91 0.25 Acre Lot 70 85 90 C-1A 87 91 94 5 Acre Lot 82 94 95 R-1B 72 76 83 100 1 Acre Lots 69 74 79 100 0.25 Acre 80 83 91 R-3B Lots 75 83 87 C-1B 87 91 94 100 Acre Lot 84 94 95 Table 4. CN values for each zoning district and site area with and without the use of porous pavement. 13

Once all of the CN values for each scenario were determined, the data for each scenario was then entered into TR-55, which uses the runoff equation to calculate the runoff depths for each of the three storms in each of the different scenarios as described above. Those runoff depths (inches) can be found in tables 5 below. The depth of runoff was then converted into volumes for ease of comparison, and those values can be found in table 6 below. Discussion When comparing the runoff depths of each zoning district (R-1, R-3 & C-1) for the current zoning code with variance one (exceeding the maximum amount of imperviousness in the code by +10%) there is little variation between the two, but if the current code is compared with variance two (exceeding the maximum amount of imperviousness in the code by +20%) of each district the data shows much more variation. In table five the two year storm produced 0.69 inches of runoff under the current zoning code, but under variance two a two year storm produced 1.28 inches of runoff, which is 46% of the rainfall that the storm produced. In almost every zoning district and storm recurrence interval, the runoff amount caused by variance two is at least half and often times more than half of the amount of rainfall from that storm (table 5). By allowing developers and residents to exceed the current code s amount of imperviousness the Shippensburg Borough is allowing at least half or more of a storm s rainfall to runoff from impervious surfaces and not infiltrate into the ground. This lack of infiltration can lead to decreases in groundwater recharge and increases in flooding, which in turn can have detrimental effects on the local area. 14

Recurrence Interval Runoff Depth (inches) for Impervious Coverage Site Areas Use of Porous Pavement R-1A/B R-3A/B C-1A/B 1 2 1 2 1 2 2 Years 0.69 0.88 1.28 1.09 1.28 1.88 1.56 1.88 2.15 10 Years 1.5 1.78 2.33 2.08 2.33 3.07 2.68 3.07 3.37 100 Years 3.57 3.98 4.74 4.41 4.74 5.63 5.18 5.63 5.98 Recurrence Interval With the Use of Porous Pavement R-1A R-1 B R-3A 1 2 1 2 1 2 2 Years 0.45 0.88 1.09 0.56 0.78 1.04 0.60 1.41 1.79 10 Years 1.12 1.78 2.08 1.30 1.63 2.00 1.36 2.50 2.97 100 Years 2.96 3.98 4.41 3.26 3.77 4.30 3.36 4.96 5.52 R-3B C-1A C-1B 1 2 1 2 1 2 2 Years 0.83 1.28 1.56 1.22 2.15 2.24 1.35 2.15 2.24 10 Years 1.70 2.33 2.68 2.25 3.37 3.48 2.42 3.37 3.48 100 Years 3.88 4.74 5.18 4.63 5.98 6.10 4.85 5.98 6.10 Table 5. Runoff depths in inches for each zoning district with and without the use of porous pavement to the maximum.

R-1A R-1B R-3A 1 2 1 2 1 2 Recurrence Interval 2 Years 2,505 3,194 4,646 319,440 464,640 250,470 626 799 1,162 10 Years 5,445 6,461 8,458 646,140 845,790 544,500 1,361 1,615 2,114 100 Years 12,959 14,447 17,206 1,444,740 1,720,620 1,295,910 3,240 3,612 4,302 R-3B C-1A C-1B 1 2 1 2 1 2 Recurrence Interval 2 Years 98,918 116,160 170,610 34,122 28,314 34,122 566,280 682,440 780,450 10 Years 188,760 211,448 278,603 55,721 48,642 55,721 972,840 1,114,410 1,223,310 100 Years 400,208 430,155 510,923 102,185 94,017 102,185 1,880,340 2,043,690 2,170,740 R-1A R-1 B R-3A 1 2 1 2 1 2 Recurrence Interval 2 Years 1,634 3,194 3,957 203,280 283,140 377,520 545 1,280 1,624 10 Years 4,066 6,461 7,550 471,900 591,690 726,000 1,234 2,269 2,695 100 Years 10,745 14,447 16,008 1,183,380 1,368,510 1,560,900 3,049 4,501 5,009 Runoff Volumes (cubic feet) for Impervious Coverage Site Areas Use of Porous Pavement With the Use of Porous Pavement R-3B C-1A C-1B 1 2 1 2 1 2 Recurrence Interval 2 Years 75,323 116,160 141,570 22,143 39,023 40,656 490,050 780,450 813,120 10 Years 154,275 211,448 243,210 40,838 61,166 63,162 878,460 1,223,310 1,263,240 100 Years 352,110 430,155 470,085 84,035 108,537 110,715 1,760,550 2,170,740 2,214,300 Table 6. Runoff volumes in cubic feet for each zoning district with and without the use of porous pavement to the maximum. 16

If the runoff volumes for the use of porous pavement to the maximum extent reasonable were compared with the runoff volumes for just impervious coverage (table 6) the data shows that there is a significant reduction (in all districts and variances) in runoff if porous pavement was used to the maximum. The runoff from R-1A, variance two, 10-year storm produces 8,458 cubic feet of runoff, but if porous pavement was used to the maximum the runoff is only 7,550 cubic feet. That 900 cubic foot reduction in runoff means 900 more cubic feet are infiltrating into the ground to aid with groundwater recharge and lessen flooding in just that single lot. When examining the runoff values for the 100-year storm with porous pavement used to the maximum for each district (table 6) the values seem like they are still high, but since that storm produces such a high amount of rain any surface type, porous or impervious, would have a difficult time infiltrating all that rain. The pore space of the areas that allow infiltration will fill up before the storm is over so, the excess will just runoff (same with any 100-year storm). Overall, when comparing the different site areas there is a notable difference in runoff volumes. In R-3A (table 6), under the current code for a 2-year storm with maximum use of porous pavement the runoff is 545 cubic feet, but in R-3B (table 6) the runoff volume is 75,323 cubic feet. This is a huge increase in runoff volume by just placing the same 0.25 acre lot in a development with an additional 99 lots of the same size and description. Access roads for the development are the major cause of this large increase in volume because they cannot be transferred into porous pavement. When comparing the difference in runoff volumes for R-3A without porous pavement to R-3A with porous pavement for variance two, two-year storm the runoff volume increases from 2,114 to 2,695 cubic feet (table 6). This is due to the fact that with the use of porous pavement more impervious surfaces (larger garage, pool, etc) can be built to replace those previously

impervious surfaces (driveways, walkways etc). That increase takes away from previous lawn space, which has a lower CN value of 61 and replaces sections of it with a higher CN value of 98 (impervious) or 85 (porous pavement) which creates higher runoff volumes. These results are significant in the larger stormwater context in that it brings to light the fact of how much additional runoff is caused by increasing the amount of imperviousness in an area. Table five shows that by simply increasing the amount of imperviousness (by an additional 20% from the current code) in an area, that the runoff created by any storm is approximately half the total rainfall amount. Also, these results are significant because it shows how much runoff can be reduced with the use of porous pavement as shown in tables six. This reduction in runoff amounts could allow for increased use of porous pavement. Porous pavement also consumes less land area then other BMP s such as retention basins, so it may become more useful in areas where undeveloped land is at a premium. Conclusion If the Shippensburg Borough were to allow too many increases to zoning district variances it could ultimately have detrimental effects on the local area. With higher percentages of impervious surfaces there are less pervious areas where rainfall is allowed to infiltrate and to recharge the groundwater supply. Over time this could lead to lower base flows of local streams, which could lead to potential lower fishing and visitation rates due to the lower streams. Also, the increase in runoff caused by the increase in imperviousness can lead to higher rates of flooding, even in smaller storms such as the 2 or 10-year. Increasing the use of porous pavement in each district offers a way to increase the amount of imperviousness without increasing the runoff from that site that significantly. Additionally, porous pavement fulfills both the role of a driveway or sidewalk, while also fulfilling the role of a BMP, which is designed to controlling 18

minor flooding and improving water quality. This research also opens up future research into further examining the effects of porous pavement in various land uses and further development and examination of porous pavement s curve number. 19

References Bedient, Philip B. and Wayne C. Huber, Baxter E. Vieux, Hydrology and Floodplain Analysis. Prentice Hall: 2008: 98. Gilroy, Kristin L. and Richard H. McCuen, 2009. Spatio-temporal effects of low impact development practices. Journal of Hydrology 367 (3/4): 228-236. Google Earth, 2007. Shippensburg Pennsylvania. < www.earth.google.com >. Horst, Michael, and Andrea L. Welker, Robert G. Traver,2011. Multiyear Performance of a Pervious Concrete Infiltration Basin BMP. Journal of Irrigation and Drainage Engineering 352-358. Jayasuriya, L.N.N., 2007. Contributing to the sustainable use of stormwater: the role of pervious pavements. Water Science & Technology 56 (12): 69-75. Kevern, J.T. and K. Wang, V.R. Scharfer, 2010. Effect of Coarse Aggregate on the Freeze-Thaw durability of pervious Pavement. Journal of materials in Civil Engineering 469-475. Meierdiercks, Katherine L. and James A. Smith, Mary Lynn Baeck, Andrew J. Miller, 2010a. Analyses of Urban Drainage Network Structure and itsimpact on Hydrologic Respone. Journal of the American Water Resources Association (JAWRA) 46 (5): 932-943. National Oceanic and Atmospheric Association. 2013. Precipitation Frequency Data Server: Shippensburg, PA <http://www.nws.noaa.gov/climate/getclimate.php?wfo=ctp. >. Penn State: Civil and Environmental Engineering. 2005. Street Classifications and Standard. Residential Site Development Guidelines for Pennsylvania: Oversight Committee Meeting. Shippensburg Borough Council. 2003. Shippensburg Zoning Ordinance. Prepared by Civil & Environmental Design Group, Inc. http://ecode360.com/8126435#./8126435?&_suid=1382992130059034465739438585047 USDA (United States Department of Agriculture). 1986. Urban Hydrology for Small Watersheds. U.S.D.A. Soil Conservation Service Technical Release 55 (Second Edition). U.S. Government Printing Office, Washington, D.C. USDA. 2004. Hydrologic Soil-Cover Complexes. Part 630 Hydrology National Engineering Handbook. U.S. Government Printing Office, Washington, D.C. Welker, Andrea L. and James D. Barbis, Patrick A. Jeffers, 2012. A Side-by-Side Comparison of Pervious Concrete and Porous Asphalt. Journal of the American Water Resources Association 809-819. Zarichansky, J., 1986. Soil Survey of Cumberland and Perry Counties, Pennsylvania. U.S. Department of Agriculture, Soil Conservation Service, USDA, Washington, D.C. 20

Appendices: Current 1 2 Site A and B without Porous Pavement R-1 R-1 R-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 30 98 29.4 40 98 39.2 60 98 58.8 Lawn 70 61 42.7 60 61 36.6 40 61 24.4 Porous Pavement 0 85 0.0 0 85 0.0 0 85 0.0 Weighted CN 72.1 Weighted CN 75.8 Weighted CN 83.2 Site A with Max. Porous Pavement R-1 R-1 R-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 10.8 98 10.6 30.1 98 29.5 40.1 98 39.3 Lawn 84.2 61 51.4 56 61 34.2 41.34 61 25.2 Porous Pavement 5.0 85 4.3 13.9 85 11.8 18.56 85 15.8 Weighted CN 66.2 Weighted CN 75.5 Weighted CN 80.3 Site B with Max. Porous Pavement R-1 R-1 R-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 18 98 17.6 30.1 98 29.5 40.1 98 39.3 Lawn 77 61 47.0 61.5 61 37.5 48.8 61 29.8 Porous Pavement 5.0 85 4.3 8.4 85 7.1 11.1 85 9.4 Weighted CN 68.9 Weighted CN 74.2 Weighted CN 78.5 Appendix A. a. Calculation of weighted CN values. The percent of coverage is multiplied by the CN, and then those values are added together to get a total weighted CN value.

Appendix A. b. Calculation of weighted CN values. Current 1 2 Site A and B without Porous Pavement R-3 R-3 R-3 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 50 98 49.0 60 98 58.8 80 98 78.4 Lawn 50 61 30.5 40 61 24.4 20 61 12.2 Porous Pavement 0 85 0.0 0 85 0.0 0 85 0.0 Weighted CN 79.5 Weighted CN 83.2 Weighted CN 90.6 Site A with Max. Porous Pavement R-3 R-3 R-3 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 19 98 18.6 50.1 98 49.1 60.1 98 58.9 Lawn 72.8 61 44.4 28.3 61 17.3 14 61 8.5 Porous Pavement 8.2 85 7.0 21.6 85 18.4 25.9 85 22.0 Weighted CN 70.0 Weighted CN 84.7 Weighted CN 89.5 Site B with Max. Porous Pavement R-3 R-3 R-3 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 32.8 98 32.1 50.1 98 49.1 60.1 98 58.9 Lawn 59.2 61 36.1 37.7 61 23.0 25.2 61 15.4 Porous Pavement 8.0 85 6.8 12.2 85 10.4 14.7 85 12.5 Weighted CN 75.1 Weighted CN 82.5 Weighted CN 86.8 22

Appendix A. c. Calculation of weighted CN values. Current 1 2 Site A and B without Porous Pavement C-1 C-1 C-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 70 98 68.6 80 98 78.4 90 98 88 Lawn 30 61 18.3 20 61 12.2 10 61 6 Porous Pavement 0 85 0.0 0 85 0.0 0 85 0 Weighted CN 86.9 Weighted CN 90.6 Weighted CN 94 Site A with Max. Porous Pavement C-1 C-1 C-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 23.8 98 23.3 70.1 98 68.7 80.1 98 78 Lawn 24.4 61 14.9 0 61 0.0 0 61 0 Porous Pavement 51.8 85 44.0 29.9 85 25.4 19.9 85 17 Weighted CN 82.2 Weighted CN 94.1 Weighted CN 95 Site B with Max. Porous Pavement C-1 C-1 C-1 Cover type % of coverage CN % of coverage CN % of coverage CN Impervious 33.8 98 33.1 70.1 98 68.7 80.1 98 78 Lawn 24.4 61 14.9 0 61 0.0 0 61 0 Porous Pavement 41.8 85 35.5 29.9 85 25.4 19.9 85 17 Weighted CN 83.5 Weighted CN 94.1 Weighted CN 95 23

Survey of 10 Shippensburg Houses and the Average of those houses (square feet) R1 Houses 1 2 3 4 5 6 7 8 9 10 Average House & Garage 5,000 3,375 2,940 6,175 4,800 2,160 4,320 4,368 3,316 3,498 3,995 Driveway 1,600 2,350 990 988 480 1,768 3,312 2,100 768 824 1,518 Pool 540 612 1,035 646 708 Walkways 450 1,020 325 576 593 R3 Houses 2,750 2,400 1,860 900 2,355 1,715 4,350 2,064 1,040 1,290 2,072 Driveway/walk 462 462 462 462 714 1,860 510 1,105 600 1,240 788 Pool 595 595 Appendix B. Results of the Google Earth survey of ten houses and lots in zones R-1 and R-3 within the Shippensburg Borough. 24

Square Footage of C1 Sites Within Shippensburg Site #1 Site #2 Site #3 Site #4 Average Plot Sq Feet 34,680 164,855 680,000 206,400 271,484 Building Sq. Feet 8,160 21,000 210,375 18,800 64,584 Pavement Sq. Feet 19,575 47,625 438,550 58,700 141,113 Lawn Sq. Feet 6,945 96,230 31,075 128,900 65,788 Acreage of C1 Sites Within Shippensburg Site #1 Site #2 Site #3 Site #4 Average Acreage 0.80 3.78 15.6 4.74 6.23 Building Acreage 0.19 0.48 4.83 0.43 1.48 Pavement Acreage 0.45 1.09 10.1 1.35 3.24 Lawn Acreage 0.16 2.21 0.71 2.96 1.51 Adjusted Acreages of C1 Sites Based on Ratio to Five Acres Site #1 Site #2 Site #3 Site #4 Average Acreage 0.80 3.78 15.6 4.74 6.23 Ratio to 5 Acres 6.25 1.32 0.32 1.05 0.80 Building Acreage 1.17 0.64 1.55 0.45 1.19 Pavement Acreage 2.81 1.44 3.22 1.41 2.59 Lawn Acreage 1.00 2.92 0.23 3.11 1.21 Total acreage 4.98 5.00 5.00 4.98 4.99 Appendix C. The results of the Google Earth survey of commercial lots within the Shippensburg Borough and the calculation of the average building size on a five acre commercial lot. 25