University of Virginia. Moore s Creek Stormwater Management Master Plan Volume I. Prepared by

Transcription

1 University of Virginia Moore s Creek Stormwater Management Master Plan Volume I Prepared by Judith Nitsch Engineering, Inc. 186 Lincoln Street, Suite 200 Boston, Massachusetts JNEI Project #3534 November 5, 2002 Final December 31, 2002

2 Moore s Creek Stormwater Management Master Plan Final Report December 31, 2002 A Draft Moore s Creek Stormwater Management Master Plan was issued on November 5, In response to an from Robert Cooper (Virginia Department of Conservation and Recreation, VADCR) to Stephen Benz (Judith Nitsch Engineering, Inc.) dated December 19, 2002, the following changes were made to the Draft Moore s Creek Stormwater Management Master Plan and are incorporated in the Final Report dated December 31, 2002: 1. A summary sheet for the Baseline Conditions vs. Proposed Conditions was compiled based upon data found in Volume II. This summary table has been added to a new Appendix section, Appendix E in Volume I. The Table of Contents was also revised to include Appendix E. 2. The text on Page 1 of Volume I has been revised to state that the University of Virginia will check all projects for compliance with the Stormwater Master Plan and will issue a letter to VADCR for their final approval.

3 VOLUME I TABLE OF CONTENTS SECTION TITLE PAGE EXECUTIVE SUMMARY... v I. INTRODUCTION... 1 II. GOALS, PRINCIPLES, AND OBJECTIVES... 1 III. HYDROLOGY... 2 A. Existing Conditions Watershed Characteristics Moore s Creek Tributaries Land Cover Soils... 5 B. Former Studies University of Virginia Strategic Plan for Water Resources Management Moore s Creek Watershed Study Moore s Creek Watershed Assessment Letter West Grounds Stormwater Pond Improvements Rock Creek Stream Valley Master Plan East Precinct Parking Garage and Infrastructure Project-The University of Virginia Health Sciences Center... 8 C. Hydrologic Modeling Approach Methodology Hydrologic Models D. Baseline Conditions Model Analysis E. Unmitigated Hydrologic Model Analysis Watershed Sensitivity Watershed Response to Development F. Proposed Conditions Model Mitigation Analysis Buildout Analysis Selected Mitigation Measures G. Mitigation for Future Development i

4 TABLE OF CONTENTS (continued) SECTION TITLE PAGE IV. WATER QUALITY APPROACH A. Introduction to Water Quality Pollutants in Stormwater Water Quality Control on a Site-by-Site Basis Water Quality Control on a Regional Basis B. Natural Processes Ecosystems Characteristics of Streams, Ponds, and Wetlands The Benefits of Streams, Ponds and Wetlands C. Watershed Restoration Impacts to the Natural Drainage System Reestablishing Natural Ecological Processes Benefits of Watershed Restoration D. Pollutant Removal Mechanisms Physical Mechanisms Chemical Mechanisms Biological Mechanisms E. Regional Watershed Restoration Opportunities Daylighting Streams Creating Wetlands Creating Ponds Planting Native Wetland Species Creating Floodplains Incorporating Aquatic Benches Incorporating Vegetated Buffers F. Proposed Watershed Restoration Stadium Drainage Basin Brandon Drainage Basin Health Sciences Center and University Hospital V. WATER QUALITY A. Pollutant Removal Efficiencies for Existing BMP s West Grounds Stormwater Management Pond (Gilmer Pond) Gooch/Dillard Stormwater Pond Health Sciences Center Stormwater Management Pond B. Water Quality for Identified Future Development Projects Water Quality Volumes Pollutant Runoff Loads ii

5 TABLE OF CONTENTS (continued) SECTION TITLE PAGE C. Best Management Practices Strategies Stadium Drainage Basin Brandon Drainage Basin Health Sciences Center D. Water Quality Treatment Volumes E. Water Quality for Future Development F. Site-Specific Water Quality Management VI. COMPLIANCE WITH VIRGINIA STORMWATER MANAGEMENT REGULATIONS VII. CONCLUSION VIII. REFERENCES LIST OF FIGURES FIGURE TITLE PAGE 1 Watershed Rating Curve for 2-year Storm Design Watershed Rating Curve for 100-year Storm Design Hydrologic Criteria for the Modified Gooch/Dillard Pond Hydrologic Criteria for the Enhanced Extended Detention Basin Hydrologic Criteria for the Rainstore Unit Hydrologic Criteria for the Extended Detention Basin LIST OF TABLES TABLE TITLE PAGE 1 University Property within Drainage Areas Baseline Conditions Data Proposed Impervious Planning Areas within Changed Sub-basins 12 4 Unmitigated Model Data Analysis Areas and Discharge Points Health Services Projects Peak Flow Rate from Sub-basin MO-3C with Gooch/Dillard Pond Modifications Peak Flow Rate from Sub-basin MO-3A with proposed Enhanced Extended Detention Basin iii

6 LIST OF TABLES (continued) TABLE TITLE PAGE 9 Peak Flow Rate at the Stadium Drainage Basin Design Point Peak Outflow from South Lawn Development Site Peak Flow Rate from Sub-basin MO-5B Peak Flow Rate at the Brandon Drainage Basin Design Point Peak Flow Rate from Sub-basin MO-6B with proposed Extended Detention Basin Peak Flow Rate at the Health Sciences/University Hospital Design Point Peak Flow Rate at the MO-6A (Unmitigated) Design Point Sample Water Quantity Tracking Table Water Quality Volumes Pollutant Runoff Loads and Pollutant Removal Requirements Water Quality Treatment Volumes Sample Water Quality Tracking Table LIST OF APPENDICES APPENDIX A TITLE Tracking Table A.1 Stadium Drainage Basin Water Quantity Tracking Table Tracking Table A.2 Brandon Drainage Basin Water Quantity Tracking Table Tracking Table A.3 Health Sciences Center/University Hospital Area Water Quantity Tracking Table Tracking Table A.4 Stadium Drainage Basin Water Quality Tracking Table Tracking Table A.5 Brandon Drainage Basin Water Quality Tracking Table Tracking Table A.6 Health Sciences Center/University Hospital Area Water Quality Tracking Table B C D E Exhibit 1 Moore s Creek University Property Map Exhibit 2 Moore s Creek Drainage Area Stormwater Management Facilities Maintenance Guidelines Cox Report Stormwater Management Calculations for Health Sciences Center Pond Summary Tables for Baseline Conditions vs. Proposed Conditions iv

7 EXECUTIVE SUMMARY Judith Nitsch Engineering, Inc. (JNEI) has prepared this Stormwater Master Plan (SWMP) to support the growth and development of the University of Virginia within the watershed of Moore s Creek. The University of Virginia lies in the headwaters of many small creeks that drain in a southerly direction to join Moore s Creek en route to the Rivanna River. Through this SWMP, the University is attempting to improve the downstream erosion and flooding problems in Moore s Creek and its tributaries by implementing measures to reduce the peak rate of stormwater discharge both within UVA property and at the point where the Moore s Creek tributary branches exit UVA property. In addition, the incorporation of enhanced stormwater treatment measures will serve to improve the quality of stormwater both within the University property, as well as in the downstream receiving systems. The extent of future development identified by the University of Virginia is located along the southern portion of the University property where stormwater is collected and conveyed to Moore s Creek via one of three waterways. These include Rock Creek, a tributary of Rock Creek, and a city drainage pipe. JNEI has strategically planned stormwater mitigation and treatment strategies in three basin areas, each of which conveys stormwater to one of these three collection waterways. For the purposes of this SWMP, the three basin areas are referred to as the Brandon Drainage Basin, the Stadium Drainage Basin, and the Health Sciences/University Hospital Area. In order to evaluate the condition and to make recommendations regarding the University Basin Areas within the Moore s Creek Watershed, JNEI has undertaken a two-pronged approach. First, a comprehensive stormwater hydrology model was developed to assess the existing hydrologic condition of Moore s Creek. Using this baseline conditions model, JNEI was able to develop an understanding of this complex watershed under today s conditions. To evaluate the effects of future development, JNEI modeled development conditions based on future development projects identified by the University of Virginia in their current Master Plan. Through a series of workshop meetings held at the UVA, JNEI has presented the results and recommendations to the UVA in an effort to promote workable and realistic implementation strategies. The selected mitigation strategies intended to improve the flooding and erosion of downstream Moore s Creek include: Stadium Drainage Basin 1. Taking advantage of banked storage capacity remaining in the existing Gilmer Pond. 2. Increasing the Storage Capacity of Gooch/Dillard Pond and modifying the outlet. 3. Creating an enhanced extended detention basin upstream from existing Gilmer Pond. Brandon Drainage Basin 1. Promoting the greening approach at the South Lawn Development, where the post-development condition will contain less impervious area than the predevelopment condition. 2. Creating an underground detention basin to reduce the peak flow rate and volume for small storm events. v

8 Health Sciences/University Hospital Area 1. Taking advantage of banked storage capacity remaining in the existing Health Sciences Center Pond. 2. Creating an extended detention basin in the University Hospital Area. Stormwater quality measures within the basin areas include: Stadium Drainage Basin 1. Taking advantage of banked storage capacity for water quality treatment in existing Gilmer Pond. 2. Providing for water quality treatment through the increased storage in Gooch/Dillard Pond, as well as providing enhanced treatment through the addition of native vegetation, aquatic benches, and floodplains. 3. Creating a new enhanced extended detention basin associated with the Observatory Hill/Alderman Road Residence Cluster that incorporates a shallow marsh system providing additional pollutant removal through wetland plant uptake, absorption, filtration, decomposition, and settling. Brandon Drainage Basin 1. Promoting the greening approach to development for the South Lawn Project. 2. Providing vegetated filter strips, grassed swales, and/or biofiltration areas. Health Sciences/University Hospital Area 1. Taking advantage of banked permanent pool storage remaining for water quality treatment in the existing Health Sciences Center Pond. 2. Creating an extended detention basin upon development of areas outside the current Health Sciences Master Plan to provide pollutant removal through gravitational settling. All Development Projects 1. Providing pretreatment at development sites. This SWMP is intended to satisfy the Virginia Department of Conservation and Recreation s (DCR) requirements for stormwater management. As such, the level of development that has been identified and modeled in the SWMP should be acknowledged by the DCR upon their approval and review of site-specific project plans for sound engineering practices and consistency with the SWMP. Within this SWMP, JNEI has provided a simple methodology to track the projects that were anticipated and modeled within the basin areas. Thus, the University and the DCR will easily be able to compare the scopes and sizes of specific projects as they materialize and make certain the projects are consistent with the assumptions made in the SWMP. vi

9 I. INTRODUCTION Judith Nitsch Engineering, Inc. (JNEI) has prepared this Stormwater Master Plan (SWMP) for the University of Virginia (UVA). In order to support the growth and development of the University of Virginia within the watershed of Moore s Creek, the UVA seeks to develop its projects within the guidance parameters established by this SWMP. JNEI s Scope of Work for this SWMP consisted of stormwater modeling of existing conditions, modeling of future development, assessment of potential impacts on stormwater peak rate and stormwater quality, and determining stormwater mitigation and treatment measures. This SWMP will become the blueprint for stormwater management of the development projects the UVA has planned now and in the near future. As such, certain assumptions have been made regarding the scopes and sizes of developments within the Moore s Creek Watershed. As projects approach the completion of the design stage, they will be checked by the University of Virginia for compliance with the assumptions made in this SWMP. UVA will send a letter to the Virginia Department of Conservation and Recreation (DCR) stating the project s compliance with the SWMP. DCR will review each project and grant approval upon acceptance of the design with the objectives of the SWMP and their current design standards. II. GOALS, PRINCIPLES, AND OBJECTIVES The goals and objectives of this Master Plan include: To develop workable solutions to relieve the existing stressed stream condition of the Moore s Creek and its tributaries; To understand the baseline conditions associated with the existing conditions within the watershed; To evaluate the hydrologic sensitivity of the watershed; To model the development conditions associated with the UVA s build-out plans for the Southern portion of Campus; To support the UVA s desire to be responsible to the environment and to its downstream neighbors; To ensure compatibility with previous stormwater management planning; To implement realistic hydrologic mitigation and water quality treatment measures in support of the plans for development within the watershed, thus creating a blueprint for development of the UVA grounds; To develop onsite and/or local-type management approaches to stormwater quantity and quality, and To develop a stormwater management plan in accordance with the Virginia Stormwater Management Regulations addressing hydrologic and water quality issues associated with the UVA s development within the watershed. 1

10 III. HYDROLOGY A. Existing Conditions The existing conditions of the Moore s Creek Watershed within the UVA property were discussed in a report entitled University of Virginia Strategic Plan for Watershed Management by Andropogon Associates. Judith Nitsch Engineering Inc. (JNEI) used the information set forth in the Andropogon report as a basis for determining the existing conditions of the watershed for the hydrological analysis discussed in this report. In addition, JNEI used City of Charlottesville watershed maps and recent topographic information to refine the existing conditions assumptions set forth by Andropogon. 1. Watershed Characteristics The University of Virginia is within the headwaters of two major tributaries that drain to the Rivanna River and, ultimately, to the Chesapeake Bay. Located on the south of the UVA campus, one of the tributaries, Moore s Creek, is fed by many small creeks, which drain from the steep hills within the University of Virginia property. Between Ivy Road and Fontaine Road, small creeks flow down Lewis Mountain and Observatory Hill where they are collected in Morey Creek. Morey Creek flows in a southeasterly direction and joins Moore s Creek shortly after passing beneath the railroad tracks. Along Jefferson Park Avenue and the railroad, University storm drain systems and small creeks flow south and collect in Rock Creek, which joins Moore s Creek at the Charlottesville/Albemarle County line. For the purposes of stormwater management planning, Andropogon delineated the University property into 11 sub-basins that form the headwaters of Moore s Creek. Using the City of Charlottesville watershed map and recent topographic information, JNEI refined the Moore s Creek sub-basins identified by Andropogon and delineated 15 sub-basins as the Moore s Creek Watershed. The Moore s Creek Watershed sub-basin delineations are illustrated in Exhibit 2 of Appendix A. The Moore s Creek Watershed consists of University property, as well as City and County property. Many of the 15 sub-basins consist of land owned by the University, as well as residential neighborhoods adjacent to University property. As part of this study, JNEI determined the portion of the various sub-basins within the watershed that are University property. A summary of the findings is shown in Table 1. See also Exhibit 1 of Appendix A of this report for a plan summarizing these findings. Table 1 University Property within Drainage Areas SUB-BASIN IDENTIFICATION TOTAL DRAINAGE AREA (ACRES) TOTAL UVA AREA WITHIN DRAINAGE AREA (ACRES) PERCENTAGE OF DRAINAGE AREA ATTRIBUTED TO UVA MO-1A % MO-1B % MO-2B % MO-3A % MO-3B % MO-3C % MO-5A % MO-5B % MO-6A % 2

11 SUB-BASIN IDENTIFICATION TOTAL DRAINAGE AREA (ACRES) TOTAL UVA AREA WITHIN DRAINAGE AREA (ACRES) PERCENTAGE OF DRAINAGE AREA ATTRIBUTED TO UVA MO-6B % MO % MO-8A % TOTAL % 2. Moore s Creek Tributaries The University of Virginia lies within the headwaters of two Moore s Creek tributaries, which flow in a southerly direction from the University where they join Moore s Creek. These tributaries include Morey Creek and Rock Creek. Although a stream channel survey was not part of the scope of this study, JNEI compiled the information regarding the properties of these collection tributaries from United States Geological Survey (USGS) Maps and a report entitled Moore s Creek Watershed Study by Dewberry and Davis (1996). Stormwater runoff from the western portion of the University of Virginia campus (UVA sub-basins MO-1A, MO-1B, MO-7, MO-8A, MO-8B, MO-8C, and MO-9) is collected in drainage systems and small tributaries where it is conveyed beneath Route 29 and discharged into Morey Creek. Morey Creek travels in a south-to-southeasterly direction where it joins Moore s Creek just as it passes beneath the Southern Railroad. According to the analysis performed by Dewberry & Davis (1996) and as interpreted by the City of Charlottesville Engineering Department, stormwater from the southern portion of the University contributes to two primary waterways within the Moore s Creek Watershed namely Rock Creek and a tributary of Rock Creek. The area identified as the city s Brandon drainage basin (UVA Sub-basins MO-5A and MO-5B) conveys and discharges stormwater runoff to Rock Creek. Stormwater from this basin is conveyed under the railroad tracks south of Valley Road and into the Rock Creek basin. Rock Creek begins near the intersection of Jefferson Park Avenue (JPA) and Valley Road, travels southeast under the railroad tracks, under Cherry Avenue, and along Rock Creek Road to 5 th Street near Cleveland Avenue. Stormwater runoff from the City s Stadium Drainage Basin (UVA Sub-basins MO-3A, MO-3B, and MO-3C) is conveyed and discharged to a tributary of Rock Creek. The Rock Creek Tributary begins at the intersection of Stadium Road and Shamrock Road, travels under the railroad tracks, under Center Avenue, under Cherry Avenue, and along Mosely Drive and Cleveland Avenue to 5 th Street where it joins Rock Creek. At this point, Rock Creek travels in a southeasterly direction where it joins Moore s Creek just south of the Charlottesville City/Albemarle County line. Stormwater runoff from the University s Hospital/Health Sciences Area is conveyed through two large-diameter pipes beneath the railroad tracks and is also discharged into the Rock Creek basin where it flows along the boundary of the Orangedale and Nalle Street Basins, and crosses beneath the 5 th Street Extended (at the confluence of Rock Creek and the Rock Creek Tributary) and subsequently joins Moore s Creek. The Dewberry & Davis Report also documents the severe flooding and stream channel erosion problems that occur in Rock Creek and its tributary. Although some improvements have been made to this system, the report indicates there is still a 3

12 significant concern regarding the impacts of stormwater runoff of the existing Rock Creek stream channels. 3. Land Cover The existing land features of the sub-basins that contribute to the Moore s Creek Watershed vary greatly. Large portions of the watershed have been developed by the University and by residential development with houses, academic buildings, residence halls, paved parking lots, and driveways. Other areas have been cleared for the creation of grass lawns and landscaped areas. The land cover of the 15 sub-basins within the Moore s Creek Watershed is described below. The sub-basins are described first along the western portion of campus- from north to south, then along the southern portion of campus from west to east (Refer to Exhibit 2 of Appendix A). Sub-basin MO-7 lies at the northern foothills of Lewis Mountain. As the mountain itself is undeveloped, the majority of the sub-basin is developed with University Research and Industrial Facilities, as well as a residential development north of Ivy Road. Sub-basin MO-8A lies at the western foothills of Lewis Mountain. This sub-basin is largely wooded and undeveloped, with the exception of a small portion of the Aerospace Research Center. Sub-basins MO-8B, MO-8C, and MO-9 lie at the western foothills of Observatory Hill. Within these sub-basins, a small amount of development is found near the peak of Observatory Hill with the McCormick Observatory Buildings; however, the remainder of these sub-basins are largely wooded and undeveloped. Sub-basin MO-1A lies in the southeastern foothills of Observatory Hill. The sloping hill is wooded and undeveloped. The eastern portion of Sub-basin MO-1A, however, is developed with University Housing, as well as a residential neighborhood of approximately one-third-acre lots along Mimosa Drive. This residential district extends east into Sub-basins MO-1B and MO-2B where it becomes denser (one-quarter-acre lot) neighborhoods along Appletree Road, Pierce Avenue, and Maury Avenue. The southern portion of Sub-basin MO-3C is developed with University Housing areas, the largest being the Gooch/Dillard Dormitory, and associated walkways, driveways, etc. The northern portion is also developed with the water towers and water plant along Observatory Road. The middle portion of Sub-basin MO-3C, between the water plant and the Gooch/Dillard Dormitory, consists of a large area of woods. Sub-basin MO-3B is an extensively developed sub-basin. The northern portion of the sub-basin consists of the University Stadium, associated parking areas, University Engineering Buildings, University Housing, and the water plant. The southern portion of the sub-basin, south of Stadium Road, consists of residential neighborhoods with lots that are approximately one-quarter acre in size. The residential neighborhoods are less than half impervious as they contain houses, roads, and driveways, but also contain pervious grassed yards and landscaped areas. Sub-basin MO-3A is also a developed sub-basin as a large area consists of the Alderman Road Residence Cluster, Gilmer Hall, and the Aquatic and Fitness Center. Portions of MO-3A remain pervious as grassed lawns, landscaped areas, and a stormwater management pond. 4

13 The upper portion of Sub-basin MO-5A contains University Housing buildings and associated impervious areas, such as Olsson Hall, Thompson Hall, and Clark Hall. The remainder of the sub-basin consists of dense residential communities along Jefferson Park Avenue and Valley Road. These neighborhoods consist of houses and driveways on approximately one-quarter-acre lots with lawns and other pervious areas. The northern portion of Sub-basin MO-5B consists of hotels, pavilions, an amphitheater, University Housing, and other buildings, as well as associated walkways, driveways, roadways, and parking lots. However, the northern portion of this sub-basin also consists of large pervious areas such as The Lawn and other grassed and landscaped areas between walks and buildings. The southern portion of Sub-basin MO-5B is also developed with a University parking lot, the Student Nurses Dorm Area, and dense residential neighborhoods. Pervious areas within this sub-basin consist of grassed lawns and landscaped areas. The development of hotels, pavilions, and University Housing and other buildings also extends east into the northern portion of Sub-basin MO-6A, as well as The Lawn area. The northern portion of MO-6A also consists of University Health Sciences Buildings and a Heating Plant. The southern portion of Sub-basin MO-6A and all of MO-6B is also extensively developed with the University Hospital, parking facilities, research buildings and other impervious areas. A small portion of Sub-basin MO-6A also consists of a residential housing development along Monroe Lane and 15 th Street. 4. Soils The soils within the University property were classified in the report by Andropogon Associates. Andropogon Associates used the USDA Natural Resources Conservation Service (NRCS) soil classifications to analyze the soils that exist on the University Campus. The NRCS categorizes soils in one of four hydrologic soil groups: type A, B, C, or D according to the soil s ability to absorb water into the ground. Type A soils are the most permeable and Type D soils are the least. The soil classification determined by Andropogon Associates is summarized as follows: At the University, the Albemarle fine sandy loam and the Louisburg very stony sandy loam (Hydrologic Group B) are fairly well-drained and are located in the upland areas. The Culpeper fine sandy loam (Hydrologic Group C) have somewhat poorer drainage properties and are found in low-lying areas such as along stream channels. The report also suggested that undistributed soils will allow satisfactory infiltration, but developed sub-basins that have experienced a high degree of disturbance and excavation, will produce a soil condition that is less than suitable for infiltration. B. Former Studies Former studies have been performed within the Moore s Creek Watershed that provided useful information for the purposes of this hydrological analysis. The reports include the following: University of Virginia Strategic Plan for Water Resources Management, prepared by Andropogon Moore s Creek Watershed Study, prepared by Dewberry and Davis (August, 1996) 5

14 Moore s Creek Watershed Assessment Letter, prepared by the City of Charlottesville (May 7, 2002) West Grounds Stormwater Pond Improvements, prepared by CEGG Associates (January 2000) Rock Creek Stream Valley Master Plan, prepared by the Cox Company (December 2, 1997) East Precinct Parking Garage and Infrastructure Project-The University of Virginia Health Sciences Center, prepared by the Cox Company (August 27, 1997 revised May 4, 1998) 1. University of Virginia Strategic Plan for Water Resources Management The Andropogon report illustrates the effects of University development on the natural drainage system of the University of Virginia. It states that the large increase in impervious area over time has resulted in a greater volume of stormwater runoff downstream and a lesser volume of stormwater able to infiltrate into the ground. Along with the historical development, large portions of the natural drainage system have been altered or destroyed as streams have been placed in pipes and wetlands have been eliminated. The common mitigation practice associated with the historical development of the University has been to build earthen detention basins at the lowest point of a project site. However, the report concludes, this practice has done little to compensate for the total increase in stormwater runoff volume and to prevent pollutants from reaching the stream(s). The Andropogon report proposes a new sustainable approach to stormwater management through the concept of a Water Balance model. The Water Balance model uses the concepts of the hydrologic cycle to measure the amount of water both before and after development to evaluate how impervious surfaces and manmade drainage structures alter the natural cycle. In the first part of the model, Andropogon developed a predevelopment water balance that accounted for the natural cycle of water on an undeveloped segment of land for an average year. The second part of the model demonstrated the effects of development on the natural hydrological cycle in the post-development water balance. The major effect is due to the fact that a large portion of rainfall landing on developed land is unable to infiltrate into the ground. Instead, rainfall is converted directly into runoff. The effect of development, therefore, causes erosion and flooding due to the increased volume of stormwater runoff. In addition, the loss of baseflow to the streams causes drought to occur during storm events. Andropogon concludes that one way to mitigate the drought and flood effects of land development is to restore the water balance so it replicates the natural hydrologic cycle. It was determined that solutions to stormwater problems must go beyond simply fulfilling regulatory requirements when the natural hydrologic cycle is significantly changed by development, only solutions that replicate the pre-development water balance can solve the broad-range of stormwater management issues. The report proposes a stormwater management plan that combines land use and development strategies with the restoration of the natural drainage system and the use of better management practices for the sustainable future of the University. Land use strategies include the protection of stream headwaters, stream channels, associated riparian corridors, wetlands, and floodplains. Land development strategies include 6

15 providing recharge in the uplands, minimizing impervious and semi-pervious surfaces in new development, and minimizing grading and removal of natural vegetation. The proposed restoration strategies include daylighting streams and establishing wetlands, floodplains, and vegetated corridors. The proposed Better Management Practices include the use of recharge beds underneath pavement, porous pavement, infiltration trenches, vegetated swales, and detention basins retrofit in streams. Specifically, Andropogon explored several areas within the University to manage stormwater according to their proposed plan. Although the report did not conclude with a single solution, case studies were performed in order to demonstrate how the various principles of the stormwater management plan could be incorporated within the University. It was proposed that the stormwater management solution should vary depending on the level of development, but, in all cases, the goal should be to restore the natural drainage system to the greatest extent possible. A large portion of the Case Studies Section involved plans to restore Meadow Creek. One Case Study, however, involved the retrofit of a detention basin in the Valley below Gilmer Hall in order to control stormwater flows from the largely developed Sub-basin MO-3 and to provide additional water quality enhancement. The Andropogon report finally touches upon the treatment of the management of stormwater as a University-wide concern rather than on a site-by-site basis. The report recommends the University integrate sustainable water resources management into the University Master Plan and in strategies for future University growth. 2. Moore s Creek Watershed Study In the Moore s Creek Watershed Study, Dewberry & Davis performed a detailed hydrologic, hydraulic, and water quality analysis of the entire Moore s Creek Watershed. The report provided the City of Charlottesville and the County of Albemarle with a Stormwater Management Feasibility Study and a Watershed Plan for Moore s Creek. The important aspects of the Dewberry & Davis Report included the analysis of the flooding and erosion problems in the major tributaries of Moore s Creek. The report identified the two primary waterways that serve the southern portion of the City adjacent to the University of Virginia as the City of Charlottesville s Brandon (MO-5A & MO-5B) and Stadium Drainage Basins (MO-3A, MO-3B & MO-3C). These waterways were identified as Rock Creek and a Tributary to Rock Creek, respectively; whereby a detailed Channel Capacity Analysis was performed along various reaches. Through this analysis, the study provided an idea of the severe flooding and erosion in Rock Creek and the Tributary to Rock Creek downstream from the University of Virginia. The document also noted several large culvert replacement projects and stream stabilization projects that have been completed. The report proposes several alternative approaches to Stormwater Management to address existing and future drainage, flooding, and water quality problems in the Moore s Creek Watershed. Dewberry & Davis recommended an approach that involves implementing a regional approach to Stormwater Management that also includes onsite Stormwater Management controls. The report recommended that Albemarle County and the City of Charlottesville develop Stormwater Management Practices and Policies to prevent further stormwater impacts to the existing stream channels. 7

16 3. Moore s Creek Watershed Assessment Letter On May 7, 2002, the City of Charlottesville Neighborhood Development Services (Engineering Division) issued a letter to Judith Nitsch Engineering, Inc. for the purposes of the Stormwater Management Master Plan for the Moore s Creek Watershed. The letter used information compiled from two sources, which included the Dewberry & Davis Report and a report entitled City of Charlottesville Storm Drainage Study completed in 1979 by Huffman & Associates and William Roudabush, Inc. This letter synopsized the City of Charlottesville stormwater system as it relates to three areas adjacent to the University of Virginia property and proposed future projects within these areas. The three areas included the following: MO-5A & MO-5B Area including JPA and the South Lawn MO-3A, MO-3B, & MO-3C Area including Alderman Rd. and Scott Stadium MO-6A & MO-6B Area including the University Hospital The letter identified various pipe systems and culverts where the previous studies recommended pipe and culvert upgrades. The letter also addressed current erosion and flooding problems observed in the southern portion of the University and the downstream tributaries. The letter also provided a summary of the Stream Crossing and Channel Capacity Analysis performed by Dewberry & Davis. 4. West Grounds Stormwater Pond Improvements CEGG Associates prepared a report in January 2000 for the West Grounds Stormwater Management Pond (or Gilmer Pond) entitled West Grounds Stormwater Pond Improvements. This report included an erosion and sediment control narrative, a stormwater management narrative, TR-20 pre-development and post-development stormwater calculations, and detailed pond-routing calculations. In addition, the report included a comparison of the impervious area anticipated in the design of the pond to the impervious area actually constructed. Through this comparison, CEGG Associates calculated the impervious area banked for water quantity mitigation and water quality treatment in the existing pond. The banked impervious area for water quantity mitigation in the pond is 1.46 acres and the banked impervious area for water quality treatment in the pond is 4.74 acres. 5. Rock Creek Stream Valley Master Plan The Rock Creek Stream Valley Master Plan prepared by the Cox Company in December 1997 presented a summary of stream rehabilitation and storm drainage improvements in the Rock Creek Stream Valley. This plan proposed a series of improvements to the existing stream and drainage system in response to functional aesthetic and environmental quality objectives of the Stream Valley. This report was part of a comprehensive Master Plan by the University of Virginia and the City of Charlottesville and provided JNEI with an overview of the goals and recommendations for the improvement of the Rock Creek Drainage Basin downstream from the University of Virginia. 6. East Precinct Parking Garage and Infrastructure Project-The University of Virginia Health Sciences Center The Cox Company prepared Stormwater Management Calculations for the Stormwater Management Pond at the Health Sciences Center, with a final revision issued in May This report presented stormwater management and pond routing calculations for the stormwater retention pond in Sub-basin MO-6A. According to the Cox Company, 8

17 the pond was designed to accommodate the Full Development Scenario identified in Phases 1 through 4 of the 1996 Master Plan. The report concluded that the pond was designed to mitigate the Full Development scenario of 15.7 acres of impervious development. Based on the permanent pool storage capacity, the pond was designed to treat acres of impervious area for water quality treatment, an area greater than the Full Development scenario. Based on the level of development that has occurred since the issuance of the report, JNEI was able to determine the amount of impervious area that was considered in the Full Development scenario that has not been constructed at this time. JNEI concluded that there is impervious area banked in the existing pond for water quantity mitigation and water quality treatment. JNEI determined that there is approximately 3.43 acres of development area planned in the Cox Company report remains banked for water quantity mitigation of future development in the Health Sciences/University Hospital Area. In addition, approximately 8.61 acres remains banked for water quality treatment of future development projects within the Health Sciences/University Hospital Area. A summary of JNEI s determination of banked impervious areas for water quantity and quality is found in Section III.F.1.c and V.A.3 respectively. C. Hydrologic Modeling Approach 1. Methodology Using the Hydrologic Analysis from the Andropogon report, JNEI divided the Moore s Creek Watershed into 15 sub-basins. Each sub-basin is defined as an area where the runoff from that area flows to a particular design point. In this case, each sub-basin produces stormwater runoff that is collected by Moore s Creek through a creek or small tributary. All stormwater runoff from the Watershed is conveyed through various creeks and tributaries where they exit University property en route to Moore s Creek. Exhibit 2 of Appendix A illustrates the division of the 15 sub-basins in the Moore s Creek Watershed for the purposes of the hydrologic model in this report. The rate of runoff that reaches each point is determined by a number of factors: the slope and flow lengths of the sub-basin, the soil type of the sub-basin area, and the type of surface cover in the sub-basin area. The slope of the sub-basin area affects the amount of runoff and rate of runoff, as steep slopes produce more runoff and transport it at a faster rate than a flat site. This is due to the fact that, at a flat site, stormwater flows slowly and, therefore, has a greater opportunity to infiltrate into the ground before it flows away as runoff. The flow length of a sub-basin area is the longest hydraulic distance that runoff would have to travel to the design point. Flow length is an important factor in determining time of concentration (Tc). Tc influences the volume and rate of runoff. A low Tc will result in more runoff with a higher peak rate than a high Tc. The type of soil on a site also affects the volume and rate of runoff generated. The soil type found on a site determines the volume and rate at which water can be absorbed into the ground. The more water infiltrating into the soil, the greater the reduction in runoff volume and rate. The surface cover on a site refers to what is on the surface of a site, whether it is lawn, asphalt, brush, etc. Surface cover affects the rate and volume of runoff as certain covers 9

18 allow for more of an opportunity for water to be absorbed into the ground. A site covered with impermeable asphalt will not allow for any water to be absorbed into the ground, yet a site covered by vegetation will. Almost all the rain that falls onto asphalt or other impermeable covers will be converted to runoff. In addition, different vegetative covers have different properties with regard to producing runoff. Once JNEI determined drainage flow path lengths, slopes of the flow path, and surface cover types, the information was used to determine the Tc for the area. Based on the soil type, ground cover, and other factors, a weighted Curve Number (CN) was determined for each sub-basin. The peak runoff rates for various storm events were determined by inputting the weighted CN, Tc, drainage areas, and drainage information into the HydroCAD Version 6.00 stormwater modeling system computer program. The storm events were based on the 24-hour duration storm with a NRCS Type II storm distribution curve. The HydroCAD computer program uses the NRCS TR-20 method to model drainage systems. TR-20 (Technical Release 20) was developed by the Natural Resources Conservation Service to estimate runoff and peak discharges in small watersheds. TR-20 is generally accepted by engineers and reviewing authorities as the standard method for estimating runoff and peak discharges. HydroCAD Version 6.00 uses up to four structure types to analyze the hydrology of a given watershed. These structures are subcatchments (sub-basins), reaches, basins, and links. Subcatchments are areas of land that produce surface runoff. They are characterized by their area and weighted CNs. Reaches are generally uniform streams, channels, or pipes that convey water from one point to another. A basin is any impoundment that fills with water from one or more sources and empties via an outlet structure. Links are used to introduce hydrographs into a project from another source. 2. Hydrologic Models In order to develop a hydrologic analysis of the Moore s Creek Watershed, JNEI developed three separate model scenarios: 1. Baseline Conditions Model Baseline, or pre-developed, current conditions model 2. Unmitigated Hydrologic Model Post-development conditions model, without mitigation measures 3. Proposed Conditions Model Post-development conditions model, with mitigation measures D. Baseline Conditions Model 1. Analysis JNEI established the pre-development snapshot of existing conditions by determining watershed characteristics for the Moore s Creek Watershed. The baseline data documented the existing conditions of the Moore s Creek Watershed at the time the study began. JNEI used the CADD-based 100-scale mapping provided by the University as well as similar City of Charlottesville mapping to determine physical features and assess watershed characteristics. 10

19 Data developed for this Baseline Model scenario included: Existing soil types and land cover Delineation of Moore s Creek watershed and sub-basin areas (See Exhibit 2 of Appendix A) Flow paths and times of concentration for sub-basins Runoff Curve Numbers for sub-basins Due to the developed nature of some of the sub-basins and the completion of recent drainage modifications, JNEI found it necessary to further divide four sub-basins for the purposes of a more accurate hydrologic model. For example, a portion of Sub-basin MO-6A bypasses the stormwater management pond and, therefore, should be separated from the remaining area of Sub-basin MO-6A that is mitigated by the pond. The following table summarizes the data documented in the Baseline Model: Table 2 Baseline Conditions Data SUB-BASIN IDENTIFICATION DRAINAGE AREA (ACRES) PERCENT PERVIOUS (%) PERCENT IMPERVIOUS (%) PERCENT WOODED (%) SOIL TYPE TIME OF CONCENTRATION (Tc) WEIGHTED CURVE NUMBER (CN) MO-1A % 36% 47% C 15 minutes 81 MO-1B % 38% 0% C 14 minutes 83 MO-2B % 38% 0% C 17 minutes 83 MO-3A % 79% 7% C 11 minutes 92 MO-3B north % 85% 0% C 10 minutes 94 MO-3B south % 38% 0% C 11 minutes 83 MO-3C % 33% 14% C 10 minutes 82 MO-3C bypass % 10% 32% C 10 minutes 76 MO-5A % 85% 0% C 12 minutes 94 MO-5A south % 38% 0% C 13 minutes 83 MO-5B % 45% 0% C 22 minutes 87 MO-6A mitigated % 85% 0% C 12 minutes 94 MO-6A unmitigated % 85% 0% C 12 minutes 94 MO-6B % 85% 0% C 11 minutes 94 JNEI input these data into HydroCAD to generate a series of watershed conditions for four different design storm conditions. JNEI ran runoff models for the 2-, 10-, 25-, and 100-year storm events. The HydroCAD report for the Baseline Conditions Model can be found in Volume II of this report. The baseline conditions scenarios formed a basis from which to compare the watershed response to the proposed conditions models. E. Unmitigated Hydrologic Model 1. Analysis JNEI analyzed all sub-basins where the University of Virginia has identified potential future development projects at the time this study began. These future development projects are illustrated in the Master Plan in Appendix A, Exhibit 2. Within these subbasins, a net change due to a developed area was determined and identified as a 11

20 changed drainage area in the Unmitigated Model. JNEI used a conservative approach to model these changed drainage areas, as each future development project and associated impact area was estimated and assumed to be completely impervious (Curve Number 98). The proposed impervious development areas and the associated impervious impact areas within a sub-basin are collectively referred to as planning areas for the purposes of this report. The following table summarizes development projects within these identified sub-basins and the impervious planning area determined for the purposes of this Stormwater Management Master Plan (SWMP). Table 3 Proposed Impervious Planning Areas within Changed Sub-basins Changed Sub-basin Proposed Development Projects Identified by University Proposed Impervious Planning Area (acres) MO-3A Gilmer Hall Addition Aquatic & Fitness Center Addition Observatory Hall Addition % Additional Residential Housing MO-3B Chemistry Building Additions Mechanical Engineering Addition Material Science Building Addition 9.47 Chemical Engineering Research Addition Additional Unidentified MO-3C Unidentified 2.78 MO-5A MO-5B MO-6A mitigated MO-6A unmitigated MO-6B Olsson Hall Addition Additional Housing near Halsey Hall South Lawn Phase I South Lawn Phase II Parking Garage McCleod Hall Expansion Health Science Library Expansion South Parking Addition Phase III University Hospital Expansion Phase I and II Medical Research near McLeod MR-6, MR-7, MR-8 Additional Residential Housing Additional Medical Research McKim Hall Addition 1.06 University Hospital Addition Additional Unidentified The hydrologic properties of the planning areas, such as land cover, flow paths, and times of concentration, were estimated based on JNEI s determination of the size of the project and the conservative impervious development Curve Numbers of these changed areas. The unchanged portions of the developed sub-basins were modeled using the same hydrologic characteristics as in the Baseline Model. JNEI created an Unmitigated Hydrologic Model in order to determine the characteristics of the future developed watershed without incorporating mitigation measures. Data developed for the Unmitigated Model scenario included:

21 All information developed in the Baseline Conditions Model for unchanged sub-basins Land cover for sub-basins where proposed University development will occur Flow paths and times of concentration for sub-basins containing proposed development Runoff CNs for sub-basins containing proposed development The following table summarizes the data documented in the Unmitigated Model: Table 4 Unmitigated Model Data SUB-BASIN IDENTIFICATION DRAINAGE AREA (ACRES) PERCENT PERVIOUS (%) PERCENT IMPERVIOUS (%) PERCENT WOODED (%) SOIL TYPE TIME OF CONCENTRATION (Tc) WEIGHTED CURVE NUMBER (CN) MO-1A % 36% 47% C 15 minutes 81 MO-1B % 38% 0% C 14 minutes 83 MO-2B % 38% 0% C 17 minutes 83 MO-3A % 78% 8% C 11 minutes 92 MO-3A change % 100% 0% C 10 minutes 98 MO-3B north % 85% 0% C 10 minutes 94 MO-3B north change % 100% 0% C 10 minutes 98 MO-3B south % 38% 0% C 11 minutes 83 MO-3C % 41% 0% C 10 minutes 83 MO-3C change % 100% 0% C 10 minutes 98 MO-3C bypass % 10% 32% C 10 minutes 77 MO-5A % 85% 0% C 12 minutes 94 MO-5A change % 100% 0% C 10 minutes 98 MO-5A south % 38% 0% C 13 minutes 83 MO-5B* % 45% 0% C 22 minutes 87 MO-6A mitigated % 85% 0% C 12 minutes 94 MO-6A mitigated change % 100% 0% C 10 minutes 98 MO-6A unmitigated % 85% 0% C 18 minutes 94 MO-6A unmitigated change % 100% 0% C 10 minutes 98 MO-6B % 85% 0% C 11 minutes 94 MO-6B change % 100% 0% C 10 minutes 98 * Includes Changed Area Refer to Section III.F.1.b JNEI input these data into HydroCAD to generate a series of watershed response scenarios for four different design storm conditions including the 2-, 10-, 25-, and 100- year storm events. The runoff model enabled JNEI to perform a thorough analysis of the watershed s sensitivity and natural response to the proposed development during the various storm events. The unmitigated model also created a baseline from which to compare the response to development for individual reach segments throughout the Moore s Creek Watershed. 13