Stormwater Final Draft

January 20, 2005

The report describes an effort that began in March 2004 to create a shared vision with concerned residents and elected officials as to what solutions are needed to relieve the flooding problems that have faced the town for generations.  More importantly, the report provides a “road map” for how to successfully improve drainage throughout the Town of Round Hill in the years to come.


Early last year, the Town of Round Hill adopted a streetscape master plan, which established the new minimum standard for your roadways; to include improved sidewalks, traffic calming, and roadside beautification strategies through landscaping.  The streetscape master plan also identified the need for a storm water master plan to address drainage problems in the town.

Round Hill has a system of roadways that lack adequate drainage capacity.  Some runoff flows down sidewalks, across roadways and into yards and basements.  Other runoff simply stands along the edge of pavement in localized depressions.  These problems occur even though the Town of Round Hill has sloping terrain and is surrounded by naturally preserved waterways with good capacity for storm water runoff.

This report has been developed to describe drainage problems through a project formulation, compare alternative solutions, and make recommendations in the sections of the report that follow.

Project Formulation:

The first step in master planning was to develop base mapping of the town.  For this purpose, we obtained Loudon County GIS data and coverages that include buildings, topography, land cover, streams, floodplains, parcels and other relevant information.  We then

prepared base mapping on a “watershed basis”, meaning that the study area was extended to high points and low points in the terrain just beyond the Town’s municipal boundaries.  Mapping was then converted to AutoCAD format for use in this study. This existing conditions map of the town is enclosed as Exhibit A.

The second step in project formulation was to distribute a survey to town residents that was designed to solicit input on known drainage problems.  Surveys that were returned to the Town have been included in Appendix A.

As surveys were received, the opportunity to provide comments directly to our engineering team was also provided through an informal town meeting, held on April 28, 2004.  Several residents took this opportunity to describe drainage problems, and to provide additional survey responses, which are also included in Appendix A.

As a follow up to the town hall meeting, a field review was conducted on April 29, 2004.  Town residents helped the engineering team locate identified drainage problems, obtain additional field data, and further document the condition of the town’s drainage systems.

Survey responses, discussions with town residents, field reports, and mapping were then used to develop a plan showing identified drainage problems.  This is included as Exhibit B of this report.  Problems have been grouped and described in basic terms on this exhibit in order to provide an overview of the identified areas of concern.  It is important to note, however, that more detailed field notes and photographs are being kept and developed into the solutions that will follow.

Alternative Analysis:

Based on the coordination and determination of drainage problems, some general guidelines governing the selection of solutions were established.

  • The large response to the survey and town meeting indicate that drainage problems are a significant concern by town residents and that the problems are widespread;
  • All identified drainage problems should be addressed in the master plan we develop, but choosing cost effective solutions and prioritizing improvements will help address the limited funding that is available;
  • Environmental impacts will need to be addressed; and
  • The solutions will not include storm water detention because open space has not been designated in land use plans for the construction of detention basins in the town, and because the anticipated pipe sizing is relatively small.  If ponds or dry basins are built with developer projects, this will offset potential increases in peak discharge and will be consistent with this master plan.

With these initial guidelines in mind, we developed a preliminary engineering analysis of the identified drainage problems as follows:

Hydrology:  Using topographic mapping, the town was broken into watershed areas that create concentrated discharge at 9 primary locations under existing conditions (a map showing the drainage basins is included in Appendix B).  Some small areas of sheet flow were outside of the areas with identified drainage problems and were not evaluated.  Within these primary drainage areas identified, watershed response time was then measured in a “time of concentration” and watershed land uses were evaluated to determine a “c-factor”.  These hydrology factors were then used to determine peak discharge estimates based on the “modified rational equation”.  The supporting hydrology calculations are included in Appendix B.

Hydraulics:  Hydraulic calculations for sizing pipes were based entirely on the continuity equation (Q=AV) and the assumption that the velocity of discharge through the pipes for a 10-year storm event will average at least 4 feet per second (fps) due to sloping terrain. 3fps is the minimum velocity desired for pipes to be “self-cleaning”, meaning that larger storm events will cause sediment deposited in the pipes to wash away. In reality, the sloping terrain in Round Hill will probably allow flow velocities to be higher and pipe sizing in some areas to be slightly smaller than indicated in this master plan.

Budget:  Pipe and ditch lengths were measured from the alternative solution plans, included as exhibits to this report.  These measurements are approximate and are only provided as a basis for cost estimating.  Cost estimating is also approximate and was determined as follows:

  1. Pipe Cost = Avg. Pipe Size x $2 per inch diameter x Pipe Length
  2. Ditch Cost = Equivalent Pipe Cost / 3
  3. Inlets and Incidentals = Additional 30% of the Pipe & Ditch Costs

Other costs for engineering design, drainage easements, utility conflicts, and other potential aspects of the drainage improvement projects will need to be treated as additional costs when determining the final budgetary needs for each solution.  Costs for street improvements such as paving, curbing, lighting, utilities, landscaping and beautification are not included in these budgetary estimates, but could cost three to five times as much as the related drainage improvements considered in this study.  This should be considered if the town decides to package drainage improvements with streetscape improvements.

Alternative Solutions:

Based on our analysis, we have developed three (3) plans showing alternative drainage solutions.  Each plan is based on the hydrology calculations in Appendix B and the hydraulics and cost estimating methods described above.  The following tables summarize the results for each alternative and should be used along with map exhibits for comparison.

Table 1 – “High End” Solution (Exhibit C)

The goal of this plan is to provide closed storm drainage systems that can be incorporated into streetscape improvements throughout the town, to achieve a “high end” solution for addressing drainage problems in the Town of Round Hill.

Location IDFlow (Q10)Range of Pipe SizesPipe LengthsDitch LengthsBudget
112 cfs18″ – 24″790 ft180 ft$46,000
234 cfs15″ – 42″2,260 ft0 ft$167,000
330 cfs15″ – 36″1,400 ft120 ft$95,000
422 cfs15″ – 30″3,790 ft0 ft$222,000
526 cfs15″ – 36″1,500 ft0 ft$100,000
621 cfs18″ – 30″2,360 ft0 ft$147,000
710 cfs18” – 24”240 ft550 ft$23,000
817 cfs18″ – 30″580 ft0 ft$36,000
95 cfs15” – 18”560 ft0 ft$24,000

Table 2 – “Low End” Solution (Exhibit D)

The goal of this plan is to provide a “low end” solution through the use of open ditches, which reduces the funding needs for drainage improvements to a minimum, while still addressing the drainage problems in the Town of Round Hill.

Location IDFlow (Q10)Range of Pipe SizesPipe LengthsDitch LengthsBudget
112 cfs18″ – 24″320 ft630 ft$29,000
234 cfs15″ – 42″770 ft1,400 ft$92,000
330 cfs15″ – 36″90 ft1,100 ft$30,000
422 cfs15″ – 30″3,460 ft80 ft$204,000
526 cfs15″ – 36″500 ft380 ft$42,000
621 cfs18″ – 30″1,810 ft550 ft$124,000
710 cfs18” – 24”40 ft740 ft$12,000
817 cfs18″ – 30″420 ft130 ft$29,000
95 cfs15” – 18”120 ft450 ft$12,000
In comparing these first two alternative solutions for “high end” and “low end” performance and in looking at developing a recommended plan that provides a compromise solution, the following factors were considered:
  • Alternative solutions involving the use of open ditches will be helpful in reducing project costs where the Town of Round Hill does not anticipate streetscape improvements and where open ditches are acceptable to impacted residents;
  • Alternative solutions involving the use of existing pipes will be helpful where a cost savings can be achieved and where the existing pipes are adequately sized and determined to be in good condition; and
  • · Alternative solutions involving a diversion of runoff will be helpful where a cost savings can be achieved without creating downstream drainage problems and where acceptable to impacted residents.

With these factors in mind, a compromise solution was developed with a “best value” approach.  A “best value” approach is defined as a qualitative comparison of the benefits to reducing drainage problems, the costs (both construction and long term maintenance) and the expectations of town residents determined through project consensus building efforts.  This compromise solution was developed through several iterations designed based on input from town residents and elected officials.  Consensus building efforts included posting the plan on the town’s website, hosting a second public meeting to present solutions on July 29, 2004, and follow-up field review on July 30, 2004.

Table 3 – Compromise Solution (Exhibit E)

The goal of this plan is to provide a “best value” solution.  This solution will be refined in developing the final master plan to follow.

Location IDFlow (Q10)Range of Pipe SizesPipe LengthsDitch LengthsBudget Remarks
112 cfs18″ – 24″635 ft415 ft$42,000Use 250’ open ditch to save $5,000
234 cfs15″ – 42″1,770 ft490 ft$143,000Use 490’ open ditch to save $12,000
330 cfs15″ – 36″1,150 ft370 ft$84,000Use 370’ open ditch to save $8,000
422 cfs15″ – 30″3,550 ft0 ft$208,000Use 260′ of existing pipe to save $15,000 at post office/fire station
526 cfs15″ – 36″1,070 ft0 ft$71,000Divert at 17 New Cut Road to reduce pipe length by 450′ & save $30,000.
621 cfs18″ – 30″2,380 ft0 ft$149,000No savings planned.
710 cfs18” – 24”40 ft820 ft$17,000Use 690’ open ditch to save $12,000
817 cfs18″ – 30″400 ft130 ft$27,000Use 120’ open ditch to save $3,000
95 cfs15” – 18”560 ft0 ft$24,000No savings planned.

Recommended Plan:

Having developed the compromise solution as a recommended plan of action through a comparison of alternatives (see previous section of this report), it was clear that funding is not readily available to construct all of the necessary drainage improvements in the Town of Round Hill.  Since August 2004, the recommended plan has been refined through council presentations and continued discussions with town staff to include a more detailed breakdown of prioritized improvements and implementation strategies, based on the following factors:

  • Drainage improvements that can be built, even as temporary measures, through negotiations with developers (or through proffers) will be given a high priority since they will help meet a public need without requiring public funds;
  • Drainage improvements will be broken into phases where it allows construction to proceed more quickly.  For example, open ditches and driveway culverts can be built as a temporary solution in areas where closed storm drainage improvements are not funded.  Some of these temporary improvements can be presented to the Virginia DOT as possible maintenance projects; and
  • By combining drainage improvements with streetscape improvements, the collective development needs can be addressed at one time, ultimately saving overall project cost in these areas.  Additionally, streetscape solutions that include drainage improvements may be eligible for grant funding through the Virginia DOT’s Transportation Enhancement Program (with a 20% local match).

With these factors in mind, the solutions to the drainage problems have been further studied and detailed as phased and prioritized improvements as shown on Exhibit F, with a priority ranking order as shown below:

Remedial Action Plan – The remedial action plan is designed to prioritize projects with possible funding sources that can be explored immediately through coordination efforts and the adoption of this master plan. Improvements are also grouped into this plan to provide some benefit to all of the areas identified with drainage problems in the town.  These solutions are shown in “red” on the master plan.

Stormwater Master Plan – The solutions shown in “purple” designate areas where additional drainage improvements, beyond the remedial action plan, are ultimately sought by the town.  In these cases, however, funding sources are not clearly identified and many of these improvements are not likely to be addressed immediately.  Some of these improvements may also become unnecessary if the remedial action plan is built, and the drainage problems are reduced significantly or eliminated.

Environmental Plan – One of the goals of this recommended plan is to recognize opportunities to incorporate environmental stormwater solutions into the master plan. The plan shown on Exhibit F does this through the following strategies:

  • The benefits of the naturally preserved floodplains surrounding the Town of Round Hill are maximized in this master plan since storm drainage and ditch improvements are almost entirely being constructed outside of the floodplain.

In many cases, the storm drainage systems are “daylighted” above the floodplains, which allows the ditch conveyance system to mitigate the affects of conveying stormwater runoff in pipes as follows:

  • By “daylighting” piped runoff in a ditch and using dumped rock riprap at the pipe outlet, the stormwater can be returned to a more natural condition in a ditch system;
  • By using rock weirs, rock ditch linings or concrete structures in sections of the ditch, you can reduce the need for dumped rock at the pipe outlets, raise the dissolved oxygen content in the water, and further improve the water quality in the stormwater runoff; and
  • By incorporating other stream construction materials such as root balls and vegetative plantings, you can replicate natural channel conditions in the ditches, and improve the ecological and biological benefits of the project.
  • By combining these environmental solutions appropriately in ditches you can create a more environmentally friendly natural system to mitigate erosion potential caused by the increased velocity of runoff in a storm drainage system.
  • In addition, developers and existing residents can be encouraged to use low impact development (LID) solutions when doing construction work on their property.   This could include rain gardens that trap water and infiltrate into the ground and minimizing the amount of paved surfaces.

With these recommendations in mind, a master plan (Exhibit F) is included with prioritized improvements that match the estimated construction costs in the table that follows.

StepLocation IDPipe LengthsDitch LengthsBudgetRemarks
142,340 ft0 ft$109,512Install Loudoun Street curbing and storm drainage on both sides (East of Main Street) and tie into existing pipes on Main Street as part of the TEA-21 funded Franklin Park Trail Improvements being designed as a county administered project.
26600 ft600 ft$62,400Build a temporary ditch along Loudoun Street (North Side) from Locust Street to Mystic Lane as a VDOT maintenance project.
331,280 ft1,120 ft$154,752Build storm drainage on Mulberry and ditches on N. Bridge Streets as a VDOT maintenance project and seek developer assistance on N. Bridge Street with the outfall ditch.
45320 ft0 ft$19,968Build storm drainage and a trail connection to replace the existing ditch behind 17 New Cut and obtain drainage easements.
52640 ft1,520 ft$89,440Build ditches on Main, Cedar and N. Bridge Streets and clean out existing pipes as a VDOT maintenance project.  Install a new outlet of ditches and culverts from Main Street to North Bridge Street.
61255 ft415 ft$30,680Build ditches and storm drainage at the Hampton Road / Main Street intersection (tie into and clean existing pipes) and build an outfall ditch as a VDOT maintenance project.  Also obtain a drainage easement from Mr. Albright.
7740 ft760 ft$13,728Incorporate ditches and storm drainage into the developer improvements that are planned for the Webster Property.
88400 ft130 ft$27,664Incorporate ditches, curbing and storm drainage into the developer improvements that are planned for Walraven Street.
StepLocation IDPipe LengthsDitch LengthsBudgetRemarks
941,180 ft0 ft$46,446Install storm drainage and curbing on Main and Loudoun Streets (just beyond the Main/Loudoun intersection) and tie into the previous storm drainage improvements on Loudoun Street.
1061,100 ft0 ft$51,480Install storm drainage and curbing on Church and Locust Streets and tie into the previous storm drainage improvements.  Seek assistance from Round Hill Methodist Church.
1121,130 ft0 ft$88,140Install storm drainage and curbing on Main Street.  Install storm drainage in place of open ditches for the new outlet from Main Street to N. Bridge Street
125720 ft0 ft$56,160Install storm drainage and curbing on New Cut Road and tie into the previously completed storm drainage improvements at 17 New Cut Road.
131350 ft0 ft$27,300Install storm drainage and curbing on Main Street and tie into previously completed ditch outfall.
149560 ft0 ft$43,680Install storm drainage and curbing on Main Street and seek assistance from Richmond American Homes.
156300 ft0 ft$14,040Install storm drainage and curbing on Loudoun Street and tie into previous storm drainage improvements.  Seek assistance from Round Hill Methodist Church.