Volume Reduction of Highway Runoff in Urban Areas: Guidance Manual (2015)

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B-1 A p p e n d i x B B-1 1 Introduction and Purpose B-2 2 Intended Applications and Functionality B-2 3 General Use of Tool B-2 3.1 System Requirements B-3 3.2 Preparing the Tool for Use B-3 3.3 Starting a New Project B-4 3.4 Organization of the Tool B-5 3.5 Navigating Within the Tool B-5 3.6 Saving and Editing Scenarios B-5 3.7 Printing Summary Results B-5 4 Entering Project Location and Climate Information B-5 4.1 Selecting a Rain Gage B-6 4.2 Providing Site-Specific Precipitation Statistics B-6 5 Entering Project Design Information B-6 5.1 Entering Tributary Area Attributes B-8 5.2 Selecting VRAs and Entering VRA Design Parameters B-8 5.2.1 Entering First VRA Input Parameters B-9 5.2.2 Selecting Two VRAs in a Treatment Train B-10 6 Viewing and Interpreting Volume Performance Results B-10 6.1 Viewing Volume Performance Results B-11 6.2 Running a Sensitivity Analysis B-12 6.3 Viewing Supporting Data B-12 7 Error Messages B-13 8 Tool Theoretical Basis and Technical Assumptions 1 Introduction and Purpose The performance of volume reduction approaches (VRAs) is a function of many factors, includ- ing local climate and hydrology, storage volume, VRA design (i.e., footprint, depth, and discharge rates), and underlying soil properties. The purpose of the Volume Performance Tool is to assist in efficiently estimating the performance of volume reduction approaches and understanding the effects and sensitivity of local climate patterns, design attributes, and site conditions. The tool is a macro-enabled Excel spreadsheet application that calculates an estimate of long-term volume User’s Guide for the Volume Performance Tool

B-2 Volume Reduction of Highway Runoff in Urban Areas reduction based on user-provided location and planning-level project information. This tool is intended to allow DOT staff and contractors to quickly evaluate the relative benefits of various scenarios and assist in developing sizing criteria. The purpose of this document is to guide users through the steps and inputs necessary to provide a reliable estimate of volume reduction through BMP treatment for site-specific project requirements. In addition, the steps required to perform a sensitivity analysis and interpret the results are outlined. Additional guidance is also provided within the tool itself in the form of a Readme page and Guidance and Default Values columns. 2 Intended Applications and Functionality The tool is intended for planning-level analysis and conceptual design-level analysis of VRA designs. It is intended to assist in: • Estimating the long-term volume reduction performance of VRAs, • Understanding the effects and sensitivity of local climate patterns, design attributes, and site conditions on volume reduction performance, and • Utilizing performance feedback to select VRAs and develop sizing and design criteria to be incorporated into a detailed design process. The following general limitations are inherent in the architecture of the tool: • Each instance of the tool can be used to analyze a single drainage area (watershed) within the project. • Up to two VRAs in series (i.e., a treatment train) can be applied to the project drainage area. • The tool is considered reliable for developing sizing criteria and design parameters (e.g., total storage needed, VRA footprint needed, and drawdown time). However, the tool does not simulate detailed hydraulics of the conveyance system or the VRA outlet structure; therefore, it should be coupled with design-level analysis methods as part of developing detailed project designs. For example, the tool can be used to set a drawdown goal of 12 hours for bioretention ponding stor- age, but more detailed hydraulic calculations would be needed as part of detailed design to set the orifice size or media specifications needed to achieve this drawdown time. • The tool does not fully support VRA designs that are well outside of the typical range of VRA design parameters; in these cases, the tool will extrapolate results and may underestimate or overestimate performance. Notes appear in the tool in red text when normal operating bounds are exceeded. Please review the Readme page for further discussion of limitations and intended uses. 3 General Use of Tool 3.1 System Requirements • The tool is intended to run in Microsoft Excel 2010 or 2013; macros must be enabled for the tool to run properly. This can be adjusted in Excel settings or by clicking the message board to enable macros when the tool opens. • Excel must be set to “Automatic” calculation mode rather than “Manual” calculation mode. This can be adjusted from the “Formula” ribbon by selecting “Calculation Options.” • The tool has been tested in a Windows 7 environment; user experience may differ in other operating system environments. • Each instance of the tool requires approximately 20 MB of storage space. • The tool involves no traditional installation, and therefore should generally not require administrator privileges to use. For users operating within strict security settings, adminis- trator privileges may be required to enable macros within Excel.

User’s Guide for the Volume performance Tool B-3 3.2 Preparing the Tool for Use To save the tool files on your computer and prepare them for use, follow these steps: 1. Load the tool by accessing the CD-ROM that accompanies this manual (or the ISO image available for download from the project website) and following the commands within the installation dialogue boxes. The tool may be saved to the directory of the user’s choice (local machine or network). 2. The tool consists of one single macro-enabled spreadsheet (.xlsm) that is ready to use once it is installed (i.e., saved) on the directory of user’s choice. 3. The original .xlsm tool file is read-only; therefore, each instance of the tool must be saved as a new file name, as discussed in the following section. 3.3 Starting a New Project To start a new project, follow these steps: 1. Open the original tool spreadsheet by double-clicking the .xlsm file. 2. When the tool opens, it is necessary to enable macros. The process of enabling macros var- ies depending on local security settings in place. If macros are not enabled, the user should consult Excel support for guidance in enabling macros. 3. Save the project to a directory of the user’s choice by using the “Save As” command in Excel. The file must be saved as a macro-enabled workbook (.xlsm) file. 4. The tool will open to the Project Location worksheet. The header provides space to enter project information (see Figure 1). 5. Once the project information is entered into the heading of the Project Location worksheet, the remaining headings on subsequent worksheets will be updated to match. 6. These steps can be followed for each project/scenario being analyzed with the tool. Navigation Bar Project-specific Information Figure 1. Project information and navigation bar.

B-4 Volume Reduction of Highway Runoff in Urban Areas 3.4 Organization of the Tool The tool is divided into various input forms that reside on separate worksheets. In some cases, multiple input forms are found on a single worksheet. Table 1 summarizes the organization of the tool. Each input form contains stepwise instructions and a key to the color of cells that appear in the form. Color coding identifies cells as: • User Steps (i.e., instructions) • Headings and Descriptions • User-Entered Data • Default Data (editing allowed with rationale) • Lookup Reference and Calculation Values (not editable) • Guidance • Warnings The user is expected to enter data for each “User-Entered Data” cell at a minimum and should review the default and reference values to verify that they are appropriate. Inputs are intended to be populated sequentially (e.g., Project Location, Project Design—VRA 01, then Project Design—VRA 02). Inputs on previous tabs can later be modified by skipping backward and forward; however, skipping forward as part of the initial tool parameterization will result in an undesirable user experience and potential for calculation errors. Input Form Worksheet Name Summary of User Inputs and Results Project Location and Climate Selection Project Location Specify project location View default climate parameters Override default climate parameters as needed Tributary Area Attributes Project Design Specify tributary area characteristics View reference information related to precipitation and runoff volumes First VRA Parameters Project Design Select first VRA type Specify primary VRA design parameters View and edit default and additional design parameters Specify whether the VRA discharges to a second VRA Second VRA Parameters (optional) Project Design Select second VRA type Specify primary VRA design parameters View and edit default and additional design parameters Volume Performance Results Volume Performance Results View summary of performance results in tabular and graphical format Sensitivity Analysis Sensitivity Analysis Specify sensitivity scenarios by selecting sensitivity bounds and identifying sensitivity parameters Run analysis and view sensitivity results Supporting Data Supporting Data View underlying model results data used by the tool to provide performance estimates Table 1. Organization of the tool.

User’s Guide for the Volume performance Tool B-5 3.5 Navigating Within the Tool The tool provides two options for navigation: • The navigation bar that is located below the project information on every page (see Figure 1) provides hyperlinks to jump to each input form. These buttons can be clicked to move forward or backward to each input form. • Traditional Excel navigation methods can also be used, including selecting worksheet tabs, scrolling, and zooming, as the user prefers. Either of these methods can be used, interchangeably, at any point in use of the tool. 3.6 Saving and Editing Scenarios Each instance of the tool (i.e., each individual .xlsm file) represents a single scenario. Multiple scenarios can be run using the following general steps: 1. Open a new instance of the tool. 2. Enter inputs to define the first scenario. 3. Save this scenario with a distinct file name (e.g., “File” ➔ “Save As” ➔ “VolumeTool_ScenarioA1 .xlsm”). 4. Edit inputs to define a new scenario. 5. Save this scenario with a distinct file name (e.g., “File” ➔ “Save As” ➔ “VolumeTool_ScenarioA2 .xlsm”). Repeat for as many scenarios as desired. Files can be organized into directories to help dis- tinguish different analysis scenarios. After scenarios are generated, any of the instances of the tool can be reopened by double-clicking on the selected .xlsm file to view the scenario inputs and results. 3.7 Printing Summary Results Any sheet within the worksheet can be printed using native Excel print functions. The user can use Excel menus to specify the paper size, printer preferences, and print ranges. By selecting multiple worksheet tables, multiple worksheets can be printed at the same time. Please consult Excel documentation and help files for guidance on printing from Excel. 4 Entering Project Location and Climate Information 4.1 Selecting a Rain Gage The first step in developing a project scenario is to select the appropriate precipitation gage for your project (see Figure 2): 1. Select your project’s region by clicking on the map. 2. Select your project’s state by using the drop-down menu under “States within Selected Region.” 3. Select the precipitation gage that best represents the project precipitation by using the drop-down menu under “Rain Gages Available in State.” Generally, the precipitation gage closest to the project location should be used. Each precipitation gage has associated ET data as well.

B-6 Volume Reduction of Highway Runoff in Urban Areas 4.2 Providing Site-Specific Precipitation Statistics When a gage is selected, the tool provides a number of reference statistics related to the gage, includ- ing the 85th- and 95th-percentile, 24-hour storm depths and the average annual precipitation depth. If more accurate precipitation statistics are available for the project location, these data can be used to improve the estimates provided by the tool. The tool uses the 85th-percentile, 24-hour storm depth and the average annual precipitation depth to localize model estimates. To enter site-specific precipitation statistics, overwrite the “Project Location” values as called out in Figure 3. If a new gage is selected, user-entered numbers will be overwritten and must be entered again if still applicable. Note that default and project-specific precipitation statistics are for reference and scaling pur- poses only; they do not imply a VRA size used for performance analysis. The user enters the VRA sizing parameters to be analyzed on the Project Design worksheet. 5 Entering Project Design Information 5.1 Entering Tributary Area Attributes To determine the quantity of runoff that will drain to the VRAs in the design scenario, it is necessary to provide certain inputs regarding the tributary area watershed. Follow these steps to provide the necessary tributary area information (see Figure 4): 1. Enter the tributary area (in acres) that represents the entire area that will drain to your VRA. Except in the case of permeable pavement, the tributary area should exclude the VRA area itself. In the case of permeable pavement, the VRA should be counted as part of the tributary area with an imperviousness of 100%. 2. Enter the estimate of percent of the tributary area that is impervious (ranging from 0% to 100%), which determines the relationship between impervious and pervious area and whether the rainfall will infiltrate or run off. Permeable pavement area should be entered as 100% impervious in this input to represent the fact that all rainfall on permeable pavement enters the pavement storage reservoir (similar to runoff from 100% impervious area). Map to Select Region State Drop- Down Menu Climate Division and Rain Gage Drop-Down Menu Figure 2. Project location and climate selection layout.

User’s Guide for the Volume performance Tool B-7 Tributary area watershed parameters to update These cells are reference values that are calculated based on the user- entered tributary area parameters and the selected precipitation statistics. Figure 4. Tributary area attributes layout. 85th-percentile, 24-hour storm depths and average annual precipitation depths may be overwritten with site-specific data. Figure 3. Site-specific precipitation data.

B-8 Volume Reduction of Highway Runoff in Urban Areas 3. Select a tributary area soil type from the drop-down menu provided. These soil types have been chosen to represent the typical hydrologic soil groups (A through D). The soil type selected here should be representative of the soil beneath the tributary area. When this soil type is selected, a representative infiltration rate (based on the literature) is also copied into the “underlying soil infiltration rate” input for your VRAs. However, note that the soil type may vary between the tributary area and the VRA area, and the infiltration rate should be updated to reflect a value that is appropriate within the VRA area. This may occur when different soils are present within the VRA area than the overall tributary area or when better VRA area infiltration rate data are available, such as that obtained from field testing. It is strongly recommended that default infil- tration rate values be updated with site-specific information whenever available. 4. Review the default long-term runoff coefficient and enter a user-provided long-term runoff coefficient, if desired. Several tributary area runoff reference values are reported below the user inputs. These are for reference purposes only and are not to be confused with VRA design inputs, which are entered in the next section. 5.2 Selecting VRAs and Entering VRA Design Parameters 5.2.1 Entering First VRA Input Parameters To begin providing the inputs for your first VRA, follow these steps (see Figure 6): 1. In the “What is the first VRA type?” input, select the type of VRA that will be the first (and potentially only) VRA receiving runoff. 2. Once the type of VRA is selected, the “BMP Override” message (Figure 5) will display to remind you that you are selecting a new VRA and that it will override the existing design parameters that have been selected. If you are ready to start over or change your design, click “yes.” If you want to keep your original VRA, click “no.” 3. After the type of VRA is selected, the design parameters will need to be inputted. The blue cells are project-specific and should be updated. The yellow cells also may be project-specific; however, default values have been provided for these parameters. If the default values do not represent the project design, then they may be overwritten. 4. In addition to the “Primary Design Parameters,” some VRAs will also have additional param- eters, which are either additional input values or reference calculations (e.g., calculated draw- down time). To view and edit these parameters, select “yes” in the field entitled “Would you like to view/edit additional design and reference parameters?” Default parameters are pro- vided for these parameters; however, these should be reviewed and adjusted, as needed, to match actual project design configurations to provide the most accurate results. 5. If there is only one VRA in your design, proceed to the volume performance results after all the parameters have been updated by clicking the “Volume Performance Results” button or Figure 5. VRA selection message box.

User’s Guide for the Volume performance Tool B-9 worksheet tab. However, if there is a second VRA in your design, refer to the following section for guidance. Note: Guidance regarding the individual VRA parameters is not provided in this user’s man- ual. Please refer to the “Guidance” and “Default Value” columns located within the tool that provide guidance for each parameter specific to the VRA selected. Additionally, refer to VRA fact sheets in Appendix A for more information on VRAs and typical ranges of design parameters. 5.2.2 Selecting Two VRAs in a Treatment Train If there are two VRAs as a treatment train in your design, follow these steps: 1. Select “yes” from the field asking “Is there a second VRA in the treatment train?” or click on the “Second VRA Parameters” button and click “yes” in the window that pops up to confirm that you want to add a second VRA to your design (Figure 7). 2. Selecting “yes” will load the “User-Entered Design Parameters” for the second VRA. Follow the previous steps outlined for the first VRA (Section 5.2.1) to fill in parameters. 3. After all of the parameters are entered for the second VRA, proceed to the volume perfor- mance results to evaluate the performance of the design. Note that volume reduction estimates are provided below the primary design parameters in the “First VRA Parameters” and “Second VRA Parameters” sections for reference. These results are intended to help facilitate rapid evaluation of multiple scenarios. Figure 6. First VRA parameters input form layout. “User-Entered Design Parameters” to be updated Guidance column to help users select the appropriate inputs for their designs Selection to edit default parameters if desired SCM-type drop-down menu Figure 7. Second VRA message box.

B-10 Volume Reduction of Highway Runoff in Urban Areas 6 Viewing and Interpreting Volume Performance Results 6.1 Viewing Volume Performance Results The Volume Performance Results worksheet is updated based on the scenario that has been inputted in previous forms. It is designed to be printed on a single page to document key inputs as well as results. The Volume Performance Results page consists of the following two sections: 1. A summary of your design, and 2. A tabular and graphical volume performance summary for your design. The first part of the sheet (Figure 8) summary section provides a concise description of your VRA or VRA treatment train and the key conceptual design parameters. The volume performance summary, located below the input summary on the same worksheet, provides a tabular and graphical representation of the estimated volume reduction achieved by your design. These results are reflective of the cumulative performance provided by the VRA(s) provided in the Project Design worksheet. The following results are provided within this summary: • Baseline Average Annual Runoff Volume. This value represents the estimated average annual volume runoff for the tributary area to the VRA(s), based on climatic region/sub-region, drainage area, imperviousness, and soil type. Figure 8. Volume performance summary—echo of scenario inputs.

User’s Guide for the Volume performance Tool B-11 • Reduction in Runoff Volume. This value represents the predicted average annual volume reduction achieved by the VRAs given the inputs provided. This volume represents the total reduction of volume from ET and infiltration, if they are applicable to your chosen design. • Captured, Treated, and Released Volume. This value represents the predicted average annual runoff volume captured by the VRA(s) that is treated and then released back into the envi- ronment. This volume is a separate calculation from and does not include the volume that is reduced via ET or infiltration. • Runoff Bypassed Volume. This value represents the estimated annual volume bypassing or overflowing the VRA(s). Each value is expressed in terms of an average annual runoff volume (ft3/year) as well as a percentage of the baseline runoff volume. A pie chart illustrates the relative proportion of each element (Figure 9). 6.2 Running a Sensitivity Analysis A sensitivity analysis allows the user to vary VRA design parameters and observe how this variation affects the final volume reduction estimates. The user is able to analyze a low and high bound value of design parameters by selecting a low and high multiplier that will adjust the already established design value for each parameter selected. Navigate to the “Sensitivity Analysis” page by clicking the “Sensitivity Analysis” button or worksheet tab and follow these steps to perform the sensitivity analysis for your design: 1. Enter the value for the “High Multiplier.” This value will be multiplied by the design value for each parameter selected for analysis and represents the high bound. 2. Enter the value for the “Low Multiplier.” This value will be multiplied by the design value for each parameter selected for analysis and represents the low bound. 3. Select the design parameters to be analyzed for the first VRA from the drop-down menus provided. 4. If your design is a treatment train with two VRAs, select the parameters to be analyzed for the second VRA from the drop-down menus provided. (This will not be shown if two VRAs are not part of your design.) Note: When a new VRA is selected, the user must reselect the Figure 9. Volume performance tabular and graphical results.

B-12 Volume Reduction of Highway Runoff in Urban Areas sensitivity parameters from the drop-down menu to ensure that the parameters being ana- lyzed are applicable to the current design and VRA. 5. Click the “Run Sensitivity Analysis” button. See Figure 10 for an example of inputs to the sensitivity analysis. The results of the sensitivity analysis are presented in tabular and graphical form. Each sensi- tivity scenario represents the resulting performance if all other parameters are held fixed and the selected parameter is varied between the low and high bound. For each parameter analyzed, the low bound, design, and high bound estimates for volume reduction are displayed. If the design consists of a treatment train with two VRAs, the calculated results are representative of the total treatment train performance. An example of sensitivity analysis results is provided in Figure 11. 6.3 Viewing Supporting Data The Supporting Data worksheet provides selected plots showing the continuous simulation model results that are being referenced by the tool to provide the VRA-specific performance results. The information on this worksheet is not editable and is provided for informational and technical documentation purposes only. 7 Error Messages The tool provides volume reduction estimates by referencing tens of thousands of hydrologic simulations. Because an individual simulation is not being run for each individual project, the tool has some inherent limitations. When providing inputs, the tool interprets them and returns values based on a specific range of data. If the user-provided data are outside of this range, the tool will override the user input with the minimum and maximum values, respectively. In the event that this occurs, the tool will likely be underestimating performance if forced to use Figure 10. Sensitivity analysis inputs.

User’s Guide for the Volume performance Tool B-13 the maximum value or overestimating performance if forced to use the minimum value. If the input bounds are exceeded and the minimum or maximum is used, an error message will be displayed for the applicable VRA, similar to that shown in Figure 12. The user should review the error message and adjust inputs or interpret results accordingly. A key to help understand error messages is provided in the Readme page of the tool. 8 Tool Theoretical Basis and Technical Assumptions This tool is based on a number of technical assumptions. These assumptions are not critical for general use of the tool; however, they may be relevant for interpreting results and understanding the limits of the applicability of the tool. For detailed information about the theoretical basis for the tool and the underlying technical assumptions, see Annex A: Technical Documentation of Volume Reduction of Highway Runoff in Urban Areas: Final Report, which is part of NCHRP Web- Only Document 209. Figure 11. Sensitivity analysis results.

B-14 Volume Reduction of Highway Runoff in Urban Areas Example error message notifying user of input data outside of lookup bounds Figure 12. Error message (shown in red).