City of Bonita Springs BMP Assessment Tool

Transcription

1 City of Bonita Springs BMP Assessment Tool Presented by: Matt Feeney, P.E. (City of Bonita Springs) Stephen Bourne, P.E. (Atkins) Florida Stormwater Association Annual Conference June,

2 BMP Assessment Tool (BAT) Objective Tool that estimates pollutant levels throughout stormwater system under different BMP Scenarios City of Bonita Springs, Florida 2

3 Basic Procedure for Estimating System-wide Stormwater Pollutant Regulated by Florida Dept. of Env. Protection (FLDEP) 2010 Stormwater Rule 1. Estimate runoff from sub-basins 2. Estimate pollutant within sub-basin Runoff 2a. Reduce sub-basin pollutant where BMPs are installed in sub-basin. 3. Route pollutant through system 3a. Reduce conveyance pollutant where BMPs are installed in conveyance. 3

4 Basin 14 Estimating Runoff from a Basin LU1 LU2 LU3 1. For each land use (LU) 1. Evaluate Composite Curve Number (ie over all soil types) 2. Evaluate DCIA (directly connected impervious area) for each Landuse Type 3. C = lookup(composite CN and DCIA) 4. Runoff = Area * C * Rain (Avg. Ann) 5. Evaluate total nitrogen (TN) and total phosphorus (TP) pollutant using literature conversion factors (eg. single fam residential, TN = 1.5 mg/l ) 2. Basin runoff = Sum(LU Runoff) 3. Basin pollutant = Sum(LU Pollutant) S1 S2 S3 4

5 Handling DCIA Traditionally a property of landuse We wanted more accuracy, so we virtualized it. Landuse Parcels Virtualization Algorithm Roads City Property DB 5

6 Handling BMPs Two types of BMP Reduces Pollutant arriving at this basin node. 1. BMPs that reduce pollutant flowing to a basin node. BMPShed Required Eg. Pervious Pavement 2. BMPs that reduce pollutant in a link. No BMP Shed Eg. Detention Basin, Swale Basin A Detention basin. Reduces Pollutant in this link. The BMP Shed BMP actually affects this area All BMPs will have an affected BMPShed. BMPs need to be drawn to reflect the BMPShed, not just the BMP itself. So, we ll have to ask the user to sketch out the BMP itself, plus the BMPShed. Proposed New Pervious Pavement Basin A 6

7 Inserting DCIA and BMPs into Pollutant Estimation Basin 14 LU1 LU2 Calculate using a grid approach DCIA affects only the grid cells the impervious area overlies Pollutant is reduced only within BMP Shed. LU3 DCIA BMPShed S1 S2 S3 7

8 BMP Assessment Tool (BAT) Screen Shots Tool installs as a Table of Contents View in Esri ArcMap The main control is a tab that contains Scenario Modeler, Scenario Comparison, and Settings Tabs. 8

9 BMP Assessment Tool (BAT) Screen Shots (cont) The Scenario Modeler tab is used to create and work with scenarios, and to run the runoff and pollutant loading evaluation models. The layers and lookup tables required in the scenario database are listed here. The tools for evaluating pollutant and looking at results are here. The process for evaluating pollutant levels is a two-step process. First the runoff and pollutant from each basin is evaluated. Second, the pollutant is routed downstream through the link-node network. These radio buttons allow users to switch which results are being visualized on the map. If the user clicks Nitrogen, for example, all nodes are sized and colored according to the Total Nitrogen level at the node, and all basins are colored according to their Total Nitrogen Level. N-Normalized means the basin Total Nitrogen is divided by the basin area. 9

10 BMP Assessment Tool (BAT) Screen Shots (cont) Adding BMPs is done through the BMP tab in the Scenario Modeler tab. To add a BMP, the user must activate the polygon sketch tool using the Add BMP button. Then, the user must draw the BMP polygon on the map. When the user has completed drawing the BMP (see the orange polygon in the map), the BMP table is updated with the BMP Properties. The TN Efficiency and TP Efficiency are set by default to 85% (ie. 85% of pollutant is removed by the BMP). The BMP can either affect a Link or a Node. BMPs that affect links reduce the pollutant flowing through the link by the designated efficiency percentage. BMPs that affect nodes reduce pollutant coming from a basin that drains to the affected node. For these BMPs, the user is required to draw a BMPShed, which defines the area of land within the basin that the BMP affects. 10

11 BMP Assessment Tool (BAT) Screen Shots (cont) BMPs with affected nodes (as opposed to links) must have a BMP Shed defined. A BMP (orange) with a BMP Shed (brown). The user must draw both the BMP and the BMP Shed, and associate the BMP with the node (see node selected) that represents the outlet of the basin. With a BMP Shed defined, the tool only applies the BMP s reduction rate to the area covered by the BMP Shed. 11

12 BMP Assessment Tool (BAT) Screen Shots (cont) Step 3 in the modeling processing is running the pollutant evaluation algorithm, which is a two step process. The first step evaluates the runoff from each basin, and then evaluates the pollutant contained in the runoff. This step applies any pollutant reduction from BMPs that affect nodes. The second step routes the pollutant through the link node network, applying any pollutant reduction from BMPs that affect links. The algorithm is described in the white paper attached as an appendix to this document. Since this process takes a while to complete (especially step 1), liberal feedback is provided to the user to inform them of progress, including a two progress bar display to show subtask and overall progress. 12/1/

13 BMP Assessment Tool (BAT) Screen Shots (cont) When the pollutant evaluation process is complete, the results are visualized on the map in the form of sizing and coloring the nodes and coloring the basins. The legends that specify the coloring and sizing for the node and basin layers are contained within a legends directory stored in the exectuable directory usually at C:\Program Files (x86)\bat\legends. The legends can be customized at any time as long as the final legend is saved to this directory. 13

14 BMP Assessment Tool (BAT) Screen Shots (cont) To compare two scenarios, click the refresh scenarios list button to show all available scenarios. Set one scenario as Future and one as Existing. Click the open button to open the scenarios and prepare them for comparison. Select a variable to compare from the list of variables, which include Total Nitrogen, Nitrogen Reduction Percentage, Total Phosphorus, and Phosphorus Reduction Percentage. Then click Calculate Difference to find the difference in the variable at each node. The results are added to the Node layer in the Future scenario s database. To get Node-level results, click the Select Node on Map button and then select any node in the system. The chart compares the TN and TP values at that node for each scenario. Here, we see that the Future Scenario (TestScenario), which added several large BMPs reduces pollutant significantly compared to the Existing Scenario. 14

15 BMP Assessment Tool (BAT) Screen Shots (cont) The settings tab specifies the path for the four databases of record, which contain the GIS layers and lookup tables required to build a scenario database. The user can specify a different database than the default using the folder browser buttons. The verification button checks that all the geodatabase are at the paths specified, that the required layers are in the geodatabases, and that the required fields are within the layers. The tool reports back any problems to the user as the checks proceed. The default paths are stored in a file called GDBDefaultPaths.txt in the executable directory for the tool usually at C:\Program Files (x86)\bat\gdbdefaultpaths.txt. The user can change these paths by editing the text file. 15

16 BAT System Architecture BAT System Architecture BAT (Esri ArcMap 10.1 Extension) Executable Directory Typically at C:\Program Files (x86)\bat City ICPR DCIA BMP Lookup Scenarios Directory Stores all generated scenario databases. Scenario Scenario 1 1 GDBDefaults.txt Specifies default paths for Databases of Record and Scenarios Directory. Legends Stores legend (.lyr) files that give symbology for GIS layers. Databases of Record Store Official City GIS layers and FLDEP lookup tables for pollutant calculations. 16

17 Next Steps Calibration With Existing Historic Samples Adjust Landuse to existing condition instead of ultimate build out Add New Instrumentation BMP Planning and Management Identify Key spots for BMPs Identify ideal BMP Types 17

18 More info, and Questions Contact: Matt Feeney Steve Bourne 18