MS4: MAPPING CHALLENGES. Mike Towle Associate Planner, WestCOG

Size: px

Start display at page:

Download "MS4: MAPPING CHALLENGES. Mike Towle Associate Planner, WestCOG"

Jane Wilcox
5 years ago
Views:

MS4: MAPPING CHALLENGES Mike Towle Associate Planner, WestCOG mtowle@westcog.

1 MS4: MAPPING CHALLENGES Mike Towle Associate Planner, WestCOG Please contact or attribute author before using any images or data from this presentation

2 Overview I. Theory and background II. Mapping Requirements III. Mapping Challenges Caveats: Do not represent CT DEEP Focus on overview of processes and pitfalls Not a discussion on BMPs 2

3 I. THEORY AND BACKGROUND 3

4 The new MS4 Permit requires mapping Mapping of Stormwater Infrastructure Mapping DCIA 4

5 Where? 5

6 What is Land Cover? Found at UCONN CLEAR website: 6

7 What is Impervious Cover Found at Bing Maps: 7

8 IC greater than 11% impairs watersheds 8

9 Alternative: Directly Connected Impervious Areas (DCIA) Utilized in this permit! 9

10 Connected Roof (DCIA) 10

11 Disconnected roof 11

12 Which IC areas are connected and which are not? 12

13 Road Connection Types Connected (Curb and gutter): Unconnected Ambiguous 13

14 II. MAPPING REQUIREMENTS 14

15 Required Stormwater Infrastructure Need to have a model of stormwater infrastructure Inventory of all outfalls Implies WATERSHEDS! (including outside of your own town) Other required mapping elements ( pg 3 Appendix) Outfalls and receiving waters Pipes Open channel conveyances Catch basins Manholes Interconnections Stormwater treatment SS and combined (if available) 15

16 DCIA Base Line Mapping Outfalls Outfall catchment areas Impervious area in catchment areas DCIA in catchment areas Inventory and mapping of discharges shall be completed within two (old) or three (new) years Determine which watersheds are DCIA>11% Determine priority watersheds 16

17 Mapping DCIA Elimination Reduce by 1% a year Starting in 4 th year Can count previous reductions 17

18 III. MAPPING CHALLENGES. 18

19 Mapping Challenges Mapping infrastructure DCIA Baseline Mapping Find Outfalls Delineating catchment areas for outfalls Determining DCIA within catchment area Unclear guidance 19

20 DCIA Base Line Process Step 1: ID Outfalls Find each outfall Part of collecting stormwater infrastructure data Requires field verifications, imagery, and CAD drawings 20

Step 2: Determine Watersheds and Catchments Areas for Each Outfall Alternative 1 (area impacts results) Acquire watershed areas and geometry from DEEP website http://cteco.uconn.

21 Step 2: Determine Watersheds and Catchments Areas for Each Outfall Alternative 1 (area impacts results) Acquire watershed areas and geometry from DEEP website Problems: Old data set (1980s, 10 ft contours) Poor resolution (1:24000) Does not account for urban drainage complexity (multiple outfalls, errors, more outfalls than watersheds) Not one outfall to one watershed 21

22 Example Issue: 800+ outfalls >>local basins 22

23 Step 2: Determine Watersheds and Catchments Areas for Baseline Alternative 2 Create Your own catchments! Field inspection Semi-automated GIS tools Problems: Labor intensive Skill intensive Dependent on quality of DEM (available) Does not account for 3d elements such as rooftops 23

24 Example of WS Creation 24

25 Step 3: Determine DCIA within catchment area Permit provides two recommended choices Single parameter Sutherland Method 25

26 Step 3: Determine DCIA, Sutherland equation Combines land use and stormwater infrastructure Select category Apply to watershed No guidance for watershed size but presumably roughly equivalent to local basin 26

27 Step 3, Alternative Field Method with Sampling (Untested) Identify the different combinations of impervious cover. Examples: Driveways Drains towards or away from street` Roads Guttered or not Advantage: Need planimetrics with attributes but can assign values at sit Cheaper and easier than field inspections Sample each (30 to 50) Create representative values for each type 27

28 Field Verification 28

29 Step 4 Final Processing Simple aggregation and counting But, need to track changes within each outfall catchment (logistical challenge) 29

30 Conclusions Logistical challenge to coordinate efforts. Mapping requirements and methods are still being determined Get best possible IC, preferably with attributes Budget for field verification of watershed 30

31 Questions??? Contact Info Mike Towle Associate Planner, WestCOG Carl Zimmerman, PhD Senior GIS Manager, WestCOG 31

32 REFERENCES 32

33 General Guidelines Different mapping and monitoring references in permit See UCONN CLEAR doc Many guidelines in Appendix B A couple of proposed models to determine DCIA% But No guidance on watershed boundaries No guidance on scale The DCIA calculations shall be based on criteria available through the DEEP stormwater page pg. 30 of permit 33

34 General Guidelines Inventory and mapping of discharges shall be completed within two (old) or three (new) years Pg. 43 Determine which watersheds are DCIA>11% Determine priority watersheds In years 4 and 5 of permit demonstrate 1% reduction per year 34

35 Step 2: Determine Watersheds and Catchments Areas for Baseline Steps in Spatial Analyst>Hydrology Acquire/create high resolution DEM Resolve locations such as bridges or artificial barriers that impede Remove sinks using Fill tool Run Flow Direction Tool Run Flow Accumulation Tool Input FD and FA into Watershed Tool Identify pour point(s) and run 35

36 DATA REQUIREMENTS 36

37 Available Data Sets From State Imagery 2016 Sanborn flight (3 4-band) Allows you to see infrastructure Topography LiDAR and 1m DEM Allows you to model flow across landscape to inlets or receiving waters Road centerlines (for public entities only) Allows you to determine major contributors of DCIA 37

38 Available Data Sets From State IC m IC raster from DEEP Provides baseline data with simple aggregation NO ATTRIBUTE INFORMATION Watershed and Drainages from DEEP Impaired water identification 38

39 Very Useful Data Sets!!!! IC: Planimetrics Roads, streets, sidewalks, etc. Has attributes! Watershed and Catchment lines FOR OUTFALLS that account for urban drainage complexity Curb and gutter locations 39

40 Critical Issues: Getting Best Possible IC Data and WS Highest resolution Not 30m Preferably not raster Includes attribute information about IC type 40

41 Rules of Thumb: Connected Versus Disconnected Connected Curb and gutter roads are connected Parking lots with inlets and commercial parking lots are connected Big commercial buildings are connected Driveways above grade of road centerline Disconnected Residential bldgs. below street grade are unconnected Crowned rural roads are unconnected (no curb and gutter) Residential roof tops in lower density neighborhoods are disconnected 41

42 Primary Sources of DCIA in the Landscape Transportation infrastructure Curb and gutter streets Driveways and parking with inlets and drains Rooftops Commercial bldgs Higher density residential with shorter driveways Commercial areas 42

43 References Zimmerman, C Determining Directlty-connected Impervious Areas in Residential Land Uses. Unpublished dissertation. Found at UCONN Digital Commons. 43

44 Annotated References 44

45 Annotated References 45

Urban Mapping and Providing Partner Services Utilizing GIS Presenter: Josh Garver. GISP, Assistant Director;

Urban Mapping and Providing Partner Services Utilizing GIS Presenter: Josh Garver. GISP, Assistant Director; jgarver@franklinswcd.org What I d Like You to do: Think Spatially Look for Shapes Look for Patterns