Urban Erosion Potential Risk Mapping with GIS

Transcription

1 Urban Erosion Potential Risk Mapping with GIS ESRI Water Conference San Diego, CA Jan 29-Feb 1, 2018 Dr. Randy Dymond, PE, F.ASCE, D.WRE Co-investigators: Amanda Weikmann, MS Student Dr. Clay Hodges, PE Research Asst Prof

2 OUTLINE 1.Introduction 2.Methods 3.Results The Nation that destroys its soil destroys itself Franklin D. Roosevelt, Conclusion 2

3 HISTORY OF SEDIMENT REGULATIONS Soil Erosion Service (SES) Then SCS, NRCS The Federal Water Pollution Control Act The Clean Water Act (CWA) The Water Quality Act (WQA) Virginia Soil & Conservation District Law Maryland Sediment Control Regulations Maryland Sediment Control Law Virginia Erosion & Sediment Control Law (VESCL) 3

4 SEDIMENTATION AND EROSION Deposition Alter channel dimensions Landlock ports Smother aquatic organisms Deposit bound pollutants Suspension Alters aesthetics (turbidity) Blocks sunlight in water column Transport bound pollutants 4

5 STORMWATER RUNOFF REGULATIONS & CONTROL He, J. (2017). Sedimentation [Lecture notes]. Retrieved from

6 SOIL EROSION PROCESSES Transport Erosion Splash Erosion 6

7 SOIL EROSION PROCESSES Transport Erosion Sheet Erosion Rill Erosion Splash Erosion NRCS LG.jpg 7

8 SOIL EROSION MODELS Erosion Map output from USLE Erosion Map output from LISEM Figure from Mattheus et al., 2013 USLE (Wischmeier and Smith, 1978) Figure from DeRoo et al., 1994 LISEM (DeRoo et al., 1994) 8

9 OBJECTIVES 1. Investigate the important parameters of soil erosion 2. Develop a method for determining Erosion Potential (EP) through GIS and computational analysis 3. Interpret results of the methodology 4. Generate final erosion potential risk maps for Central Stroubles watershed in the Town of Blacksburg, VA 5. Create a procedure for municipal governments to produce EP risk maps 9

10 IMPORTANT PARAMETERS From Literature: Runoff Volume Slope Land Cover Soil Erodibility Rainfall Intensity 10

11 IMPORTANT PARAMETERS Site Component Runoff Volume (V R ) Local Slope (S L ) Land Cover (LC) Soil Erodibility (K f ) Transport Component Distance to nearest stormwater conveyance point (D) Slope along surface flow travel path to nearest stormwater conveyance point (S A ) Rainfall Intensity Excluded Homogenous across watershed Relative EP ranking 11

12 EROSION POTENTIAL Site Component Downstream Transport Component EP = Erosion potential V R = Accumulated runoff volume S L = Local slope of the cell LC = Land cover K f = Soil erodibility D = Distance to inlet S A = Average slope to inlet Minimum Score Maximum Score Site Component 1 10,000 Downstream Transport Component Erosion Potential 2 10,100 12

13 CENTRAL STROUBLES WATERSHED Case Study: Central Stroubles 10 x 10 meter raster analysis (smaller gave major runtime problems) Land Cover Types Residential Commercial Urban Old Blacksburg High School Data Used Westview 2-ft Contours lines to DEM Cemetery Stormwater Infrastructure points Detailed Land Cover Database (DLCD) Web Soil Survey (WSS) polygon National Hydrography Database (NHD) Flowlines Aerial Imagery 13

14 DEM VS WATERSHED DELINEATION Digital Elevation Model 2 ft contours Not infrastructure corrected Watershed Delineation Infrastructure corrected Issues with DEM crossing Watershed delineation when finding flow paths 14

15 DEM VS WATERSHED DELINEATION Digital Elevation Model 2 ft contours Not infrastructure corrected Watershed Delineation Infrastructure corrected Issues with DEM crossing Watershed delineation when finding flow paths 15

16 EVALUATING LAND SURFACE EROSION Stream Locations Excluded Streambank erosion not addressed by this procedure Based on non-weighted flow accumulation Threshold values established by NHD flowlines, aerial photo and channel cross sections 16

17 SITE COMPONENT: PARAMETERS Runoff Volume, V R Relative Rank Local Slope, S L Absolute Rank Rank 2 Yr. Runoff Volume (ft 3 ) , , , , ,757 Land Cover, 7 LC Soil 15,789 Erodibility, K f Absolute 8 Rank Absolute 22,859 Rank 9 33, ,898 17

18 SITE COMPONENT: PARAMETERS Runoff Volume, V R Relative Rank Local Slope, S L Absolute Rank Rank 2 Yr. Local Runoff Slope Volume (degrees) (ft 3 ) , , , , , Land Cover, 7 LC Absolute 8 Rank Soil 15, Erodibility, K f Absolute 22, Rank 9 33, ,898 >= 45 18

19 SITE COMPONENT: PARAMETERS Rank Land Cover 1 Impervious 2 ~ not assigned~ 3 Dense Forest 4 Light Forest/Tree Canopy 5 Brush/Bush 6 Open Space (Lawn) Runoff 7Volume, V R Local Gravel Slope, S L Relative 8 Rank Light Bush/Dirt/Mulch Absolute Rank 9 ~ not assigned~ 10 Dirt Land Cover, LC Absolute Rank Soil Erodibility, K f Absolute Rank 19

20 SITE COMPONENT: PARAMETERS Rank Soil Land Erodibility Cover 1 Impervious ~ not 0.14 assigned~ 3 Dense 0.21 Forest 4 Light Forest/Tree 0.28 Canopy 5 Brush/Bush Open Space 0.42 (Lawn) Runoff Volume, V R Local Gravel Slope, S L Relative Rank Light Bush/Dirt/Mulch Absolute Rank ~ not 0.63 assigned~ 10 Dirt 0.7 Land Cover, LC Absolute Rank Soil Erodibility, K f Absolute Rank 20

21 TRANSPORT COMPONENT: PARAMETERS Rank Distance to Inlet Distance to Nearest Inlet, D Relative Rank (feet) Average Slope, S A 10 Absolute Rank727 21

22 TRANSPORT COMPONENT: PARAMETERS Rank Average Slope (degrees) Distance 9 to Nearest 42 Inlet, D 10 Relative Rank >= 45 Average Slope, S A Absolute Rank 22

23 DEFINING NEAREST INLET Conveyance Point Layer Infrastructure nodes Stream network points 23

24 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis 24

25 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis Compare Near_Dist To Flow Length Flow Length > Near_Dist Set Near_Dist as Near_Dist Set Rim Elev as Rim Elev 25

26 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis Compare Near_Dist To Flow Length Flow Length > Near_Dist Set Near_Dist as Near_Dist Set Rim Elev as Rim Elev 26

27 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis Compare Near_Dist To Flow Length Flow Length > Near_Dist Flow Length < Near_Dist Set Near_Dist as Near_Dist Set Rim Elev as Rim Elev Set Near_Dist as Flow Length Set Rim Elev as Elevation -delevtooutlet 27

28 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis Compare Near_Dist To Flow Length Flow Length > Near_Dist Flow Length < Near_Dist Set Near_Dist as Near_Dist Set Rim Elev as Rim Elev Set Near_Dist as Flow Length Set Rim Elev as Elevation -delevtooutlet 28

29 PYTHON SCRIPT Source Cell Elevation From DEM Select Inlets where Rim < Cell Elevation Run Near Analysis Compare Near_Dist To Flow Length Flow Length > Near_Dist Flow Length < Near_Dist Set Near_Dist as Near_Dist Set Rim Elev as Rim Elev Set Near_Dist as Flow Length Set Rim Elev as Elevation -delevtooutlet Average Slope = Elevation Rim Elev / Near_Dist 29

30 EVALUATING FLOW PATH LENGTHS Near Distance (ft) Measured Distance (ft)

31 EVALUATING FLOW PATH LENGTHS Near Distance (ft) Measured Distance (ft)

32 EROSION POTENTIAL RISK MAP Site Component Transport Component 32

33 EROSION POTENTIAL RISK MAP Site Component Transport Component 33

34 EP FREQUENCY DISTRIBUTIONS Transport Component Site Component Frequency 15,000 10,000 5, Erosion Potential Frequency 6,000 5,000 4,000 3,000 2,000 1, Erosion Potential Frequency 6,000 5,000 4,000 3,000 2,000 1,000 0 Erosion Potential Erosion Potential Median Score Site Component 30 Transport Component 8 Erosion Potential 38 34

35 INFLUENCE OF TRANSPORT COMPONENT Areas of high imperviousness and low slope In 14% of the cells, transport was > 50% of the EP. Only 25% of the cells contribute <10% Median contribution is 18% 35

36 ADAPTATIONS to EP EQUATION A C D E F B G H Unbalanced influence between site [10,000] and transport [100] component Equal weighting within components for each parameter Is slope as or more important than the rest? How much influence does land cover have? Comparisons between neighboring watersheds Absolute rankings for ALL parameters 36

37 CONCLUSIONS 1. Investigate the important parameters of soil erosion 2. Develop a method for determining Erosion Potential (EP) through GIS and computational analysis 3. Interpret results of the methodology 4. Generate final erosion potential risk maps for Central Stroubles watershed in the Town of Blacksburg, VA GIS Python EP 5. Create a procedure for municipal governments to produce EP risk maps 37

38 CONCLUSIONS 1. Investigate the important parameters of soil erosion 2. Develop a method for determining Erosion Potential (EP) through GIS and computational analysis 3. Interpret results of the methodology 4. Generate final erosion potential risk maps for Central Stroubles watershed in the Town of Blacksburg, VA GIS Python EP 5. Create a procedure for municipal governments to produce EP risk maps 38

39 CONCLUSIONS 1. Investigate the important parameters of soil erosion 2. Develop a method for determining Erosion Potential (EP) through GIS and computational analysis 3. Interpret results of the methodology 4. Generate final erosion potential risk maps for Central Stroubles watershed in the Town of Blacksburg, VA GIS Python EP 5. Create a procedure for municipal governments to produce EP risk maps 39

40 FUTURE WORK Improvements to infrastructure corrected DEMs Incorporation of downstream land cover influence on transport erosion 40

41 QUESTIONS? Contact: 41