stormwater geospatial tools - sediment pollution
TRANSCRIPT
Geospatial Tool DevelopmentGoal: To create geospatial tools to help support isolating significant sediment pollution sources.
Tool #1: Drainage Flow Tool #2: Land Use Land Cover (LULC) Raster / Mapping Bare Soils Tool #3: Soil Erosion Potential Hot Spot Analysis
Current Toolset Overview
Tool #1: Drainage Flow Tool What is it? A line layer that shows general stormwater flow across the terrain
LiDAR DEM Flow Accumulation
Once Flow Accumulation Minimum Basin Size is Met, Derive a Line
Feature
Our minimum Basin = 15 Acres
STREAMS+ DRAINAGE FLOW
Drainage Flow Tool continued
Pros:- Gives great insight
on stormwater movement across the terrain.
- Can be loaded into Google Earth to be compared with updated imagery.
Cons:- Currently
subsurface drainage in not incorporated (i.e. Pipes/Culverts).
Tool #2: Land Use Land Cover (LULC) Raster / Mapping Bare Soils What is it?
Raster dataset derived from semi-automated Image Classification method; classifies image colors into different groups called classes. The classes we used were Bare Soil, Forest, Grasslands, Urban, Water, and Shadows/Unknown.
Instead of being just an image color, it is now defined as what class that raster cell belongs to.
Derived from NAIP Imagery 1 Meter Resolution (good resolution for image classification, less computer resources needed) Georgia is flown every 1-3 years under the NAIP program; good long-term free source of
imagery.
Imagery
Classified Image
What’s Henry County Made Of?
(2013 Data)
Pros/Uses:- After we convert this
raster data to vector, we can measure amounts (i.e. Area or % of bare soil in sediment impaired stream basin, or by property parcel, etc.).
- Land Cover is an important part of hydro analysis; we’re successfully using this layer to size culverts.
- Urban is impervious surface, which our commercial stormwater fees are based on. We’ve used this layer to catch previous errors in our billing.
- Future Change Detection
Cons:- Like most automated methods, the dataset is not perfect and has some error (i.e. There is an unknown class, which is primarily shadows in the imagery. Dirty concrete has a very similar color to bare soil so there is some concrete incorrectly classified as bare soil).
Quick Comparison of Henry County LULC Raster to Publicly Available LULC Raster from NRCS
Henry County LULC Raster – 1 meter resolution
NRCS LULC Raster – 30 meter resolution
Tool #3: Soil Erosion Potential Hot Spot Analysis What is it?
Hot Spot Analysis highlighting areas that have 3 main ingredients for soil erosion: Flow Accumulation, Slope, and Bare Soils.
Length Slope Factor Formula = Power([flowacc] * resolution / 22.1, 0.4) * Power(Sin([slope] * 0.01745) / 0.09, 1.4) * 1.4
Flow Accumulation Slope Length Slope
Factor
Length Slope Factor
Bare Soils (from LULC)
High Potential for Soil Erosion
Hot Spot
Analysis
We’ve run this analysis in two different ways so far:Method 1: Running it on an entire basin.Method 2: Concentrating the hot spot analysis only within 50 ft of the drainage flow lines created previously, which could provide a direct pathway to our streams.
Took Length Slope Factor
from the RUSLE (Revised
Universal Soil Loss Equation)
Soil Erosion Hot Spot Analysis – Method #1: Entire BasinCase Study: Island Shoals Basin
Soil Erosion Hot Spot Analysis – Method #2: Within Drainage FlowCase Study: Island Shoals Basin
