mapping riparian corridors using hydrologic landscape analysis
TRANSCRIPT
Mapping Riparian Corridors using Hydrologic Landscape AnalysisTOM ROBINSONDirector of Conservation, Science, and InnovationBay Area Open Space Council
Synopsis
• There is a need in land conservation for more effective and efficientmapping of riparian zones
• Hypothesis: We can do a better job of mapping riparian zones by using new tools and data
• New methods could result in greater protection of riparian zones and their benefits to humans
Alluvial Riparian Zones
Watershed context Cross section perspectiveUSDA
Smith et al. (2008)
Fish and aquatic species habitatFlood water storage
and groundwater rechargeWater quality
Riparian Ecosystems: Time & Space
TIME: LONG PERIODS OF BOREDOM……….SPACE: MEANDER CORRIDORS
Riparian Conservation
Policy Definition
USFS Forest Practice Rules
Fixed-width buffer based on stream type (fish-bearing?)
County Zoning Ordinances
Fixed-width buffer based on stream order
NRCS RiparianManagement Zones
Fixed-width buffer based on objectives (e.g., erosion control)
California Wetland and Riparian Area Protection Policy
Variable width delineation method indevelopment (SFEI)
Two primary modes:1. Policy ($): One size fits all,
but cheap2. Voluntary, incentive-based
($$$): Can be comprehensive but expensive
Agriculture
Forestry
Riparian Easements
• Voluntary incentive-based approach
• $ to exclude development
• Long term needs of the river
• Need a boundary(a polygon)
• Gradation for negotiation
From Ilhardt, Verry, and Palik, 2000
Need: High quality delineations for easement structure
Riparian Corridor – Restoring Functional Width
Current Practices: Easements and Ordinances
100 meters1997 storm?
“Riparian-ness”
Figures from NRCS Forest Management
Guidelines
Riparian functions decrease as you move away from the river
How to characterize the ecotone?
?Build on previous
techniques to map this
zone
What are the map-able indicators of this zone?
New Riparian Mapping MethodsMapping the Area Affected Over Long Time Scales by Moving Water
From Dilts et al. 2011
Elevation Above Channel (EAC)
From Smith et al. 2008The Nature Conservancy
Active River Area (ARA)
From Benda et al. 2011
Regional Curves ofHydraulic Geometry
• Equations that relate Bankfull depth and width to drainage area
• Available for most of U.S.
From Collins and Leventhal (2013)
Drainage Area (mi2)
Bank
full
Dept
h (ft
)
y = 1.0195x0.3667
R2 = 0.92607
Bankfull Depth
2x Bankfull= “Flood-prone area” (Rosgen, 1994)3x Bankfull= “Predicted fluvial landscape” (Benda et al., 2011)
Case Study: Mark West CreekEvaluating these methods on the ground
Study AreaMark West Creek, Sonoma County, CA
Confluence of Mark West Creek and Porter Creek
Mapping the Fluvial Landscape
2x Bankfull= “Flood-prone area” (Rosgen, 1994)3x Bankfull= “Predicted flucial landscape” (Benda et al., 2011)
Width at BankfullWidth at 2x Bankfull
3x Bankfull
Regional curve equation of Bankfull Depth versus Drainage Area (Collins and Leventhal, 2013)Dbf = 1.0195x0.3667
where x = drainage area
+1-meter LiDARdigital elevation model
Fluvial Landscape Model Overview• 3 raster inputs:
– Stream mask raster (Arc Hydro Tools and SetNull) – Flow Accumulation raster (Arc Hydro Tools)– Elevation (e.g., high-resolution DEM)
Bfl_elev = ((1.0195 * (([FLOW_ACC] * 9) / 27878400)^0.3667) * %Bankfull multiple%) + [ELEVATION]
User-definedvariable
(> 0)
Extract Multiple Values to Points
Streamraster
Streampoints
Flowaccumu-lation
Elevation
FLOW_ACC ELEVATION Bfl_elev
25041980 467.78 476.56
25038770 468.82 477.60
24991310 474.09 482.86
y = 1.0195x0.3667
Field Calculator
Use of Inverse Distance Weighted (IDW) for Extrapolation
• Need: Give Bankfull depth value to closest associated cells within the riparian corridor
• Creates the Bankfull elevation raster to use with elevation raster• Output: all cells at or below Bankfull elevation
Elevation Riparian zone (4X Bankfull Depth)IDW Extrapolation Output<= =
Model results
Fluvial LandscapeAssumption: we’re 100% confident this area is riparian
Elevation Above Channel
1 x Dbf2 x Dbf3 x Dbf
Evidence of flooding
Evidence of channel migration
Avulsion
1942 centerline in bluePresent centerline in yellow
Going Beyond the Fluvial Landscape with Indicators of Riparian FunctionSoil Moisture/Depth to Groundwater Upslope Contribution Areas WetlandsShading
Indicators of “riparian-ness”
Topographic Wetness Index:Depth to Groundwater & Soil Moisture
Indicators of riparian function
Upslope contribution – Flow accumulation (MD∞ method)
From Seibert & McGlynn 2007
D8 method(ArcGIS)
MD∞ method
Indicators of riparian function
Palustrine Wetlands
scouring-rush horsetail (Equisetum hyemale)
Indicators of riparian function
Shading and Organic Material Inputs
75 feet
Reality Check!Creation of a ground-truthed riparian zone map for comparison
Gravelcobble
Roots, cobbles in soil,
bedrock
Cobble, sand, willow, alder, cottonwood, bay
laurel
Grassland, wetland, valley oak, bay laurelgood soil development
Mixed oak woodlands, conifer forests
Scarp Channel Floodplain Terrace Upland Fringe
Landform mapbased on field surveys and DEMAlternative name: The map that would take too long to create for every potential riparian conservation easement project
Upland Fringe Upland Fringe
Acquisition ScenariosGiving practitioners data to make decisions
Delineating the Functional Riparian Zone
Upland Fringe Upland Fringe
Delineating the Functional Riparian Zone
Blue areas =Area under 18x Bankfull Depth
Acquisition Scenarios
Binned EAC into 4 scenarios (A = 5xBFD, B = 6x, C = 10x, and D = 18x)
Conservation Scenarios
Acquisition
Scenario
Additional
Shading
Canopy
(ha)
Additional
Wetlands
(ha)
Additional
High Soil
Moisture (%
of High TWI)
% of Functional
Riparian Zone
Covered
(cumulative)
Total
Land
Area
(ha)
Acquisition
Cost*
($)
A 6.1 0.32 31.0 26 11.1 $244,200
B 2.2 0.20 26.6 46 19.4 $426,800
C 3.4 0.03 31.7 77 32.4 $712,800
D 0.9 0 10.7 100 42.2 $932,800*Based on $22,000/ha estimate from Sonoma County Agricultural Preservation and Open Space District.
What’s it worth to you?
Marginal Gains
Where are the break points?
Different indicators but approximately the same
Benefit-to-Cost Ratio
Acquisition
Scenario
Relative
Increase of
Indicators of
Function (%)
Additional
Land Area
(ha)
Acquisition
Cost of
Additional
Area ($)
Benefit-to-
Cost Ratio
A 46 11.1 244,200 1.88
B 27 8.3 182,600 1.47
C 21 13.0 286,000 0.75
D 6 9.8 220,000 0.27
𝐵𝐵𝐵𝐵𝐵𝐵 = (𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝑜𝑜𝑜𝑜 𝐹𝐹𝐹𝐹𝐼𝐼𝐼𝐼𝐹𝐹𝐹𝐹𝑜𝑜𝐼𝐼𝐼𝐼 × 10,000) ÷ 𝐴𝐴𝐼𝐼𝐴𝐴𝐹𝐹𝐹𝐹𝐼𝐼𝐹𝐹𝐹𝐹𝐹𝐹𝑜𝑜𝐼𝐼 𝐵𝐵𝑜𝑜𝐼𝐼𝐹𝐹
More land doesn’t always mean more benefit…
Significant breakpoint
Scaling to the Catchment Watershed-scale conservation planning
Catchment-Scale Conservation Planning18xBFD
Evaluate for:• Level of protection• Impacts/development
A
B
Protected
Protected
Protected
Protected
Site EvaluationA
B
Conclusion New methods can mean more conservation
Implications: Riparian easement
Future Research
• More sensitive indicators (biological, groundwater). Example: Is there a correlation between the alluvial hotspots and fish/roe counts?
• Repeated study with multiple sites stratified by climate, watershed gradient
• Test performance using lower resolution terrain data (e.g., 5, 10, or 30-meter) and lower point density LiDAR (1-3 points/sq meter)
• Is there a threshold that characterizes riparian zones throughout a catchment? (creation of a credible watershed-wide alluvial riparian zone map)
Thank youTom Robinson | [email protected]
Collaborators:Dr. Jerry Davis, San Francisco State UniversityDr. Nancy Wilkinson, San Francisco State UniversityKaren Gaffney, Sonoma County Agricultural Preservation and Open Space DistrictDr. Ralph Dubayah, University of MarylandMark Tukman, Tukman Geospatial LLC
Funding provided by:Sonoma County Agricultural Preservation and Open Space DistrictRobert & Patricia Switzer FoundationCalifornia State University Council on Ocean Affairs, Science, and Technology (COAST) Program