JoCo Stream Asset Inventory

JoCo Stream Asset Inventory http://aims.jocogov.org

JoCo Stream Asset Inventory Goals • Inventory stream & critical natural resources in unincorporated Johnson County • Develop stream buffers Products • Stream Buffer Map & Stream Setback Ordinance • Stream Inventory Field Manual - 4 Methodologies http://aims.jocogov.org

Stream Buffering & Setbacks Project funded by Johnson County Public Works Stormwater Management and a grant from EPA http://aims.jocogov.org

Project Area http://aims.jocogov.org

Role of GIS • Develop GIS Model for rapidly calculating and assessing stream condition. • Use GIS for systematically determining ideal field sample locations. • Other miscellaneous tasks like owner notification, field data collection, etc. http://aims.jocogov.org

Project Approach Stream lnventory Recommendations Analysis GIS Analysis http://aims.jocogov.org

Stream Asset - GIS Model • Goals – • Use a variety of spatial datasets to test feasibility and accuracy of modeling stream types and condition • Support the field data collection efforts by validating field results http://aims.jocogov.org

Stream Type Characteristics • Type 1 - Highest Quality • Generally described as the highest quality naturally occurring stream with little negative impact. Erosion and sedimentation is low, water quality indicators are positive and the surrounding riparian zone is a healthy, mature, succession woodland or other high-quality environment. • Type 2 - High Quality • This type of stream may have some down or side-cutting however, bank and bed composition (bedrock) assist in keeping the impact low. Water quality is generally good and the riparian zone is largely intact, although vegetation may be altered from that of a typical native plant association. • Type 3 - Restorable • Deterioration of the riparian corridor is more noticeable. While some remnant plant associations may be present, overall vegetative canopy cover is comprised of immature tree species. The potential for restoration exists although erosion and sedimentation can be greater than desirable. • Type 4 - Low Quality • Impacts are greater on this stream type with significant indicators of bank erosion and sedimentation present. The adjoining riparian corridor may be intact but vegetation is not representative of a native plant association. • Type 5 - Lowest Quality • The channel in this type is the most changed. The riparian corridor is becoming impaired to the point of providing little protection or benefit, and erosion and sedimentation indicators are significant. Water quality is questionable with noticeable phosphate and nitrate loading (large algae blooms). http://aims.jocogov.org

Process • Generate streams and sub-watershed management units • Generate ideal field sample locations • Generate “curve” data • Intersect and aggregate data by management unit • Summarize data by intersection results http://aims.jocogov.org

Process • Solid Surface Data – DEM, DTM, contours, etc • Basis of all the surface analysis like flow, accumulation, watersheds, streams, etc… • ArcInfo Workstation – TopoGRID • Generate corrected DEM from elevation and water features • ArcView 3.x – Spatial & Hydro Analyst • Build & Process stream and watershed data • Extension to calc line slope, generate stream orders http://aims.jocogov.org

Process • Extract and clip elevation data to watershed • Script entire hydro model process in AML & Avenue • Calculate stream slope & stream orders • Slope – Average – Start to Finish • Sinousity – Curve/Line • Sample locations determined by midpoint of most downstream segment of each continuous stream order http://aims.jocogov.org

Streams Flow Accumulation Sub-Watersheds DEM Sample Locations Elevation Data Flow Direction http://aims.jocogov.org

Impervious Surface and Curve Numbers • Impervious surfaces are impenetrable by rainfall (i.e. roads, buildings). • The more impervious the surrounding ground cover is, the worse the water quality impact – it increases peak discharges and runoff. • Curve numbers used to define impervious surface. • Curve numbers are assigned based on a combination of soil type and land use – we used the appraiser’s ag coverage and property_pl datasets for land use. The higher the curve number, the more impervious the ground cover – they range from 0 to 98. • Curve number combinations are defined from NRCS TR-55 publication. • Building and edge feature classes from planimetrics were assigned a curve number of “98”. http://aims.jocogov.org

Process • Data • Property data with landuse, agricultural use • Soils • Tools • ArcGIS 9.0 – Modelbuilder http://aims.jocogov.org

Process • Join soils with both land use and agriculture datasets • Join curve number table based on both attributes • Merge datasets together with the agriculture feature class taking first priority. • Merge building and edge of pavement feature classes together and assign the highest curve number value to them • Overlay building and edge dataset over landuse-generated dataset. • Clip new feature class to each specific watershed http://aims.jocogov.org

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ModelBuilder Tips & Tricks • Clip out study area – overlay geoprocessing done entirely in memory which constrains large datasets. Large Overlay toolset available to download from ESRI. • It is not possible to calculate fields on a joined table – bug that will be fixed • Separate out one huge model into many small models. The strength is in planning the workflow. • Use scripting if you need conditional statements – can’t import a script into a model. It seems easier to run entire process through scripting not ModelBuilder. http://aims.jocogov.org

Process • ArcView script to apply the rules of the model. • Average curve weighted by area per management unit, total veg cover, and stream slope/sinousity. • Apply weighting or index to each indicator and sum to give total for relative condition. http://aims.jocogov.org

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Results GIS vs Field Results Aerial w/ GIS Result Aerial w GIS and Field Results http://aims.jocogov.org

JoCo Stream Asset Inventory