GIS for Drainage AssessmentAndrew Harrison, GISP Business Development ManagerThe Schneider Corporation(317) 826-7393 aharrison@schneidercorp.com

Overview

• Generating watershed from GIS data

• Use of calculation software to assess drainage districts with Parcel, Watershed & Soils Layers

Accuracy…

• Fancy software does not equal accurate data

• Additional data layers will only be as accurate as basemap

• Parcels must be maintained and up-to-date through a known date– almost all GIS layers will refer back to

ownership information (in local government)

Watersheds of the Past?

Software

• ESRI– ArcGIS/ArcInfo– Spatial Analyst– Hydrology Modeling Extension

Contours – 2’ Seamless

Linear Stream Features

Elevation Raster

Flow Direction Raster

Flow Accumulation Raster

Raster Streams Layer

Watershed Rasters

Assumptions and Obstacles:

• 3 things to know about drainage (assumptions)– Water runs downhill

• Water drains into streams

– Payday is Friday– The boss is a jerk!

• Obstacles– “Sinks” and “Peaks”– Culverts

“Fill” Process for Sinks and Peaks

Streams at Culverts

Zoomed Stream Elevation Raster

“Burning” in the Streams

Watershed Generation Process

• Hydrology Modeling extension is used to “burn in streams” and build watersheds using raster images created from contour data

• Computer generated watersheds are merged/attributed to match County’s existing tiered administrative watershed system

Threshold = 500 Watersheds

Threshold = 5000 Watersheds

Remember these?

Tiered Watersheds

Watersheds

Tiered Watersheds

SubWatersheds

Tiered Watersheds

Subsof Sub

Watersheds

Tiered Watersheds

Subsof Subs

of SubWatersheds

Tiered Watersheds

Subsof Subsof Subsof Subs

Watersheds

What can I do with this watershed data?

• Provide greater accuracy to what was originally a poor data source– Hand drawn maps– On-screen digitized

• More equitable assessment for drainage– Geogear draincalc

Draincalc Overview

• A tool to utilize watershed data

• Allows drainage officials to quickly, accurately create the assessment

• Utilizes the geoprocessing functionality of ArcGIS– Meant to allow non-GIS people to benefit from

GIS

Tiered Watershed Layer

Watershed/Parcel Overlay

Watershed/Parcel Intersect - Lower

Watershed/Parcel Intersect - Upper

Watershed/Parcel/Soil Intersect

Range of Watershed Assessment Options

• Flat rate per benefited acre

• Percent of total (benefited acres)

• Setting minimum assessment amount(s)

• Additional assessment options– Soils– Parcel class/landuse– Distance from hydrological features– Any customization you come up with

Individual Watershed Projects

Defined Watershed Project

Proportion of total - values

Create Assessment Methods

Apply Assessment Rule Selections

Reports

Hearing Notice

Print Assessment Schedule

Summary

• How is this useful in the local government office?– Using GIS we were able to work from only

contours and parcels– Generate watersheds– Calculate assessments for those watersheds– Print hearing notices– Mail merge to labels (by watershed)

Customizable Assessment Methodology

Customizable Assessment Methodology

Benefits

• What benefits are gained from using GIS for these tasks?– More accurate watersheds– More equitable assessment– Speed and efficiency

Thank you!

Presenter: Andrew Harrison, GISP Business Development ManagerThe Schneider Corporation(317) 826-7393 aharrison@schneidercorp.com