Utilizing GIS for a Storm Drainage Utility Implementation

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Utilizing GIS for a Storm Drainage Utility
Implementation written and presented by Marikka
Williams, GISP, GIS Administrator, Highland
Village, Texas
autocad conversion
information integration
georeferencing
geostatistical analysis
database management
planimetrics
citizen follow up
storm drainage management
storm drainage delineation
storm drainage asset tracking
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Developing a Storm Drainage Fee Methodology

• Background Research
• - Legal Parameters
• - Precedents
• Investigating the Geography
• Performing an Exploratory Analysis
• Evaluating the Results
• Forming Strategies for Data Collection
• Forming Strategies for Filling in Data Gaps
• Implementing the Methodology
• Designing Follow Up Documentation
• Maintaining the System

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1987 Clean Water Act Amendment

• EPA developed the NPDES Stormwater Program
• Primary Objective is to Improve Water Quality
• Phase II regulations require Management Plan
• Gradual Implementation based on Population
• Development of Stormwater Drainage Utility

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Texas Statute 402.047b

• In setting the schedule of charges for drainage
  service, the governing body must base its
  calculations on an inventory of the lots and
  tracts within the service area. The governing
  body may use approved tax plats and assessment
  rolls for that purpose. The governing body may
  also consider the land use made of the benefited
  property. The governing body may consider the
  size, in area, the number of water meters, and
  topography of a parcel of benefited property, in
  assessing the drainage charge to the property.

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Determining the Best Avenue for Data Collection

• Appraisal District Records
• Pavement Inventory
• Aerial Photography
• Site Plans
• Permit Paperwork
• Estimation Techniques
• Field Verification

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Exploratory Analysis

• Landscape Evaluation
• Planimetric Data Collection
• Statistical Analysis
• Interpreting the Results
• Making Informed Decisions

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Pearsons Correlation Coefficient Statistic
Results
Driveways and Lots (.576)
Driveways and Garages (.155)
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Deciding on the Best Approach

• Proportional Data Collection
• Proportional Fee Distribution
• 1.20 Base Fee per 1000 sq ft
• Planimetric Data
• Algorithms

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Data Collection

• Appraisal District Records
• Geo-referenced Digital Site Plans
• Aerial Photography
• Permit Paperwork
• Estimation Equations

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Residential Data Collection

• Appraisal District Records
• Permit Paperwork
• Aerial Photography
• Estimation Equations

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Residential Appraisal District Records
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Residential Permit Paperwork
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Residential Planimetric Data Collection
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Residential Driveway Algorithm
Estimate 1 Calculates the percentage of the
driveway relative to the lot size.  The average
of all of the percentages in the category is the
value multiplied by the lot size to estimate
driveway area. Distributed into 6 broad
categories (Less than 10,000 sq ft 10,000-20,000
sq ft 20,000-30,000 sq ft 30,000-40,000 sq ft
40,000-50,000 sq ft Greater than 50,000 sq
ft)   Estimate 2 Proportional equation that
subtracts the footprint from the lot size and
calculates the percentage of the driveway
relative to the lot size minus the footprint. 
Average of all of the percentages in the category
is the value multiplied by the lot size minus the
footprint to estimate driveway area. Estimate 3
Equation that calculates the percentage of the
driveway relative to the lot size, where the
average of all of the percentages is multiplied
by the lot size, similar to estimate 1 but with
an increased number of categories. There are 54
categories in the 'Estimate 3' equation as
compared to the 6 categories in the 'Estimate 1'
equation.  The categories for Estimate 3 were
established in 500 sq ft increments.
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Residential Total Estimated Driveway Values

• Per a standard base rate of 1.20 per 1000 sq ft
  of impervious surface the total fees for the
  driveways that required estimation were
•  
• Estimate 1 (456.72)
• Estimate 2 (455.39) 
• Estimate 3 (460.53)
• Of the total fees collected these estimations,
  ranging from 2.28 to 13.76 for the driveway
  portion of the lot, collectively amount to about
  1 of the total drainage fee of 403,014
• The significant difference between the three
  estimates is in the manner in which the fees are
  distributed among the citizens
• Estimate 3 was selected as the best estimate for
  reflecting the closest approximation to reality
  and returning a greater amount of money for the
  budget that was most equitably distributed among
  the citizens
• Due to greater variability in the sample area
  paired with a decrease in sample size at the
  30,000 sq ft threshold the equation shifts to the
  Estimate 1 equation to smooth out this
  variability and increase sample size

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Residential Drainage Fee Assessment
The final set of equations utilized to calculate
the residential drainage fees are summarized as
follows EDS LS CP IS 1F G D DF IS
/ 1000 1.20 EDS Estimated Driveway Size LS
Lot Size CP Category Percentage 1F First
Floor Square Footage G Garage Square Footage D
Driveway Square Footage IS Impervious
Surface DF Drainage Fee
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Commercial Data Collection

• Planimetrics
• Aerial Photography
• Geo-referenced Digital Site Plans
• Appraisal District Records
• Permit Paperwork

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Commercial Data Collection Planimetrics
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Commercial Data Collection Permit Paperwork
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Commercial Data Collection Digital Site Plans
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Commercial Data Collection

• The equations utilized to calculate the
  commercial drainage fee distribution, where FP
  Footprint IFP Individual Footprint TFP
  Total Footprint PL Parking Lot PD Pavement
  Distribution IS Impervious Surface and DF
  Drainage Fee, are as follows
• 1. The first equation addresses the scenario
  where two or more commercial structures with
  individual domestic meters are located on one lot
  and share a parking area. This equation is
  calculated so that pavement is proportionally
  allocated to each business.
• (IFP /TFP PL) PD
• The total impervious surface equation for
  individual commercial structures that have been
  allocated a percentage of the pavement is
• PD FP IS
• 2. The second equation addresses the scenario
  where one commercial structure or a group of
  commercial structures share a lot and are
  assigned to one domestic meter. This equation
  simply adds the footprint to the pavement.
• PD FP IS

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Commercial Drainage Fee Assessment
The final set of equations utilized to calculate
the commercial drainage fees are summarized as
follows (IFP /TFP PL) PD PD FP IS DF
IS / 1000 1.20 PL Parking Lot TFP Total
Footprint IFP Individual Footprint FP
Footprint PD Pavement Distribution IS
Impervious Surface DF Drainage Fee
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Advantages of Utilizing a GIS

• Objective basis for measuring impervious surface
• Integrate and organize a large amount of data
• Perform exploratory analyses
• Follow up with tangible map products
• Leverage data to facilitate future storm drainage
  analyses

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Tangible Follow Up Documentation
Residential
Commercial
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Future Storm Water Management Applications
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Storm Water Drainage Utility Management

• Asset Management
• Hydrological Analysis
• Delineation of Drainage Network
• Model Drainage Behavior
• Identify Potential Hazards in advance of flood
  events
• Prediction and Prevention of Water Contamination
• Tracking and management of the testing of
  outfalls
• Runoff Analysis
• Watershed Assessment
• Wide range of GIS tools to support Storm Drainage
  Utility

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Recommendations

• Invest in a full set of planimetrics
• Invest in Digital Elevation Model
• Invest in Current Aerial Photography
• Invest in GPS Devices to Track your Assets
• Invest in GIS to actively integrate and analyze
  these data
• Invest in the time to research applicable GIS
  applications
• Educate non-GIS professionals about the value of
  GIS
• Utilize GIS to facilitate storm water management
• Utilize GIS to facilitate municipal operations

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Future Possibilities

• "The application of GIS is only limited by the
  imagination of those who use it. - Jack
  Dangermond
• Our thoughts and imagination are the only real
  limits to our possibilities. - Orison Swett
  Marden
• Limitations live only in our minds. But if we
  use our imaginations, our possibilities become
  limitless. - Jamie Paolinetti
• The world is moved along, not only by the mighty
  shoves of its heroes, but also by the aggregate
  of tiny pushes of each honest worker. - Helen
  Keller
• Act as if what you do makes a difference. It
  does. - William James