A$$et Management With GISA Stormwater Utility Perspective

What does a Stormwater Utility do?

• Road drainage

Maintenance, repair & construction of stormwater pipes

• Dams Prevent downstream flooding

• Water QualityRegulatory compliance & reducing pollution

Then (pre-2006)

• Reactive utility

• Funding source – general tax fund

Historical Service Requests

Water

Federal EPA(Agency)

NPDES permit (1990)Large cities > 100K

Nonpoint Source PollutionImprove Watershed

Reduce Pollutant Loadings - TSS(Fecal Coliform, Biota – Fish & Macroinvertebrates)

Federal Clean Water Act of 1987 And Amendments

State EPD (Division of DNR)

County and Municipal Stormwater Plans

Now (2006 & Forward)

• Proactive Utility

• Technology

Decisions, Decisions

• Identify most vulnerable assets

Through critical analysis.Criteria were identified through brainstorming. What data supports the analysis?

Why waste time and resources inspecting good features?

Who gets involved?• WIP• DAMS• Construction plans• Maintenance

•Compliance (with WQ)•Inspections (SRs)•GIS

How Do We Decide? Then: “Respond to Service Requests” & “Do pond inspections”

Now: NPDES 5 year permit from EPD “Inspect 10% of the total assets” “Inspect 20% of the most critical over 5 years & repair if needed”

Maximum Cost Benefit

What is the most critical?

• Risk Assessment ModelLikelihood of Failure Consequence of Failure

Likelihoodof failure y-axis

Criteria Weight

Corrosive Soils 20

Age, % of useful remaining life 80

Pipe material 100

Inspection results 100Inspection results: Inventory based on Good/Fair/Poor Objective Visual Assessment Inventory done over several years beginning in 2000

Criteria Scoring ( 0 = low consequence, 10 = high consequence)* factor of ten

Consequenceof failure x-axis

Criteria WeightDiameter 90

Potential for Safety Risk and/or Property LossProximity to buildingsProximity to Critical Facilities (hospitals, fire stations, etc.)Proximity to roads and bridges

808080

Proximity to Impaired (303(d)) Streams 40

Proximity to Environmentally Sensitive Areas Watershed improvement projectsDrinking water sources

3030

Criteria Scoring ( 0 = low consequence, 10 = high consequence)* factor of ten

Y-axisInitial Development-Likelihood

X-axisInitial Development - Consequence

Y-axisFinal Likelihood Weights

X-axisFinal Consequence Weights

Data Clean-up & Building of Ranges

Soil type

All Gwinnett County soil is acidic

Codes of pipes

Data Dictionary or Metadata for Codes

Pipe life expectancy

Pipe Life Expectancy

Assuming You Have Stormwater Inventory Data…

2000 2002 2004 2006 2008 2010

Whole subdivisions

Last Contract Deliveries

GPS in-house

Digitized from plats/fieldwork

PondsContracted Out Inventory/Assessment

Assuming You Have Stormwater Inventory Data…

Select county maintained pipes

Start with Existing STW Attribute Table

Build “Likelihood”

Quantifiable data…

Create new fields

Then

Now

Diff

Material_l

field calculate them

Create New fields and Field Calculate

Create new fields

Remainlife

Perc_RUL

field calculate them

Create New Fields and Field Calculate

Create new fieldRUL_score

Select records

Perc_RUL <= 20

Field calculate RUL_score

10 * 80 (weight*factor) = 800

Complete the remaining records

by selected ranges

Finish Loading the RUL_score Data Fields With Final Scores Based on Weight

Create new fieldMaterial_S

Select records “PL” or “CO”

Field calculate Material_s10 * 100 (weight factor) = 1000

Complete the remaining records by selected ranges

Finish Loading the Material_s Data Fields with Final Scores Based on Weight

Build ConsequencesAll consequences are related to proximityExcept for Pipe Diameter

Use the “Join data from another layer based on spatial location”. “Minimum”.

Final Matrix

Graph the results in the *.mxd …

You can select the most critical likelihood and consequence scores in the graph and see them in the view

Graph the resulting matrix in the *.mxd Tools>Graphs>Create>Scatterplot

Unranked pipes pre-SAMP

Ranked Pipes with SAMP

Most Critical Pipes with Flood Sites

*.avi

800 of the most critical pipes

Results (static image)

Annual Pipe Inspections

Total pipe assets

20%

20%

20%

20%

20% annual inspection

Total pipe assets

10%

10%

10%

10%

10%

10%

10%

10%

10%

10%Critical pipes thoroughly pole camera or video inspected annually – PACPS.

Within 5 years, all the most critical will have been inspected.

Pre-Suggested by EPD Approved with SAMP

The critical pipes happened to be 5% of the total pipe mile assets.

EPD Approved!

This is the first known SAMP for SEPARATE (MS4) stormwater system in the USA

Critical Pipes With Contiguous Inspection

Critical Pipes with

Contiguous Inspection

Priority 1 Flood Sites

Priority 2 Flood Sites

Priority 3 Flood Sites

The Cycle of Review

What did inspections reveal?

Should we revise criteria for rating pipes?

Is the SAMP working?

Do we re-run the matrix with refreshed scores?

Are there other consequences

to consider?

Contactswww.gwinnettstormwater.com

678-376-7193

• Steve Hart, Planning ManagerSteve.Hart@gwinnettcounty.com678-376-6925

• Karen Lougee, GIS IIIKaren.Lougee@gwinnettcounty.com678-376-6719

• John Dean, GIS IIIJohn.Dean@gwinnettcounty.com678-376-6761