Water Quality Risk Assessment - Esri › library › userconf › ... · Stormwater System Plan...
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Stormwater System PlanWater Quality Risk Assessment
John Henry Burns, PE City of Portland Bureau of Environmental Services
Arnold Engelmann DHI Water and Environment, Inc.
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01.
Project Description
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Project Description
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• Goal: Develop a plan to guide investment in Portland’s stormwater
system over the next 30 years.
• Context: Portland just finished a $1.4B project to control sewer
overflows and manage stormwater in the central portions of the city.
The next phase of stormwater investments will focus on the surface
streams and stormwater infrastructure outside the combined sewer
area.
• Approach: An asset-based prioritization, focused on identifying risk
and then evaluating options to reduce risk. Rely on existing asset
inventories and available terrain and landuse data sets.
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Project Description
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Outcomes: Stormwater flow and volume estimates and annual pollutant
load estimates for all stormwater assets in the city inventory
• ~100,000 stormwater pipes and culverts
• ~10,000 mapped stream segments
• ~70,000 inlets / catchbasins
• ~20,000 stormwater treatment facilities
• 3’ grid cell digital elevation model, 600,000,000 cells
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Project Description
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Challenges:
• Incomplete asset inventory
• Spatial inaccuracies in inventory
• Corrections being made constantly
• Large data sources
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Strategic Commitments Stormwater Services
Stormwater is managed to meet regulations
in a watershed context to achieve:
Services delivered to the customer - What
we manage to reduce risk & improve
conditions:
protection of public health and property and
improvement of public safety
• sanitary sewage releases
• erosion and landslide hazards
• localized/nuisance flooding
• groundwater contamination
protection of biological communities and
improvement of ecological function
• loss of habitat
• contamination of surface water and
sediment
• disruption to hydrologic cycle
support of community needs• deficiencies that impede community
improvements
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Asset Management and Risk Assessment
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Spatial
Resolution / Scale
Citywide
Sub-
watershed /
basin
Project /
Site
Assess Risk
Develop
Solutions
Design and
Construct
Planning PhaseNumber of Assets
Evaluated
~100,000
~1,000
10
Confidence / Accuracy
of Evaluation
Low
High
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Asset Management and Risk Assessment
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𝑹𝒊𝒔𝒌 = 𝑪𝒐𝒏𝒔𝒆𝒒𝒖𝒆𝒏𝒄𝒆 𝒐𝒇 𝑭𝒂𝒊𝒍𝒖𝒓𝒆 ∗ 𝑳𝒊𝒌𝒆𝒍𝒊𝒉𝒐𝒐𝒅 𝒐𝒇 𝑭𝒂𝒊𝒍𝒖𝒓𝒆
• Risk of a pollutant washing in to a receiving water
− Likelihood: How much pollution washes off a given surface?
− Consequence: How susceptible is a receiving water to that pollutant?
− Assign scores to likelihood and consequence, and calculate the relative water quality risk.
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02.
Maps and Data Source
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Asset Inventory Base Layers
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Supplement the Base Inventory
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Estimating Volume and Flow Rate
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Landuse Classification
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03.
Process Details
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Overview
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• Framework
− Extract flow paths above and below ground
− Flow accumulation and “decumulation”
• Two worlds combined
− Raster: Above ground hydrology
− Vector: Below ground infrastructure
− Combined: Geometric network of stormwater flows
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Linking Surface and Subsurface
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• Trace surface flow along paths of steepest descent
• Linking of overland and underground flow: Inlets and Outlets
• Each inlet has a catchment area.
• Outlets flow into the catchment of another inlet or out of the system.
Catchment Catchment
Inlet
Outlet
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Zooming out a bit…
Flow Accumulation - Surface
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Just like we can walk upstream to identify catchments, we can walk downstream
to follow flow paths and identify channels
Flow Accumulation - Surface
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We can count the number of grid cells upstream of a particular cell
Thicker lines represent flow paths with more cells upstream
Flow Accumulation - Surface
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We aren’t really concerned with flow off every single 3’ grid cell, so trim out the
flow lines below a threshold
For the PoC, we trim out all flow lines less than 300’ long, which per the Sewer Design
Manual is the point at which runoff transitions from sheet flow to channel flow
Flow Accumulation - Surface
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Zooming out a bit more…
Note the gridded nature of the data starts to become obscured
as we zoom out
Flow Accumulation: Surface
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Linking Surface and Subsurface
We can combine that surface channel identification and tracing algorithms with a
pipe network tracing algorithm
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Filling of DEM
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Goal:
• Prevent filling of sinks which are “true” sinks.
• Allow filling for other anomalies.
• Stop flow paths at inlets.
Solution:
• Punch “holes” into the DEM.
• Set location of inlets to “No Data”.
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© DHI
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© DHI
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© DHI
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© DHI
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© DHI
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© DHI
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Water Quality Load Accumulation
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• Tracking of multiple pollutants using landuse loading values.
− TSS, TP, BOD, E Coli, PbD
• Accumulation of loads through system.
• Reduction of loads through Pollution Reduction Facilities.
− Concentration based
− Flow volume reduction
− No increase in loads
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Results
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• Volume and flow rate estimates
• Load and concentration estimates for every asset in the system
− Pipes, ditches, culverts, streams can all be queried to determine
water quality risk
− Sumps, swales, filters, can all be queried to determine total load
reduction
• Classification system defining susceptibility of an asset to a pollutant
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Total Risk Maps
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Implementation
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• Technologies:
− ArcGIS (ArcObjects/Geoprocessing)
− Custom Code (Eclipse Public License – Google Code)
− TauDEM (David Tarboton, Utah State University)
• Languages:
− C#, Python
• Automated Build:
− Windows Batch, Windows Scheduler
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Thank you
John Burns, PE: [email protected] Engelmann: [email protected]
© DHI
Source Code: https://code.google.com/p/besasm-swsp/TauDEM: http://hydrology.usu.edu/taudem/taudem5/index.html