Gross and Effective Drainage Area Delineation in the Prairie Provinces

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Gross and Effective Drainage Area Delineation in
the Prairie Provinces

• Presentation at PPWB Prairie Hydrology Workshop
• January 29, 2013

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Overview

• Concepts
• Why is this of concern to the PPWB?
• Background
• Manual Process
• Migration to GIS Environment
• Recent Changes
• What Does the Future Hold?

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Concepts

• Stichling and Blackwell (1957) presented a paper
  proposing the concept of fluctuating drainage
  area by year, by season, by event
• Godwin and Martin (1975) presented a paper
  refining the concept of gross, effective and dead
  drainage areas

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Gross Drainage Area

• The gross drainage area of a stream at a
  specified location is that plane area, enclosed
  by its drainage divide, which might be expected
  to entirely contribute runoff to that specified
  location under extremely wet conditions. The
  gross drainage boundary is the drainage divide
  (i.e. the height of land between adjoining
  watersheds).

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Effective Drainage Area

• The effective drainage area is that portion of
  a drainage basin which might be expected to
  entirely contribute runoff to the main stream
  during a flood with a return period of two years.
  This area excludes marsh and slough areas and
  other natural storage areas which would prevent
  runoff from reaching the main stream in a year of
  average runoff.

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Dead Drainage Area

• Drainage is considered dead if there is no
  outflow from an area even under very wet
  conditions. This situation is common on the
  Canadian Prairies where major depressions having
  sloughs and shallow lakes with no outlets are
  usually associated with dead drainage. A dead
  drainage basin includes all of the area tributary
  to such a depression.

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Why is this of concern to the PPWB?

• Need drainage areas that are acceptable to all
  member agencies
• For purposes of apportionable flow determination,
  only projects within the effective drainage area
  are considered as depletions to the natural flow

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Background

• 1970 - PFRA, as part of an IHD Study, undertook
  task of delineating drainage areas (543 stations)
• Early 1970s - Need for standardization
• 1975 - at PPWBs request, PFRA accepted
  responsibility for delineating areas on streams
  covered by Master Agreement on Apportionment
  commitment reaffirmed in June 2003
• 1978 - Hydrology Memorandum 25 (1191 stations)
  and 3 subsequent addendums

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• 1983 - Hydrology Report 104 (1687 stations) with
  8 subsequent addendums (Addendum 8 published in
  2001 included 2689 stations)
• 1994 - Decision made to migrate data base and
  process to a GIS environment
• Late 1990s - digitizing lines and developing a
  GIS process
• 2001 - Completed migration from manual to GIS
  environment
• 2008 - Current GIS version (8) includes entire
  Prairie Provinces area (3312 stations)

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Manual Process

• Time consuming and resource intensive
• Difficult to update data base
• Limited product usability

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Index Cardsand Summary Reports
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Migration to GIS Environment

• Process
• - digitize delineated boundaries
• - develop gross effective polygons
• - develop linkage network
• - compare manual GIS tabulations to
  check/confirm linkages

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Migration to GIS Environment

• Benefits
• - data base easy to update/maintain
• - quick automated revision of areas
• - easy access of data base by users
• - unlimited application potential

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Recent Changes

• Association of all dead drainage areas with a
  drainage basin
• Addition of artificial stations to give
  complete coverage of Prairies

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Ongoing Enhancements

• Continue to refine delineations
• - use 120,000 scale coverage where available
• - check delineations using digital NTS maps
  (DEMs)
• Incorporate local information provided by users

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Current (Version 8, 2008) Product

• http//www.agr.gc.ca/nlwis-snite/index_e.cfm?s1da
  ta_donneess2detailss3lc-ctpagewb-bv_plus

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What Does the Future Hold?

• ?????? PFRA no longer exists, and there is no
  mandate in the current organization to continue
  drainage area delineation activities
• International Harmonization of Watershed
  Boundaries and Hydrographic Features (IJC)
• Development of Watershed Delineation Tool for
  specific projects, not for drainage area database
  maintenance

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Features of the Watershed Delineation
Toolhttp//www.agr.gc.ca/watersheddelineation

• Delineate watershed boundaries anywhere within
  the Canadian Prairies
• Produce maps and hydrology reports containing
  standard watershed information
• Delineated watershed boundary and area
• Contributing and non-contributing areas
• Longest flow path, stream length and slope,
  draiange density
• Location of WSC gauging stations
• Download watershed boundaries to standard
  geographic formats (KML or shape file)
• Easy to use and interactive

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• QUESTIONS???