Pierre River Mine Project

WATER AENV SIRS 15 – 43
Section 12.1
• Then, AET is determined using the HSPF model. The input to the HSPF
model is PET and actual lake evaporation. In the HSPF model, AET for
specific sub-basin or land segment is calculated from five sources
(interception, upper zone, lower zone, baseflow and groundwater storages) as
a function of moisture storages and the PET.
Request 22b Clarify why the Morton method was used for HSPF modeling in deference to the
Thornthwaite or Penman-Monteith methods for ecosystems, or the Priestly-
Taylor method. Provide a summary of information that compares the selected
approach to these others, given that it could be argued that, for an extensive
landscape covering a large area with different soil moisture storage properties,
different advective wind and different precipitation patterns, Morton might not
provide as accurate a representation of AET as other approaches.
Response 22b The Morton’s method was used following a similar procedure to Alberta
Environment’s to calculate evaporation and potential evapotranspiration for the
Province of Alberta (AENV 1999).
References
There are several more or less empirical methods developed over the last 50
years by numerous scientists and specialists worldwide to estimate PET from
different climatic variables. These methods can be grouped into five categories:
1. water budget (e.g. Guitjens 1982)
2. mass-transfer (e.g. Harbeck 1962)
3. combination (e.g. Penman 1948; Morton 1983)
4. radiation (e.g. Priestley and Taylor 1972)
5. temperature-based (e.g. Thornthwaite 1948; Blaney-Criddle 1950)
The general conclusion from several studies in the literature that compare the
performance of the various methods (e.g., Biftu and Gan 2000; Xu and Singh
2002; and Weiß and Menzel 2008) using locally determined parameter values
was that all methods provide estimates of PET that are comparable to PET
estimated using the Penman-Monteith method.
The Morton’s method for estimating PET is practically similar to the Penman-
Monteith method. Morton’s method is based on solving simultaneously energy
transfer and balance equations, using a constant energy transfer coefficient,
unlike the Penman-Monteith potential evapotranspiration formulation in which
the energy transfer coefficient is a function of wind speed.
Abraham, C. (1999): Evaporation and evapotranspiration in Alberta: report 1912-
1985 data 1912-1996; Alberta Environmental Protection, Water
Management Division.
Biftu, G.F., and Gan, T.W. 2000. Assessment of evapotranspiration models
applied to a watershed in the Canadian Prairies with mixed land uses.
Hydrological Processes, 14: 1305–1325.
12-24 Shell Canada Limited April 2010
CR029