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If the Leakage Type specified on the Geomembrane tab is Rowe et. al., 2004 one of the Rowe Leakage tabs will be displayed. The tab displayed will depend upon the Calculation Method selected.
Calculation Method: The method used to calculate the leakage can be either:
LEAK - a circular hole in a geomembrane in direct contact with the foundation (similar assumptions to Giroud but allowing one to consider more variables) or
Wrinkles - for a wrinkle (or series of wrinkles) with holes (the most realistic situation for many applications).
If the Calculation Method is selected as LEAK the tab will be displayed. The following parameters can be specified:
Hole Frequency: This is the number of holes in the geomembrane per hectare or acre. The default is 2.5 holes per hectare. See Rowe et al (2004, Chapter 13) for a discussion of the number of holes per hectare.
Hole Radius: This is the average radius of the holes in the geomembrane. The default is 0.00564 m.
Wrinkle Radius: This is the optional average radius of the wrinkles in the geomembrane. The default is 0.00564 m. A "circular hole" can be either a wrinkle or a hole (both involve fluid in direct contact with the underlying clay liner. The only differences are (a) the wrinkle is bigger and (b) if it is a wrinkle then you also need a hole in the wrinkle and leakage through that hole can be controlled by benoulli's equation).
CFLAG: This is either 1 or 0 depending upon the boundary. CFLAG is 1 when head in the underlying aquifer is greater than zero, and is 0 when the head is greater than the thickness of the soil layer above the first aquifer.
Transmissivity (THETA): A detailed discussion of this is given by Rowe (1998) and the effect of this parameter is examined by Rowe et al (2004). Values used in examples include: 1.6x10-8 m2/s for “good contact” between a geomembrane (GM) and compacted clay liner (CCL), 1.x10-7 m2/s for “poor contact” between a GM and CCL, and 1.x10-10 m2/s for “typical” contact between a GM and geosynthetic clay liner (GCL).
Conductivity (KOM): This is the hydraulic conductivity of the collection system or other material directly above the hole in the geomembrane. The default is 1x10-4 m/s.
If the Calculation Method is selected as Wrinkles the tab will be displayed. It is suggested that you sketch up the proposed idealized wrinkle configuraion to make sure that it makes physical sense. It is easies to work in term of hectares and remember that a hectare is 100mx100m square. When modelling Wrinkles one is modelling those wrinkles that have holes. The frequency gives the number of wrinkles with holes per heactare (or acre) while the spacing and length give the typical wrinkle dimenstions. For the default 10 (100m long) wrinkles/ha the spacing must by 10m (100m/no of wrinkles=10). For 5 (100m) long wrinkles the spacing would be 20m (100m/no of wrinkles=5). But if the wrinkles were only 20m long one could have 12 of them (three row of 4) with a spacing of 25m (100m/4 wrinkles per row).
The following parameters can be specified on this tab:
Wrinkle Frequency: This is the number of wrinkles per hectare or acre. The default is 10 per hectare.
Wrinkle Width: This is the average width of the wrinkles. The default is 0.3 m.
Wrinkle Spacing: This is the average spacing between the wrinkles. The default is 10 m.
Wrinkle Length: This is the average length of the wrinkles. The default is 100 m.
Wrinkle Hole Radius: This the average radius of the holes in the wrinkles. The default is 0.00564 m. This will limit the leakage that can occur through a given wrinkle.
Transmissivity (THETA): This is the same as that used in the LEAK method and is described on the previous page.
Conductivity (KOM): This is the same as that used in the LEAK method and is described on the previous page.
Calculate Leakage: This button can be used to calculate and display the leakage (Darcy velocity) through the geomembrane.