SNOW-WATER EQUIVALENT - Grasslsummerfallow at 0, cross-section A-A
mm
40
I I I I I I I I I I I I I I I
Distance (m)
Figure 9. Comparison of snow accumulation on grassland versus summer fallow.
catchments with fallow land but also with cropped land. It is likely this change that is responsible for the wetter regime associated with wetlands in cropped or fallow catchments.
3.22 Modelling wetland water levels
The analysis of the wetland water level changes and their physical causes is valuable insofar as it increases knowledge of the hydrology of wetlands. Obviously, with the knowledge that land-use changes can affect wetland water levels, the next step is to predict what those changes might be for given change scenarios. It is reasonable to expect land use to change from time to time. In addition, it is important to know what changes could be expected in wetland water levels given the expected changes resulting from increases in climate variability. To explore these issues, modelling is required.
The model chosen was SLURP, developed at the National Water Research Institute, (NHRI, and now NWRI). The SLURP model (Kite, 1996) requires the dividing of a watershed into Aggregated Simulation Areas (ASAs). Each ASA is then subdivided into areas of different land covers. For each land cover area, the model carries out a vertical water balance at a daily time step.
Four tanks, the canopy tank, the snow tank, the fast tank, and the slow tank, are used in each ASA to represent the capacities of canopy interception, snowpack, surface and upper topsoil storage, and subsurface storage, respectively. The precipitation is either added to the snowpack tank or the fast tank according to the critical temperature (usually OOC). The
snowmelt from the snowpack tank goes to the fast tank and then it infiltrates from the fast tank into the slow tank according to the Philip (1954) expression for flow in porous media.
When the depth of water in the fast tank is greater than the depression storage, surface runoff will be generated at a rate based on Manning’s equation. The slow storage contributes to subsurface runoff at a rate depending on how full the tank is and on the slow tank water transfer coefficient.
The evaporation is calculated for each land cover area in each ASA and is satisfied, if possible, first from the canopy tank, then the snowpack tank (if it is not empty), then from the fast tank and finally from the slow tank. The Granger method (Granger & Gray, 1989) for calculating evapotranspiration was used in this study.
The model has several parameters that required calibration. These include the infiltration coefficient of the fast tank under unfrozen and frozen conditions, the slow tank water transfer coefficient, the depression storage, and the maximum storage of the slow tank.
Before 1983, the drainage area was divided into two ASAs, one for the upland (cropland) and the other for the wetland. After 1983, the upland ASA was separated into two ASAs, one for each of cropland and grassland. Therefore, two sets of parameters for the upland area, one for cropland and the other for grassland, required calibration.
The parameter calibration for cropland was performed using data from the period 1969 to 1973. For grassland, the data from 1987 to 1990 was used. The reasons for choosing these calibration periods were:
l the dry-wet climatic conditions during these two periods allowed a range of hydrologic responses to be simulated. Some of the chosen years (1969, 1970, 1971, and 1973) received above-average precipitation, whereas 1972, 1987, 1988, 1989, and 1990 were relatively dry;
l the effect of land-use change on the water levels are not obvious within the first 3-4 years after conversion from cultivation to permanent grass cover (van der Kamp, et al., 1998), so it is assumed that there is no difference between cultivation and grass cover until 1987.
The calibration was performed by setting individual parameter values, making a series of simulations, generating water levels and then comparing the computed water levels with observed water levels until no change in an objective function (Blackie and Eeles, 1985) overestimated and the water levels in 1979, 1980, and 1996 are underestimated.
In general, the simulated water levels compared favourably with the observed water levels outside the calibration periods. The model represents the important hydrologic processes involved in the wetland water balance fairly well. Simulation results can and do snowfall to be uniformly distributed throughout the contributing watershed. The redistribution of snow into the wetland due to wind is not considered in the model.
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Secondly, meteorological conditions at the Saskatoon Airport, the location where climatic data was recorded, likely differed on many occasions from those occurring at the site, particularly for summer precipitation events that occurred during convective storms, because these tend to be localized.
The reason for evaporation underestimation could be attributed to the inadequate windspeed function in SLURP. This function was held as a constant instead of including wind speed and aerodynamic roughness for the particular land cover as variables.
The SLURP model with the same values for the parameters was applied to two other
3.3 The hydrology of reclaimed watersheds
The major focus of this research is into the efficacy of soil covers for the saline-sodic shale overburden. More specifically, research is in progress into the efficacy of various configurations of cover composed of glacial till and peat surface material in minimising the percolation of fresh water into the saline-sodic formation. This study includes three sloped plots of 1 ha each. Each plot has a different cover design. The research program includes the characteristics of the covers to be tested, the instrumentation program, and the modelling that will be done.
In addition, near the plots is a large area, including several wetlands and subsidence features, which have had a cover in place for 3-5 years. This area is also to be studied, in particular the characteristics of the wetlands. Some preliminary data have been taken at several wetland sites in this area. These data will provide some insight into the nature of the material and the hydrologic regime and water balance associated with the cover in those areas.
Some data on the saline-sodic material have been taken prior to laying of the soil covers in February 1999. In the summer of 1998, during a field trip, a flood intiltrometer was used to determine the infiltration capacity of this material on a grid 10m O.C. In addition, the soil profile at these locations was also determined.
Data acquisition at this site has just been put in place. The installed instrumentation is intended for monitoring of climatological, soil moisture, and runoff conditions. The climatological instrumentation includes a full climate station, including a Bowen’s ratio apparatus for determining evaporation. Soil conditions are monitored with an FDR (frequency domain response) unit and a neutron probe for measuring soil moisture, and soil suction is determined with thermal conductivity sensors - both commercial and some manufactured at the University of Saskatchewan. Runoff measurements will be made at the bottom of the slope for each of the plots. There have been indications of significant interflow so measurement devices to differentiate between overland flow and interflow will also be installed.
The infiltrometer tests on the saline-sodic substrate were relatively consistent. The predominant response was that the fresh water used for the tests caused the material to swell and to cut off further percolation within less than an hour of the beginning of the test. This indicates that downward percolation may be minimal if the swelling is complete. Some of the
1.6
-0.8
Pond bottom
-Calculated water level
Y1 -Auto. measured data
I ~
+ Measured water level -1.2 169 71 73 75 77 79 81 a3 a5 a7 a9 91 93 95
Simulation Year
Figure 10. Comparison of measured and simulated wetland water levels.
tests, however, showed continuing infiltration after some time, indicating that some of the cracks and macropores in the substrate remained open and transmitted water downward, sometimes at a very rapid rate. It remains to be seen how these cracks and macropores will affect the overall water balance of these test plots now that the soil cover is in.
Figure 11 shows some preliminary results from the measurement program. It shows that two deep holes were drilled; one upslope and one near the wetland. The former had no free water in it while the latter showed a water table 2 m down. Equally interesting is the electrical conductivity (ec) measured at various levels in the soil at the three sites indicated.
In the midslope and upslope locations, the ec levels are low at the surface, increasing downward in the profile and reaching a maximum in the overburden material. At the bottom of the slope near the wetland, the ec values are maximum near the surface and lower down below.
The reasons for these ec distributions are as follows. At the upslope locations, leaching is taking place, moving the salts from the surface material further down into the profile. At the downslope location, lateral movement of water from the wetland to an evapotranspiration zone just upslope from the slough is causing salts to accumulate near the surface there, as discussed in Stolte et al., 1992. Future data will yield much more information on the hydrologic system operative in different parts of the terrain.
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3.4 Post environmental impact assessment - Rafferty-Alameda project
The follow-up analysis of the Rafferty-Alameda project and its EIA some 6 years after the fact produced some interesting results (Stolte & Sadar, 1998). First of all, the most important factor in the performance of the project was that the drought that existed at the time
Figure 11. Profile upslope from wetland, including soil type and soil chemistry data.
of project construction lifted soon after completion of the project, and the years since have been relatively wet. This has resulted in a much more rapid filling of the reservoir than was envisioned at the time of construction and EIA of the project.
The rapid filling of the reservoir let to benefits flowing Corn the project much sooner than originally expected. For several of the wet years, the project provided some flood control benefits. The fisheries of both reservoirs have developed very rapidly. Recreational use of both reservoirs is quite intensive. Instream water quality downstream of the structures is better than was anticipated at the time of the EIA.
On the other hand, of course, the rapid filling of the reservoir led to the inundation of wildlife habitat much sooner than expected. However, since there was no habitat within the inundated area that was critical to endangered or rare species, the rapid inundation did not have a great impact in this regard.
An issue that deserves to be addressed in the future is the value of EIA processes that, based on the best information available at that time, lead to conclusions and actions that ultimately prove wasteful. An example in the case of the Rafferty Alameda project is the remediation effort that was put into fisheries during project construction. Little of that remediation work was really necessary given the rapid tilling of the reservoirs and the excellent fish habitat that they provide.
4 SUMMARY AND CONCLUSIONS
The author’s research program has developed from a strong focus on soil salinization to presently being mainly concerned with wetland hydrology and its application to soil cover design. The research into wetland hydrology deals with both the analysis of recorded water levels and their relationship to hydrologic factors and also with the modelling of these water levels with a view to determining how they will respond to changes in climate and land use.
FEARO, 1991.The Rafferty-Alameda Project: report of the environmental assessment panel, Federal Environmental Assessment Review Office, Ottawa, Ontario, 67 pp.
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George, R.J., 1991. Interactions between perched and deeper groundwater systems in relation to secondary dryland salinity in The Wheatbelt of Western Australia: Processes and Management Options. Ph.D. thesis, Univ. of Western Australia, Nedlands, W. A. 312 PP.
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Geoslope, 1999. SEEP/W and CTRAN\W Manuals, GEOSLOPE International, Calgary, Alberta, Canada.
Granger, R. J. and D.M. Gray, 1989. Evaporation from natural nonsaturated surfaces. Journal of Hydrology, 111, pp. 21-29.
Greenwood, E.A.N, Klein, L., Beresford, J.D. and G.D. Watson, 1985. Differences in annual evaporation between grazed pasture and Eucalyptus species in plantations on a saline farm catchment. Journal of Hydrology, 78:261-278.
Henry, J.L., Bullock, P.R., Hogg, T.J. and L.D. Luba, 1985. Groundwater Discharge from Glacial and Bedrock Aquifers as a Soil Salinization Factor in Saskatchewan. Can. J Soil Sci. 65: 749-768.
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Kite, G. W., 1996. Manual for the SLURP hydrological model, V. 10. National Hydrology Research Institute, Saskatoon, SK, Canada.
Lewis, M. F., 1993. Structural control of groundwater in agricultural areas of Western Australia. Memoirs XXIV Congress IAH, Oslo, ~~588-597.
Philip, J. R., 1954. An infiltration equation with physical significance. Soil Sci., 77(l), 153- 157.
Murkin, H.R., 1998, Freshwater Functions and Values of Prairie Wetlands. Great Plains Research. 8:3-15.
Peck, A.J., 1978. Salinization of non-irrigated soils: a review. Aust. J. Soil Res., 16:157-168.
Poiani, K. A., Johnson, W. C., Swanson, G. A. and T.C. Winter, 1996. Climate change and northern prairie wetlands: Simulations of long-term dynamics. Limnol. Oceanogr., 41, 871-881.
Sharma, M.L., 1984. Evapotranspiration From a Eucalyptus Community. Agric. Water Management. 8:41-56.
Sommerfeldt, T.G. and C. Chang, 1980. Water and Salt Movement in a Saline-Sodic Soil in Southern Alberta. Can. J. Soil Sci. 60: 53-60.
Stein, R. and F.W. Schwartz, 1990. On the Origin of Saline Soils at Blackspring Ridge, Alberta, Canada Journal of Hydrology, 117:99-l 3 1.
Stolte, W.J., 1993. The hydrology and impacts of the Rafferty-Alameda project. Canadian Water Resources Journal. 18(3)229-245.
Stolte, W.J., Barbour, S.L. and R.G. Eilers, 1992. A Study of the Mechanisms Influencing Salinity Development Around Prairie Sloughs. Trans. ASAE. 35:795-800.
Stolte, W.J., McFarlane, D.J. and R.J. George, 1997. Flow systems, tree plantations, and salinization in a West Australian catchment. Aust. J. SoiZ Res. 35: 1213-1229.
Stolte, W.J., George, R.J. and D. J. McFarlane, 1999. Modelling Subsurface flow conditions in a salinized catchment in south western Australia, with a view to improving management practices. Journal of Hydrology, Proc., 13(17) :2689-2704.
Stolte, W.J. and M.H. Sadar, 1993. The Rafferty-Alameda project: monitoring and mitigation after the environmental impact assessment. Can. Water Resources Journal. 23(2):
109-l 19.
Stolte, W.J. and M.H. Sadar, 1998. The Rafferty-Alameda project and its environmental review: structures, objectives and history. Can. Water Resources Journal. 18( 1)l - 13.
van der Kamp, G., Stolte, W. J., and R.G. Clark, 1998. Drying out of small prairie wetlands after conversion of their catchments from cultivation to permanent brome grass.
Journal of Hydrological Science, 44(3): 387-397.
Willems, D. W., 1995. Salinization mechanisms around prairie sloughs. MSc. Thesis, University of Saskatchewan, Saskatoon, Saskatchewan.
Woo, M. K., 1992. Impacts of climate variability and change on Canadian wetlands.
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Woo, M-K., and R.D. Rowsell, 1993. Hydrology of a Prairie Slough. Journal OfHydrology, 146: 175-207.