Water Stewardship

Ground Water Resources of British Columbia

Chapter 10 — Ground Water Resources of the Plateaus and Highlands Ground Water Regions

10.3 ALBERTA PLATEAU

by

K. Ronneseth

PHYSIOGRAPHIC SETTING

Holland (1964) quotes that the Interior Plains in northeastern British Columbia are represented by the Alberta Plateau and its subdivision, the Nelson Lowland (Figures 8.2 and 8.7). Both comprise approximately 10% of the land area of British Columbia. Lying east of the Rocky Mountains, the region is underlain by sedimentary rocks which are flat lying and gently dipping. The Alberta Plateau, to be discussed in this section, are upland areas generally standing between 3,000 - 4,000 feet and are flat or gently rolling.

Figure 8.2 Ground water regions

Figure 8.7 Ground water regions of the Plateaus and Highlands

The region is drained and incised by the Liard and Peace Rivers and their tributaries. Peak discharge occurs at the time of maximum snow and/or glacial melt and is complimented by precipitation which reaches its maximum in the summer months. The drainage is often poorly organized in the upland areas where large areas of muskeg exist. Refer to Figure 8.7 for the names and locations of major rivers found in the study area.

The majority of the Plateau is heavily wooded except along the Peace River (below 760 m elevation) which is only lightly wooded and under cultivation.

BEDROCK GEOLOGY

The Alberta Plateau is the product of numerous cycles of broad subsidence, marine and freshwater sedimentation, emergence and erosion cycles. The geology includes a succession of strata that range from Cambrian to Upper Cretaceous in age. It is the Cretaceous rocks of the Mesozoic Era that outcrop in Plateau Region. The rock types of importance from a hydrogeological standpoint, are the Dunvegan Formation (sandstones, shales and siltstones; minor conglomerates; few thin coals; largely non-marine; over 365 m thick) of Upper Cretaceous age and the Fort St. John Group (predominantly shales of marine origin; mudstones, sandstones, conglomerates and minor siltstones; 1500 - 1800 m in thickness) of Lower Cretaceous age.

For further information on bedrock geology, refer to Kindle (1950); Irish (1958) and (1961); Muller (1961); Thompson (1977); and Stott (1968) and (1982).

SURFICIAL GEOLOGY

The initial pattern of topography was developed during the Tertiary Period by mass wastage and fluvial action. Post orogenic and recent uplifts accelerated these processes (Hughes, 1967). The regime and wasting of glacial ice during the Pleistocene further modified these landforms and are responsible for the majority of the unconsolidated deposit found within the study area today. It was this Quaternary activity which has played an important role in controlling movement, storage and availability of ground water (Mathews, 1978).

In the latter part of the Quaternary, the study area has experienced at least three major advances of Continental and Cordilleran ice. It was the Continental (or Laurentide) ice sheets which dominated the Plains region during the Pleistocene. The greatest extent of Cordilleran ice occurred about 15,000 years ago when it overrode the foothills, then extending eastward it probably abutted the Continental ice sheet occupying the plains regions. Much of the Plains region experienced cyclical deposition sequences of fluvial gravels during non-glacial periods; lacustrine sands, silts and clays resulting from aggradation and ponding of the Peace River by advancing Continental ice; till deposition by the ice itself; and then sands, silts and clays deposited in a series of ice damned lakes (named Lake Peace) during the retreating stages of Continental glaciation (Mathews, 1978).

As the eastern front of the Cordilleran ice retreated from the Plains, back to the Foothills and the Rocky Mountains, it was responsible for the deposition of tills, glacial fluvial sands and gravels and glaciolacustrine sediments in numerous localities throughout the Plains/Foothills region.

Throughout the study area, post glacial times saw many of the former deposits removed by the fluvial action of today's streams and rivers. Remnants of these interglacial and glacial sediments can still be viewed throughout the study area in the stream cut trenches. With a few exceptions, the courses of streams fell within the boundaries of the interglacial stream trenches (Mathews, 1978). Many of these boundaries, however, along with other stream channels are as yet buried under many of the Quaternary sediments. Table 10.1 provides a stratigraphic framework of unconsolidated deposits and a chronology of Quaternary events for the study area. For further information on surficial deposits, the reader is referred to Mathews (1978), Reimchen (1980) and Ronneseth (1983).

GROUND WATER POTENTIAL

As of 1988, approximately 900 water wells records are on file with the Provincial Government of B.C. for the area. The following information is based on a report (Ronneseth, 1983) where just over 700 water wells were investigated.

The water wells and test holes range in depth from 4 to 213 m and average 46 m deep. Of these wells about 40% are reported to be completed in bedrock, about 305 are reported to be completed in the surficial deposits and completion of the remaining 30% is not known.

Table 10.1 Stratigraphy and Pleistocene Events for the Plains Region of the Study Area

* Though it is probable that lacustrine sediments were laid down during the retreat of this ice, none have been recognized (Mathews, 1978)

** The accuracy of the dating is very subjective on dates earlier than 27,000 years B.P. The only radiometrically dated sample (up to 1978) was 27,400 to 580 years B.P. from a gravel pit near Taylor, B.C. (Mathews, 1978)

The yields of bedrock wells are known for one-quarter of the wells and range from a few pails per day to 6.3 L/s (litres per second) and average 0.63 L/s. A study of yields of bedrock wells also shows that wells obtaining water supplies from sandstone commonly produce about 50 percent more water than wells drawing ground water from shale, average 0.64 L/s and 0.44 L/s, respectively.

Well yields were reported for only 10 percent of wells completed in the surficial deposits and these range from a few pails per day up to 10.1 L/s. The wells completed in sand and gravel commonly have much higher yields, up to a maximum reported yield of 10.1 L/s, than wells completed in clay or silt with a maximum reported yield of 0.5 L/s.

POTENTIAL GROUND WATER PRODUCING REGIONS

Ground water appears favourable as a water supply source for specific regions within the study area.

Investigations to date identify certain sandstone units located in the Upper Cretaceous strata (primarily the Dunvegan Formation) which represents a bedrock aquifer with the potential of yielding up to 0.6 L/s of domestic ground water supplies (Mathews, 1955 and Callan, 1973). Other rock types which locally may have the potential to yield ground water supplies are sandstone and limestone formations such as those underlying the Dunvegan Formation. The possibility of obtaining greater quantities of ground water from the bedrock by deeper drilling should also be given consideration if other water supply options are limited.

Although the Cretaceous rocks of the study area represent potential aquifers for domestic water supplies, they are limited in their ability to meet irrigation, commercial/industrial or municipal water requirements. To fulfill such requirements would entail locating and developing a viable sand and gravel aquifer. Table 10.2 lists various unconsolidated surficial deposits found in the study area, their genetic origin, probably composition and the geomorphological feature they are normally associated with. This table has been divided into two sections; those deposits which make good aquifer materials and those which would make poor ones. The locations of these two categories can be found in Map . This map identifies potential aquifer regions as well as regions which may be sensitive to pollution sources because of the presence of overlying highly permeable materials. It should be understood, however, that these categories are general in nature and, as such, the permeability of the unconsolidated sediments can vary both areally and with depth. For example, viable aquifer sediments or conditions may be located beneath overlying low permeable materials and low permeable materials may underlie sediments which would make good aquifers.

Table 10.2 Unconsolidated Surficial Deposits