The Province operates a network of observation wells to provide data on ground water level fluctuations and ground water quality information on developed aquifers in British Columbia. Observation well water levels are monitored using one of four methods: 1) manually with a wetted tape, 2) continuously using Steven's chart recorders, 3) electronically with data loggers or 4) remote monitoring using cellphone technology.
Water level data from observation wells are collected on a monthly basis by field observers and forwarded to Regional Offices. Data are then checked for errors and ommissions and forwarded to the Water and Air Monitoring and Reporting Section for final checking and storage. Water level data are referenced from ground level and the month end water level reading are entered and stored in Excel to produce a month-end hydrograph. The method of measurement and accuracy of each method are given below:
|Method of measurement||Accuracy|
|Wetted Tape Method||+/- 1 mm|
|Steven's Chart Recorder||+/- 1 mm|
|Data Logger||+/- 0.1 %|
Hydrograph Analysis - Observation Well 012
The graphs above show the ground water level in the well (top), the cumulative precipitation departure or CPD (middle) and the actual monthly precipitation for the Abbotsford Airport climate station (bottom). The CPD graph is a derivative of the precipitation data. The mean monthly precipitation over the study period is determined and the cumulative departures from the mean of the actual monthly amounts are plotted. CPD graphs can be useful in establishing how the ground water level in a particular aquifer responds to precipitation.
Observation well 012 is completed in the unconfined, sand and gravel, Abbotsford-Sumas Aquifer. Since 1964 the ground water level in the well has ranged from a maximum of 1.1m below ground level to a low of 7.3m below ground level. The hydrograph indicates that maximum ground water levels for this well occur seasonally during January and February and that minimum ground water levels occur seasonally during October and November. The difference between maximum and minimum ground water levels in one season ranges from 2m to 5m. The minimum ground water level in the well varies little from year to year, consistently reaching between 6.4m and 7.3m below ground level. The maximum ground water level varies considerably from year to year, ranging from 1.1m to 5m below ground level.
The CPD curve details strong seasonal and year-to-year cycles. Seasonally, December and January are high precipitation months and July and August are low precipitation months. Long-term variation is marked by years of below average precipitation between 1976 and 1980, 1985 and 1988, and 1992 to 1994. Years of above average precipitation were recorded between 1981 and 1984, and 1995 to 1999.
The hydrograph mimics the seasonal
variation found in the CPD curve, with maximum ground water levels occurring
one to two months after the high precipitation period and minimum water levels
occurring one to two months after the low precipitation period. A correlation
between ground water levels and year-to-year precipitation cycles is also evident.
The yearly maximum ground water level declined between 1976 and 1980, years of
below average precipitation, and then rose between 1980 and 1984, years of above
average precipitation. Comparison of the hydrograph and CPD curve is somewhat
erratic, but the gross relationship between precipitation and ground water levels
can still be recognized.