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 272
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 272 is completed in the sand and gravel, Abbotsford-Sumas aquifer. The ground water level in the well has ranged from a maximum of 4.2m below ground level in March 1982 to a minimum of 9.4m below ground level in August 1994. The hydrograph shows that ground water levels follow a somewhat regular seasonal pattern, with maximum ground water levels occurring between December and February and minimum water levels occurring between September and October. The annual ground water maximum level is often multi-modal. The long-term trend for ground water level was downward from 1985 to 1994, followed by partial recovery during 1995 and 1996. Ground water levels in this well have been relatively stable since 1996.
The CPD curve exhibits strong annual 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 1985 and 1987, and 1992 to 1994. Years of above average precipitation were recorded between 1980 and 1983, and 1995 to 1997.
The major peaks and troughs of the
hydrograph and the CPD curve generally coincide, suggesting a good response
between local precipitation and ground water recharge to this aquifer. The hydrograph
lags the CPD curve by one to two months. The decline in ground water levels
from 1985 to 1994 coincides with a period of average or below average precipitation.
Ground water levels returned to near historic maximum levels by the end of 2000
in response to average and above average precipitation that occurred between
1995 and 2000.