The Ground Water Section of Water, Land and Air Protection operates a network of 163 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 288
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 Comox 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 288 is completed in the Hornby Island fractured bedrock aquifer (Aquifer No.438). The ground water levels ranged from a maximum of 10.7m below ground level in February 1999 to a minimum of 18.1m in September 1995. The hydrograph shows that ground water levels follow a regular seasonal pattern, with maximum ground water levels occurring during January and February and minimum ground water levels occurring during August, September and October. As shown in the hydrograph, a rising trend in ground water level is evident between from 1984 to 2000. Ground water levels in this well are also impacted by nearby domestic well pumping.
The CPD curve details strong annual and year-to-year cycles. Seasonally, precipitation peaks during the months of January and February and is lowest in September and October. Long-term variation is marked by years of below average precipitation between 1985 and 1989. Years of above average precipitation were recorded between 1980 and 1983, and 1995 to 1998.
Major peaks and troughs of the hydrograph
and CPD curve coincide, suggesting a good correlation exists between local precipitation
and recharge of this aquifer even though ground water levels are impacted by
nearby pumping. A very brief lag period is evident in which the fluctuations
in the CPD curve precede those of the hydrograph by less than one month.