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 292
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 292 is completed in an unmapped, unconfined, sand and gravel aquifer. The ground water level in the well ranged from a high of 8.9m below ground level in April of 1985 to a low of 10.6m in September of 1996. The hydrograph shows that ground water levels follow a regular seasonal pattern, with maximum ground water levels occurring during February, March and April and minimum ground water levels occurring during August, September and October. Ground water levels in this well are influenced by pumping interference from neighboring domestic wells.
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.
The major peaks and troughs of the
hydrograph and CPD curve coincide, suggesting a good correlation between local
precipitation and recharge of this aquifer. The lag between precipitation events
and the ground water level response is one to two months.