SEEPAGE METER ERRORS

Although the seepage meter has been widely used in limnology, measurement errors are commonly ignored. These errors result in the need for meter correction factors due to flow field deflection and frictional resistance and head losses within the meter and prefilled bags to avoid short-term influx of water caused by the pulling action of deformed bags. Tank-test data indicate a ratio of measured to actual inseepage of 0.77 (at in-seepage rates < 20 mm h-1), with a ratio of meter to interstitial seepage flux of 0.50. Provided these precautions are observed and the adjustment factor is applied, field test ''point estimates'' of seepage inflow with replicate seepage meters generally have relative root-mean-square error(s) < 20%. Data from measurements at single locations in tank tests indicate a constant bias and show that, once installed, the actual instrument error is even less (approximately 5%). These errors are small compared to spatial and temporal components of sampling error typically encountered in the field.