Ice Drilling - Small Holes
Dianna Gielstra (Alsup) and Steve Sweet
The smallest sized hole (2 inches) we drill through the ice is to determine
the water depth at a location. Our sampling strategy was based on obtaining
samples at three specific depths along each transect. The deepest of the stations
was 118 feet, the deepest depth that the divers can safely collect sediment
samples based on the bottom time required to perform the sampling tasks. The
middle and shallow stations were at 79 and 40 feet respectively. The initial
approach was to navigate to a spot obtained from a geo-rectified bathymetry
map. Unfortunately, this approach could not be applied due to uncertainties
in the bathymetry (an offset of between 20 and 30 meters). The alternative approach
was to find the desired depths by drilling holes and measuring the water depth
using a weighted tape measure. A Kovacs auger
with a powerhead was chosen for this task. The anticipated location of the target
depth was drilled first, depending on whether the actual depth was more or less
than the target, the next place drilled was either inshore or offshore along
the transect respectively. The thickness of the ice required the use of three
3-meter lengths (flights) of drill. The hole was started using one flight, 
when
the first flight was almost to the surface of the ice, the second flight was
added, drilling continued, and the process repeated for the third flight. When
the drill penetrated through the ice, the hole was cleaned by raising and lowering
the drill until the hole was cleared of snow and ice. After debris removal the
entire drill was removed from the hole and placed on the ground.
Once the hole was drilled, a weighted tape was lowered to the bottom and the
depth read off the tape. The drilling and measuring processes were repeated
until the correct depth was located, ranging from 20 to 40 holes per transect.
Each of the locations was marked with a flag for drilling using a 10-inch Jiffy
Drill (Dianna Alsup-Gielstra and Steve Sweet) 
or a Reed Drill. All of the deepest
and middle stations for each transect were redrilled using the Reed Drill, with
the shallowest station usually being drilled using a Jiffy Drill.
when
the first flight was almost to the surface of the ice, the second flight was
added, drilling continued, and the process repeated for the third flight. When
the drill penetrated through the ice, the hole was cleaned by raising and lowering
the drill until the hole was cleared of snow and ice. After debris removal the
entire drill was removed from the hole and placed on the ground.
Once the hole was drilled, a weighted tape was lowered to the bottom and the
depth read off the tape. The drilling and measuring processes were repeated
until the correct depth was located, ranging from 20 to 40 holes per transect.
Each of the locations was marked with a flag for drilling using a 10-inch Jiffy
Drill (Dianna Alsup-Gielstra and Steve Sweet) 
or a Reed Drill. All of the deepest
and middle stations for each transect were redrilled using the Reed Drill, with
the shallowest station usually being drilled using a Jiffy Drill.