The PVC mat penetration device, Well A2 at Sta. A2, is located east of the open water ponds restoration site at Na Pohaku o Hauwahine. The vegetation in this area is dominated by maile pilau, para grass, and small, disconnected patches of cattail. Note staining on outside of pipe caused by long wet season period of flooded ground.
- The following legend applies to the graph for Well A2 above:
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The following are all derived from measurements made with the weighted drop line.
Heavy blue line is the measured height of water above "solid" bottom. The wide green line represents "top of peat mat" calculated as tape reading from solid bottom to pipe lip, minus pipe extension above mat. The dashed brown line represents approximate bottom peaty layer calculated as "top of mat" minus depth to change in nature of the peaty muck. The small blue squares show the depth of solid bottom measured with the weighted line just prior to a leveling survey measurement. The elevation of these points is calculated as the difference between the recorded water level (at Na Pohaku) minus the drop line measurement of water level in the well.
The following plots are from measurements made at the the water level staff gage or by stadial survey from the staff gage. The fine dashed line is the water level recorded at Na Pohaku o Hauwahine, corrected to a USGS gage located elsewhere in the marsh. All other well measurements are corrected by the same factor as appropriate, although a method of matching the water level at the well and the "marsh" water level is still being developed. The maroon points represent actual elevation measurements of the solid bottom from standard leveling survey techniques using the elevation of the WL gage as the "back sight." Water level in the well read on the survey rod is compared with water level measured with the drop line, and these show poor agreement at this location (range of 2 measurements: 1.77 to 1.80 ft) as explained below.
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Sta. GPS: Date installed: Pipe length: Ext. above mat: Mat thickness: Under mat: Clay layer at |
--- Sep. 11, 2002 --- 0.96 ft 1.52 ft. (3) mud +1.21 ft. (10) |
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(n) = number of independent measurements |
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The marsh surface/vegetation mat at this location does follow the "Wet Meadow Model" fairly well (compare with Well A1). The larger rainfall events (October 15 and February 14) produced a rise in the aquifer with an accompanying rise in the mat surface on the order of 6 inches. It is not known if the sudden rise in the mat represents expansion of the peat or an injection of water or mud slurry beneath the mat. However, to date there is no evidence of a layer of water beneath this station. However, as the water level in the marsh continued to rise in response to rainfall and runoff inputs, water eventually ponded on the vegetated surface around the well. The marsh surface has remained relatively stable, suggesting this location generally fits our expectations for the wet meadow model.
At the times when water was exposed on the surface around this well, the water level level inside the pipe usually did not match the level outside the pipe.
Elevation measurements surveyed in with a leveling rod are initially variable, then settle down to a relatively constant value as with Well A1. This effect may represent initial tamping down of the upper surface of the clay with the rod (that is, an effect of the measuring process). Overlaying the clay layer is a layer of "muck" through which the rod penetrates but the drop line does not. This layer appears variable, and interacts with our estimate of the mat thickness, suggesting no intervening layer of water prior to February 14, and possibly only a very thin one after that time.