The PVC mat penetration device, Well B2, is located at Station B2 across a former open water pond from the wetland ponds restoration site at Na Pohaku o Hauwahine. The mat here is weak and readily depressed.
- The following legend and explanations apply to the graph above:
- Vertical lines "I" and "II" mark when changes were made to the water level measuring device: before I - readings from the coring device; after I - a measuring tape with brass weight used; II - tape device weight modified.
The following are all derived from measurements made with the weighted drop line. The blue circles line is height of water above a "solid" bottom. The green line represents "top of mat" calculated as tape reading from solid bottom to pipe lip, less pipe extension above mat, plus a correction (+0.05) for the effect of the observer depressing the mat. The brown line represents "bottom of mat" calculated as "top of mat" minus mat thickness. The small blue squares show the depth to solid bottom measured with the weighted line just prior to each leveling survey measurement. These depths are calculated by subtracting the drop line measurement to water level in the well from the staff gage water level reading (corrected) the same day, on the assumption that the two are identical. Vertical lines representing the PVC casing are shown at selected points in time for reference, plotted from the measurement from solid bottom to upper lip of pipe and pipe length. The casing is attached (and moves with) the marsh "surface" (green line).
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 as described elsewhere. 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 elevation measurements of the solid bottom using standard leveling survey techniques from the top 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 show consistent differences (range of 5 measurements: -0.56 to -0.92 ft; negative values imply the rod was pushed deeper into the mud than the drop line).
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Sta. GPS: Date installed: Pipe length: Ext. above mat: Mat thickness: Under mat: Soft Muck layer: Clay layer at |
June 2002 2.70 ft. 0.89 ft. 1.52 ft. (3) water 0.70 ft.(7) thick -0.28 ft. (7) elev. |
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(n) = number of independent measurements | |
Well B2 is located on the north side of an area of poor or weak mat formation covered by a monotypic stand of cattail. We believe this location is either in or near the northern margin of a former pond as depicted on the 1968 USGS Topographic Sheet (Mokapu Quadrangle; see right).
In this location, a layer of water about 1.5 feet thick lies beneath the organic (peat-vegetation) mat. The bottom appears to include a 6- to 8-inch layer of soft mud not penetrated by the drop line weight, but through which the staff settles before encountering solid bottom. The organic mat is clearly floating here, and it is difficult to make readings without noticeably depressing the mat around the well. A correction factor has been added to the drop-line readings to compensate for this temporary depression. As at Station B1, the vegetated marsh surface here maintains a relatively constant relationship to the water level and changes in water level following rainfall inputs are not exaggerated over changes recorded in the open ponds at Na Pohaku o Hauwahine. Thus, this area fits the standard floating mat model (see Well B1). However, the mat floats only about an inch or two above the water. Consequently, the material is saturated throughout and less capable of supporting repeated foot traffic.