Wednesday, November 15, 2006 - 9:00 AM

Vertical and Horizontal Movement of Soil and Piezometers at a Long Term Wet Vertisol Study in Texas Gulf Coast Prairie Bottomland Hardwoods.

Amanda Bragg and Wesley Miller. USDA-NRCS, 115 Plaza Dr. #706, Kerrville, TX 78028, United States of America

Vertical (heave) and horizontal (throw) movement of soil and piezometers were measured after an eight year wet Vertisol study in bottomland hardwoods to determine if soil or piezometer movement had resulted in problems with measuring episaturation at the monitoring sites. Piezometers were originally constructed of schedule 40 PVC pipe and were placed in triplicate sets at depths of 30-, 50-, 100-, and 200-cm, with a single 500-cm deep piezometer at three nonponded and four ponded sites. Ground level was permanently marked on each piezometer. Precipitation in 2004 was abnormally high in the region which resulted in about the wettest possible field conditions when heave and throw measurements were made in June. Heave was determined by the difference between the permanent ground mark on the piezometers and surface ground level and ranged from 0- to 9-cm. Throw was determined by how much the above ground part of the piezometers was out of plumb and ranged from less than 2-cm to 5-cm. Statistical analysis indicated less heave occurred in the 30-, 50-, and 100-cm than in the 200- and 500-cm piezometers. We believe wet field conditions caused the clay to swell (heave) in the upper 50- to 100-cm, and the shallower depth piezometers moved upward with the soil. The 200- and 500-cm piezometers did not move as much because the lower portions were below the depth of major moisture changes and were anchored in dryer soil. No functional failure was found in any of the piezometers.