Peatland Tank Model for Evaluation of Shallow Groundwater Table Data without Height Reference from Benchmark

Abstract

Long-term monitoring of shallow groundwater table (GWT) is essential for the evaluation of hydrologic conditions of peatlands, which is meaningful for their conservation and restoration, especially in certain rural areas. Although there has been research in this field, a simple and effective method for the evaluation of GWT fluctuation has not been developed. Peatland Tank Model (PTM) is a one-dimensional water balance model that represents fluctuations of shallow GWT in peatland. The model contains several parameters, i.e., C (coefficient of GWT increase), Ai (coefficient for the size of plugholes, with i =1, 2, 3), and HAi (coefficient for the height of each plughole, i =1, 2, 3). We used PTM with 29 years’ GWT data from Ochiai, Sarobetsu Mire, northern Hokkaido, Japan. These GWT data do not have a height reference from a benchmark, so that the data have no common meaning or information in relation to the ground surface or elevation above sea level. Observation was conducted at three sites; Site D near a drainage ditch along a peat mining location; Site M at the edge of the peat mining area; and Site U in an unused area far from the drainage. A few sets of parameters were obtained on the basis of simulation results. Smaller simulation errors were attained using the PTM. The 29-year GWT fluctuations at Site D were the greatest and could be characterized by the largest parameter values. Parameter trends at three sites varied, and were able to reflect the various drainage conditions. Thus, the PTM is a promising method for the evaluation of long-term variations and site differences of hydrologic conditions in peatland.