Geoscience Reference
In-Depth Information
Environmental geotechnics in peat and
organic soils
8.1 INTRODUCTION
As described in the earlier chapters, peat lands in recent times have come to be seen as
an economic resource to be drained, cleared and then used for building and road con-
struction, agriculture or forestry. With rapid reclamation and development, some may
argue to increase attention on conserving what is left for biodiversity, water resources,
recreation and other purposes. According to Rieley (1991), peat land (lowland tropical
peat land) performs vital ecological and hydrological functions related to hydrology
(water storage, flood control and fisheries) and hydrochemistry. Andriesse (1991) listed
the ecological assets of pristine peat land, such as playing a role in the delicate hydro-
logical balance existing in the lower region of large river basin, serving as a buffer
between salt and fresh water, and absorbing heavy metals in agricultural areas fringing
the peat land. The ecological attributes and benefits derived from undisturbed peat
land are summarized in Table 8.1.
8.2 PEAT HYDROLOGY
Water plays a fundamental role in the development and maintenance of tropical peat.
An adequate supply, determined by the balance of rainfall and evapotranspiration, is
critical to its sustainability. A small change in the water level will induce a shift and
losses within the peat communities. Hydrology is the pattern of water movement. It is
vital to the functioning of the peat ecosystem. The hydrology of peat is extremely impor-
tant as an environmental determining factor for the maintenance of the peat's structure
and function. The hydrological conditions affect many abiotic factors, such as soil aer-
ation, nutrient availability and salinity, which then affect the flora and fauna. Even
though the hydrological behaviour of tropical peat is not clearly understood, rainfall
and surface topography are believed to regulate the overall hydrological characteristics
of peat land.
The peat land is purely rain-fed, thus making it an ombrogenous peat, especially
in the middle section (see Chapter 2). The water table is close to or above the peat
surface throughout the year and fluctuates with the intensity and frequency of rainfall.
The fluctuation is caused by variations in the influx and efflux of water. The effects of
precipitation on the mean annual level of the water table in the peat land depend on
the peat complex and time span considered. In the long-term, the mean annual water
