Experimental analysis of drainage and water storage of litter layers

Abstract. Many hydrological studies of forested ecosystems focus on the study of the forest canopy and have partitioned gross precipitation into throughfall and stemflow. However, the presence of forest litter can alter the quantities of water available for soil infiltration and runoff. Little information exists regarding the value of storage and drainage parameters for litter layers. Vegetation parameters of this kind are required in physically-based and lumped conceptual models to quatify the availabilty and distribution of water. Using a rainfall simulator and laboratory conditions two main objectives were investigated using layers of recently seneced poplar leaves, fresh grass or woodchips:

1) Effect of rain intensity on storage. With this respect we found that: maximum storage (C_max), defined as the detention of water immediately before rainfall cessation, increased with rainfall intensity. The magnitude of the increment was up to 0.5 mm kg⁻¹ m⁻² between the lowest (9.8 mm h⁻¹) and highest (70.9 mm h⁻¹) rainfall intensities for poplar leaves. Minimum storage (C_min), defined as the detention of water after drainage ceased, was not influenced by rainfall intensity. Repeated wetting-draining cycles or layer thickness have no effect on C_max or C_min.

2) The evaluation of drainage coefficient for the Rutter model. This model was found accurate to predict storage and drainage in the case of poplar leaves, was less accurate for fresh grass and resulted in overestimations for woodchips.

Additionally, the effect of an underlaying soil matrix on lateral movement of water and storage of poplar leaves was studied. Results indicated that the soil matrix have no effect on C_max or C_min of the litter layer. Lateral movement of water in the poplar layer was observed at intermediate rainfall intensities (30.2 and 40.4 mm h⁻¹), but not a the lowest or highest rates.