Simulating the effects of water infiltration through the bottom of ditches on a shallow watertable in a Mediterranean catchment
Abstract
Catchments in the Mediterranean area often exhibit dense networks of ditches that were created to drain water in excess at the field scale. These ditches are also preferential zones of surface water percolation, and thereby of pollutant transport, to shallow watertables. This study aimed at evaluating a Richard’s based modelling approach to simulate water infiltration in the bed of a ditch and its effect on the level and shape of a shallow watertable. The study site site is a 10 m long ditch, 1 m wide and 0.8 m deep, located in the Roujan catchment (43°30' N, 3°19' E), in south-France. An infiltration experiment was conducted during 10 hours when the watertable was intially at a depth of almost 2 m below the soil surface. Networks of piezometers and tensiometers allowed to monitor the evolution of watertable levels and soil potential along three transects perpendicular to the ditch. HYDRUS 2D (Simunek et al., 1999, user’s manual International GroundWater Management Center) was used to simulate the experiment. The field observations indicated two major points. The infiltration rates were rather large and induced a significant evolution of the watertable shape and height. During the period infiltration, a sediment seal formed on the bed of the ditch, which restricted infiltration through the bed of the ditch in comparison to that through the walls. Several simulations were performed to evaluate different scenarios concerning the layering of soil hydraulic properties in the soil and at the interface between the soil and the ditch,. The scenario, which allowed the best simulation of infiltration rates and watertable levels changes, ascribed specific properties to the bed and the wall of the ditch and took into account their evolution with time due to sedimentation processes. This indicates that the hydraulic properties of the ditch-soil interface should be explicitly taken into account for simulating transmission losses in ditches
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....13863L