Small Dam Drainage with Nonwoven Geotextile after 40 Years of Exploitation

Synthetic materials such as nonwovens, mats and membranes have been commonly used in civil engineering for many years. The changes of geotextile characteristics in time (permeability, porosity, etc.) are poorly understood. Many authors have presented the changes in the properties of synthetic materials, mainly based on laboratory tests. The studies on geotextile samples taken from working hydraulic structures are not so many. Over 40 years, the reduction in the permeability of nonwoven geotextile was about four-fold. Probably the reason for that reduction is mechanical clogging caused by fine particles which have moved from the earth dam soil to the nonwoven geotextile. Over 40 years of operations, despite the reduction in permeability of the nonwoven geotextile, the drainage worked properly. The experiment was conducted in the field and laboratory and a two-dimensional numerical model built in software package HYDRUS (two-dimensional/three-dimensional (2D/3D)) Standard was proposed. The field measurements allow calibration and validation of the numerical model. The conducted simulations showed that at a maximum water level in the reservoir equal to 3.32 m, the water supply to the drainage is higher from upstream than from downstream. Particularly, water supply from above to the drainage is absent.