Unsaturated seepage analysis at the Guayabo National Archaeological Monument, Costa Rica

The Guayabo National Archaeological Monument is considered one of the most important historical and political ceremonial centers of pre-Columbian Costa Rica, Central America, and it depicts the ingenuity and the quality of life of Costa Rica´s inhabitants between 800 BC and AD 1400. This site was named International Historic Civil Engineering Landmark in 2009 by the American Society of Civil Engineers (ASCE). Evaluation of the unsaturated flow at the Northwestern slope using a two-dimensional model was performed. It was determined from field and modeling that at a relatively shallow depth the soil is relatively impermeable; thus, producing a large amount of run-off that tends to deteriorate the archaeological structures, and induce landslides. As part of the site investigation, exploratory borings were performed, and piezometers were installed in the upper, middle, and bottom parts of the slope. A series of laboratory testing was also performed to obtain index soil and permeability properties. The soil-water characteristic used to develop the K-Curve was also obtained. Additionally, a groundwater model was created using the geotechnical model and a water balance analysis for the area, where different scenarios of recharge and precipitation were analyzed taking into consideration the observed data. The volume of slope run-off through towards the archaeological site was estimated and the areas where it emerges, as well as the field groundwater.