Estimation of a global self-purification capacity index for Mountain Rivers from water quality data and hydrotopographic characteristics

A global self-purification index has been formulated for Mountain Rivers that allows comparatively to quantify the assimilation capacity of pollutants discharged on water bodies. The index takes into account the processes depending on the hydrotopographic characteristics such as velocity, flow and length of the study section as well as the available water quality information, the water quality objectives and the reactive-diffusive processes that each suffer of the parameters included. A compilation of quality modeling studies and monitoring campaigns of 10 key parameters was carried out, whose information was organized in the Information System of the Self-Depuration Capacity in rivers (SINCAP for its acronym in Spanish), which is the basis for representing the maps of self-purification. The index developed was applied to a case study at the basin level for the Sumapaz River (Colombia) with secondary information available at the Regional Autonomous Corporation of Cundinamarca (CAR). The results obtained show the importance of the hydrotopographic parameters in the capacity of assimilation of a river since its relation with the aeration and sedimentation processes could be evidenced by its torrential regime, thus having the greatest reduction in the parameters of sedimentable solids and oxygen dissolved. In the same way, in tributary sections of the upper Rio basin, high values of the Global Self-Purification Index (IGAP for its acronym in Spanish) were presented, otherwise in the lower basin where the topography is flat, thus leading to lower values of assimilation capacity.