Ecohydraulic Model for Autodepuration Assessment in River Ecosystems

Generally, biotic and hydraulic studies are conducted independently to establish a base line for river ecosystems. This paper presents an eco-hydraulic model with field validation that may provide an indirect assessment of a river auto-depuration capacity. The eco-hydraulic model integrates a hydraulic and biotic field techniques based on conservative tracer principles. The eco-hydraulic model is comprised as follows: [1] selecting a river segment length or river section; [2] running the dye-tracer technique (DT) to establish the travel time, mean velocity and flow rate: [3] running the leaf litter retentivity (LR) technique to establish retention rate and mean travel distance at three consecutive sections; and [4] post-processing of data. Preliminary tests of the proposed model in an urban creek in Bogota, Colombia shows that the DT technique is able to measure the mean velocity of the stream in short distances when two DT curves are measured. It was proven that the tree leafs are retained in the first half of each section for creeks with shallow waters and that three consecutive sections defined present an appropriate discretization of the river segment to establish a retention rate value. The water mass travel time in La Vieja creek tends to represent better the retentivity process of particulate organic matter than the arbitrary one-hour time used in the LR technique. With the proposed model is possible to obtain a retention rate of particulate matter that considers the hydrodynamic of the stream indirectly measured through a hydraulic dye-tracer technique.