Submitted to: Geocarto International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2004
Publication Date: 12/1/2004
Citation: Webster, C.F., Fletcher, R.S., Everitt, J.H., Davis, M.R., Escobar, D.E. 2004. Assessing a wastewater discharge to the subtropical Rio Grande Valley using aerial videography and in site physicochemistry. Geocarto International. 19(4):41-48. Interpretive Summary: Environmental and water quality managers need improved methods that have potentials for detecting and assessing wastewater (pollution) discharges into rivers. Traditional boat surveys of rivers and/or large arroyos used for these purposes need to be replaced with better technology. Airborne multispectral videography, in conjunction with ground measurements (water chemistry), was evaluated for assessing a pointsource pollution discharge to the Rio Grande and tracking the discharge downstream to determine distribution and dilution of its contaminants. Video imagery clearly showed the spread of the polluted water in comparison to non-polluted water. Polluted water constituents (contents comprising the pollution) were closely associated with videographic data, suggesting that these parameters could be directly related to the polluted water. These findings indicate airborne videography is a useful tool to evaluate the qualitative chemistry of impacted waterways and should be of interest to environment resource managers
Technical Abstract: The Rio Grande contributes approximately 97% of the water used in Texas' Lower Rio Grande Valley for consumption, crop irrigation, industry, support of riparian vegetation and wildlife and for recreation. Anthro-pogenic impacts on this international river have significantly degraded both the quantity and quality of its water. The study objectives were to assess the utility of multispectral aerial videography for assessing a point-source wastewater discharge to the Rio Grande and to track the plume downstream to assess distribution and dilution of the contaminants over distance. An airborne 12-band imaging system [11 visible and 1 near-infrared (NIR) band] was used to obtain imagery of the study area while in situ physicochemical data were collected along three transects established across the river. Each transect was approximately 1 km apart. Visual observations were used to divide each horizontal transect into plume, mixing and non-plume zones. Each of the three zones was sampled along each transect. All visible image bands recorded a higher light intensity (luminance) in the plume zone than in the mixing or non-plume zones for all transects. Video data correlated best with total chlorophyllous aggregates ['CA, (chlorophyll a + pheophytin a)], followed by total suspended solids (TSS), pheophytin a, total dissolved solids (TDS) and chlorophyll a concentrations. The 720 nm band demonstrated the best overall relationship with the selected parameters, followed by the 560 nm band, and then by the 700 nm band. Overall results indicate airborne videography is a useful tool for rapid monitoring of environmental water chemistry. Development of imaging techniques to qualitatively estimate concentrations of certain constituents in impacted water columns without the need for in situ sampling may be possible.