Modeling of the Tidal Section of a River System by Pre-College Students Using GIS and Field Data

In July, 2002, a group of fourteen pre-college students conducted a three-day study of the tidal section of the groundwater-fed Nissequogue River system, which spans from the interior of Long Island to Long Island Sound. The students were participants in the Brentwood Honors Earth Science program, which offers rising tenth graders from the Brentwood, New York School District a four-week summer residential experience at Stony Brook University that engages them in inquiry-based studies of environmental geology. Pre- and post-tests assessed the project's effectiveness in fostering cognitive models of the system. The initial day of the project involved using GIS datasets to formulate hypotheses about the relationships between the saline water brought in by the tides, a phenomenon the students understood in a global context, the flow of freshwater, the topography, and the biota present along the riverbanks and in the surrounding uplands. Datasets included aerial photographs, digital elevation models, and shapefiles representing the coastline, water table elevations, and roads. To enhance their cognitive maps of Long Island, the students were first asked to explore the aerial photographs and road datasets to locate their school and observe its relationship to the study area. Then they used the aerial photographs, digital elevation models and water table contours to propose models of the system that could predict patterns of flow direction, salinity, fauna, and flora along the river. During a canoe trip on the second day, the students collected data on salinity, flow direction, fauna, and flora at five points along the tidal section of the river. They used printed aerial photographs to locate these data collection points. Salinity was measured with a hand-held refractometer, and fauna and flora were identified using an illustrated set of field guides to Long Island's natural environment. On the final day, the students entered their data as a new theme and analyzed it to evaluate and refine their models of the system. Discussions and pre- and post-tests involving hand-drawn maps revealed that students learned that: 1) groundwater enters the river all along its course due to gravity, 2) salinity increases towards the mouth of the river due to mixing, 3) this salinity gradient migrates dynamically with the tides, 4) species distribution reflects salinity, and 5) flow direction reverses with tide in the tidal section of the river. However, they struggled to understand that peak velocity of the ebb tide exceeds that of the flood tide in the system.