GIS ASSESSMENT OF SPATIAL AND TEMPORAL VARIABILITY OF POND AND TERRACE CONSTRUCTION IN THE UPPER NEOSHO RIVER BASIN IN KANSAS

The Neosho River Basin in Central Kansas provides an excellent study area for the effects of soil conservation measures on soil erosion, fluvial sediment generation, and reservoir sedimentation. The conservation movement began early in many counties within the basin with county conservation districts being established from 1935 through the early 1940s to help farmers deal with the very erodible soils present in the basin. Many of the conservation practices promoted then are the same measures being used widely today (e.g. contour farming, terracing, grassed waterways, construction of ponds and lakes, etc.) with the relatively recent additions of the Conservation Reserve Program and limited or no-till agricultural practices. During the 1960s and 1970s three large reservoirs were constructed within the basin to provide flood control and more reliable water resources. The largest of these, John Redmond Reservoir, has silted in at a rate double that predicted by its original design parameters. The questions then become: Why is a reservoir silting in so rapidly in a drainage basin where soil conservation has been emphasized for 75 years? Did they simply not construct enough terraces and ponds? In this research digital orthophotos and NAIP imagery were used with GIS to quantify the numbers of ponds and terraces that are detectable within the Upper Neosho River Basin in Kansas. In a selected sub-basin historical airphotos were used to quantify changes in the numbers of ponds and terraces over time. Several conclusions can be drawn from these analyses: 1) The density of pond and terrace construction is greatest on sloping uplands above modern floodplains. 2) Many ponds but few terraces have been constructed in areas used dominantly for cattle grazing. 3) Intensive pond and terrace building began prior to 1944 and accelerated rapidly in the 1950s, 1960s, and 1970s as better earth-moving equipment became available. 4) With over 70,000 terraces and over 19,000 ponds present within the basin it is hard to fault the efforts of farmers and conservationists to slow soil erosion and sediment delivery to the Neosho River. However, it seems likely that no matter how intense our efforts to control erosion and sediment transport to river systems may be, reservoir sedimentation will continue to be a threat to our water resources.