Managed water, 1987-2005

Within the LMAV, a general consensus exists among water quality specialists that one the most cost-effective method for mitigating the agricultural NPS problems of suspended sediment and sediment-bound pollutants is the seasonal flooding of agricultural fields. Research has shown this increasingly common land management practice contributes substantially to sediment retention (Maul and Cooper, 2000; Willis, 2004) Numerous federal, state, and non-profit organizations offer landowners cost-sharing opportunities for installing water control structures, whether for water quality enhancement, waterfowl habitat, or as a post-harvest practice to control erosion. To the great benefit of the water quality community, these practices have proliferated on private lands over the past decade. DU research shows that in recent years the practice of water impoundment rose sharply in the LMAV, with up to 500,000 acres potentially flooded each winter. DU and other agencies track delivery of these water impoundment projects within their respective programs. However, DU landscape level research has identified the existence of hundreds of thousands of acres of water managed outside of any program in the LMAV that go unaccounted for in water quality planning. The spread of this practice, augmented by increasing reforestation of marginal cropland, are important factors influencing water quality in the LMAV. Quantification and spatial distribution analyses of these practices within and perhaps more importantly outside of programs relative to impaired water bodies are essential to planning efforts aimed at determining priority action areas for future projects. These private land conservation practices clearly enhance water quality, and determination of which waterbodies already benefit from them will enable the direction of limited funding to sites of greatest environmental efficacy. DU developed a geometric ratioing technique to extract and differentiate water impoundments from natural flood inundation cost-effectively using satellite imagery. Using this technique, DU acquired and analyzed satellite imagery going back 15 years, prior to widespread implementation of water impoundment practices and enrollment of significant acreages in reforestation cost-sharing programs. The dataset "Managed Water 87-05" depicts the sites where impounded water has been observed at least once over the period from the winter of 1987-88 and the winter of 2004-05. Though a field may not necessarily be flooded on an annual basis, the fact that it has been observed with impounded water suggests water management capacity exists on site.

Forest cover

Because forest cover plays such an important role in retaining sediment and nutrients and preventing erosion, an understanding of the current extent of forest cover and reforestation activities is vital to thorough water quality planning. Even though the clearing of the LMAV's forests generally occurred from the highest and driest sites to lowest and wettest, there still exist numerous highly flood prone areas and scouring riparian zones that lack soil stabilizing vegetation. Research shows that bottomland hardwoods remove and retain substantial sediment loads from overbank flood waters (Kleiss, 1996). In order to understand better where forested blocks and riparian buffers exist, DU analysts incorporated in STREAM a forest cover dataset for the entire LMAV (http://southern.ducks.org/ForestChangeDetection.php). Data were initially developed from 2001 Landsat 7 ETM+ imagery, classified to isolate forest cover, which was labeled as Mature. These data were augmented with WRP easement boundaries current as of 2004 enrollments, labeled as Reforestation. The Forest Cover data and stream networks allow evaluation of the use of vegetated stream buffers as best management practices and identify areas where these practices should be implemented or expanded.