- Reservoir Sedimentation
- Natural Resources and Environment
- GEO 121: Earth’s Physical Environments
- GEO 242: Mapping a Changing World
- GEO 425/525: Hydrogeography
- GEO 426/526: Watershed Management
My interests are in geomorphology, water resources and environmental management. Most of my recent work has examined the impacts of historic variations in erosion rates on sediment storage and yield, and relations between land use/land management and water quality. I study these issues both at the local (watershed) scale mainly in southwestern Ohio, and at the sub-continental scale and across the United States. Locally I operate group of three stream-gaging stations in an agricultural watershed near Oxford, from which we have derived a long-term high-resolution dataset on water quality and stream flow. At larger scales my research exploits digital databases in the study of land use, hydrologic landscapes, and biogeochemical cycles. When time permits I study environmental processes from the seat of a wooden boat.
Distribution and biogeochemical impact of small water bodies in the United States.
We have identified about 2.6 million water bodies in 30-meter-resolution USGS land use/land cover (NLCD) data. About half of these are single-pixel features. A sample of 1:24,000 USGS quadrangles, which show features as small as 5 meters across, suggests a total number of water bodies >3 times greater than shown in the NLCD data. They are most heavily concentrated in the eastern Great Plains and the southeastern states, where they reach densities of over 3 per square kilometer. While this analysis does not separate natural from artificial water bodies, it is clear that the overwhelming majority are of human origin—predominantly farm ponds. These features locally elevate evaporation, divert and delay downstream water flow, and modify groundwater interactions and local biotic habitats. They apparently intercept about as much eroded soil as larger, better-documented reservoirs. Collaborators include Steve Smith (CISESE, Ensenada, Mexico), Bob Buddemeier (Univ. of Kansas), and Rich Sleezer (Emporia State Univ.).
Sediment and nutrient fluxes in an agricultural landscape.
This work focuses on movement of sediment and nutrients through the hydrologic system, and the linkages between these fluxes and reservoir ecosystems. We have been monitoring streamflow and sediment transport in the 260 km2 Upper Four Mile Creek watershed in southwestern Ohio since 1992. The watershed is >85% agricultural, and land management practices dominate material fluxes. Changing agricultural practices such as conservation tillage, nutrient management, and livestock management practices are having dramatic effects on sediment and nutrient yields from the landscape, with significant decreases in phosphorus and sediment fluxes. These changes in stream water quality are having significant effects on the ecology of Acton Lake. The project is currently funded by a NSF Long-Term Research in Environmental Biology (LTREB) grant. Collaborators include Mike Vanni and Maria Gonzalez. Stream flow data are available for streams draining to Acton Lake — contact Bill Renwick.
Sediment delivery to streams in agricultural regions of the U.S. has decreased dramatically since the mid-20th century. This decrease is a result of cessation of cropping on marginal lands, highly successful implementation soil conservation technologies, and the proliferation of artificial impoundments that trap fluvial sediment. Locally, peak stream flows have been increased by urbanization, and in some areas climate change may be increasing the magnitude and/or frequency of intense storms. As a result, streams which had been experiencing significant channel and floodplain sedimentation in the early 20th century as a result of accelerated erosion are today undergoing channel incision and erosion. In collaboration with students Monica Rakovan (Geology) and Beth Ellison (now at SIU Carbondale) I am investigating the impacts of this channel erosion on streams in the southwest Ohio region.
Ponds and reservoirs in southwestern Ohio.
Three counties in southwest Ohio–Preble, Butler, and Hamilton–represent a gradient of land use and topography within which the effects of artificial impoundments on the hydrologic landscape and biogeochemical cycling can be studied. Preble County, in the north, is relatively flat and agricultural. Hamilton County, in the south, is relatively hilly and urban (metropolitan Cincinnati) with large forest areas. Butler County is intermediate in topography and land use. In the last century several reservoirs and over 4,000 small ponds and several larger reservoirs have been built in the three-county region. Ponds are most common in Butler County, which has a large portion of land that is neither ideal for agriculture nor dense urban settlement. Ponds built in the mid-20th century served mostly agricultural purposes, but today most pond construction is associated with suburban development. Ponds are dynamic features on the landscape. The number of ponds has grown steadily, but of 835 ponds that existed in the three-county region in the mid-1950s over 90% had disappeared by 2000.
Spatial and temporal patterns in reservoir sedimentation in relation to upland erosion rates.
Reservoir sedimentation data provide an excellent tool for summarizing trends in sediment transport over long periods of time. Using reservoir sedimentation data from a variety of published sources as well as original measurements in Ohio I have investigated trends in sedimentation in relation to land use and upland erosion. Among the conclusions are: 1) Despite long-term and widespread decreases in agricultural erosion, sedimentation rates are not declining generally. 2) Continued high reservoir sedimentation rates appear to be sustained by a shift in sediment sources away from uplands and toward channel erosion. 3) Urbanization and high relief tend to enhance excavation of sediment from alluvial storages. 4) Large-scale sediment budgets suggest that total reservoir sedimentation is very large in relation to upland erosion. If confirmed this would imply that colluvial and alluvial sediment sinks are no longer dominant, and that net removal of sediment from alluvial storages is widespread.
Knoll, L. B., M.J. Vanni, W.H. Renwick, E.K. Dittman, and J.A. Gephart, 2013. Temperate reservoirs are large carbon sinks and small CO2 sources: Results from high resolution carbon budgets. Global Biogeochemical Cycles. doi: 10.1002/gbc.20020
Rubenstein, J.M., W. H. Renwick, and C.T. Dahlman, 2013. Introduction to Contemporary Geography. Prentice Hall.
Rakovan, M.T. and W.H. Renwick, 2011. The role of sediment supply in channel instability and stream restoration. Journal of Soil and Water Conservation 60: 40-50.
Dahlman, C.R., W.H. Renwick, and E.F. Bergman, 2011. Introduction to Geography: People, Places and Environment, 5th edition. Englewood Cliffs: Prentice-Hall, 595 p. (1st edition 1999; 2nd edition 2001; 3rd edition 2005; 4th edition 2008. 1st-4th editions authored by E.F. Bergman and W.H. Renwick.
Renwick, W.H. and M. T. Rakovan, 2010. Sediment supply limitation and stream restoration. Journal of Soil and Water Conservation 65:67.
Renwick W H., 2009. Lakes and Reservoirs of North America. In: Gene E. Likens, (Editor) Encyclopedia of Inland Waters. volume 2, pp. 524-532 Oxford: Elsevier.
Renwick, W.H., M.J. Vanni, Q. Zhang, and J. Patton, 2008. Water quality trends and changing agricultural practices in a Midwest US watershed, 1994-2006. Journal of Environmental Quality 37:1862-1874
Renwick, W.H., and Z.D. Andereck, 2006. Reservoir sedimentation trends in Ohio, USA: sediment delivery and response to land-use change. In Rowan, J.S., R.W. Duck, and A. Werritty (eds), Sediment Dynamics and the Hydromorphology of Fluvial Systems. International Association of Hydrological Sciences Publication no. 306, p. 341-347.
Renwick, W.H., R.O Sleezer, R.W. Buddemeier, and S. V. Smith, 2006. Small artificial ponds in the United States : impacts on sedimentation and carbon budget. Proceedings of the 8th Federal Interagency Sedimentation Conference. Paper 10A-3; 7 p.
Renwick, W.H., S.V. Smith, J.D. Bartley and R.W. Buddemeier, 2005. The role of impoundments in the sediment budget of the conterminous United States. Geomorphology 71: 99-111.
Vanni, M.J., K.K. Arend, M.T. Bremigan, D.B. Bunnell, J.E. Garvey, M.J. Gonzalez, W. H. Renwick, P.A. Soranno, R.A. Stein, 2005. Linking Landscapes and Food Webs: Effects of Omnivorous Fish and Watersheds on Reservoir Ecosystems. Bioscience 55: 155-176.
Renwick, W.H., S.V. Smith, R.O. Sleezer, and R.W. Buddemeier, 2004. Comment on “Managing Soil Carbon”. Science 305:1567c. Smith, S.V., W.H. Renwick, J. D. Bartley and R. W. Buddemeier, 2002. Distribution and significance of small, artificial water bodies across the United States landscape. Science of the Total Environment 299: 2-36.