Included in the Kansas River corridor study area are 1,700 square miles (4,400 km2) that includes all or part of six of the 10 largest cities in the state. Based on the 1990 census, the 10 counties adjacent to the Kansas River have a combined population of 960,420, or about 39 percent of the Kansas population. Today the population of these 10 counties is estimated to be about 40 percent of the state's total. Most growth occurred in Johnson County with Douglas, Leavenworth, Shawnee, and Riley counties showing substantial gains.
The most extensive land cover in the corridor area is grassland with a coverage of 45 percent, followed by cropland at 28 percent coverage. Grassland and cropland also are the two most widespread land covers in the floodplain as well; however, cropland is predominant covering 60 percent of the floodplain area while grassland is a distant second with 14 percent coverage. The combined categories of commercial/industrial and residential, which include most of the developed area's cover, represents 7 percent of the floodplain and 9 percent of the corridor area.
The river valley averages 2.6 miles (4.2 km) in width over its 138-mile (220-km) length. The widest stretch of the river valley is between Wamego and Rossville, where it is up to 4 miles (6.4 km) wide in places, with many locations from its source to Eudora being 3 miles (4.8 km) wide. In these wide areas, geologic units dominated by shale are present in the valley walls. Below Eudora, the valley narrows significantly to less than 1.5 miles (2.4 km) and in parts of this stretch the valley is 1 mile (1.6 km) or less in width. This reach of the river appears to be confined by thick limestone units in the valley walls. Although the Kansas River follows a sinuous path, it seems to prefer the south side of the valley, impinging on the south valley wall at numerous places between Junction City and Lawrence. This could be influenced by more tributaries entering the Kansas River on the north side in this reach of the river.
Since the time of the Kansan glacier, about 600,000 years ago, the Kansas River has deepened its valley, cutting into bedrock during times of high flow. This is followed by partially filling up of the valley by depositing sediment during times of low flow. The result today is a deep bedrock trench of varying depth that contains the Kansas River and its alluvial sediment.
As the name implies, the modern floodplain is formed at times of flood when the river spreads beyond its banks across the valley floor. When it does so it carries sediment and, as the flood subsides, a sheet of fine sediment is left in its wake. These overbank flood deposits are often composed of fine silts and clays, especially when deposited some distance from the river channel. This accounts for the fine-grained alluvial sediments in the upper part of the floodplain overlying the coarse-grained alluvial deposits that were formed by the lateral migration of the river.
Most of the river sand has its source in the glacial sediments of the lower Kansas River basin and in the Ogallala Formation in the upper part of the basin. Quartz is a major mineral component of granitic rocks, which are common in the Rocky Mountains and the Canadian Shield. These areas are the ultimate sources of most of the Kansas River sand. The erosion of the Rocky Mountains by streams flowing out of the mountains and dissipating on the Great Plains formed the Ogallala Formation; the Kansan glacier with its accumulation center near Hudson Bay and grinding trek across southern Canada and the northern United States left the Kansas glacier drift in its wake. These deposits, the Ogallala and the glacial drift, are the source of much of the coarse sand that ultimately ended up in the Kansas River and its floodplain.
The Kansas River is the major source of sand and gravel for northeastern Kansas. Sand and gravel is obtained either by river or floodplain dredging. The river dredges produce some of the best-quality and least-expensive sand in the United States. In October 1997, nine dredges operated in the Kansas River, all on the middle and lower portion of the river where conditions normally favor river dredging. In 1996, Kansas River dredges produced nearly 2.4 million tons of sand and gravel that generated nearly $357,000 in sand royalties to Kansas with the value of that sand totaling about $8 million. In addition, seven floodplain or pit dredges operate within the Kansas River floodplain.
In general, the lower portion of the Kansas River (below Topeka) favors river dredging while the upper portion of the river favors pit dredging. The broader floodplain, the lower price for land, thinner overburden, and thick usable sand and gravel deposits are factors favoring pit dredges along the upper part of the river. Scarcity of land due to the narrow floodplain and commercial/industrial development, and significant overburden thickness relative to the thickness of available sand and gravel are the major reasons river dredges are preferred in the lower part of the Kansas River. In addition, more dense population in the lower reaches of the river with resulting numbers of citizens expressing concerns about extractive industries to their county commissioners is another problem in locating on the floodplain below Topeka. Normally, a river dredge requires about 10 acres (4 ha) of land for the processing plant. By contrast, a pit dredge needs about 100 acres (40 ha) of land for the plant, dredging acreage, and land for overburden stockpiles. In the heavily populated, industrialized, and extensively farmed lower portion of the Kansas River, finding a 100-acre (40-ha) tract with both good reserves of sand and gravel and little overburden that is acceptable to the citizens of the area would be very difficult. Studies along the entire river floodplain, based on physical limitations alone, have identified 74 potentially profitable pit-dredging locations, with 49 of the 74 in Pottawatomie, Wabaunsee, and Shawnee counties.
It is normally more expensive to produce sand and gravel from a pit dredge relative to a river dredge. The amount and price of land required, and the expense and removal of overburden down to the water table, costs approximately $1.00/cubic yard, before the dredge can be moved into place and begin operating. Larger areas of a pit-dredging operation will need reclamation under present state laws.
To minimize potential damage that might be caused by a substantial lowering of the bed elevation in the Kansas River, the U.S. Army Corps of Engineers placed restrictions on the amount of sand and gravel that is allowed to be dredged from certain river reaches and within 15-mile (24-km) zones along the river. This plan was phased in gradually between 1991 and 1994. With channel disturbances caused by major flood conditions during 1993, it is too early to determine whether these restrictions are correct or whether they will require future adjustment. River profiles obtained during 1992 and 1995 show an overall increase in the river-bed elevation. The restricted production on the Kansas River of sand and gravel in the Kansas City area has been offset to a large extent by dredging activities in the Missouri River, but the latter product contains a small amount of lignite, resulting in sand of a lower quality than Kansas River sand.
The present arrangement of river and pit dredges appears adequate to meet demands for sand and gravel from the construction industry for the near term. Use of alternate sources, such as sand from the Kansas River tributaries, Arkansas, or Missouri rivers would result in increased sand and gravel prices because of larger transportation costs that average $0.10 per ton mile. A scenario of no river dredging with only pit dredges on the Kansas River floodplain also would increase sand prices, particularly in the lower portion of the Kansas River where demand is highest and potential pit-dredge locations scarce.
Population trends show a long-term demand for both sand and gravel and crushed stone aggregates. Between 1980 and 1996, the population of Kansas increased by nearly 9 percent, but the population of the 10 counties bordering the Kansas River increased by nearly 20 percent. Furthermore, population projections suggest that by the year 2025, nearly half of the Kansas population will reside in the 10 counties along the Kansas River. Planners and decision-makers need to ensure that adequate, long-term supplies of sand and gravel and crushed stone are available to meet future demands for aggregates along the Kansas River corridor.
In general the channel of the Kansas River is in equilibrium or slightly degrading, that is, being deepened by erosion. However, bedrock in the channel bottom and gravel beds that are too coarse to be moved under current hydrologic conditions can prevent bed degradation. The slack water areas behind Bowersock dam and the Johnson County water intake, and the reach closest to the confluence with the Missouri River where the stage of the Missouri River controls the flow in the Kansas River, are areas of quiet water and potential aggradation, or deposition. These same features also prevent any downstream degradation from proceeding upstream.
The sediment-carrying capacity of the river and the maximum transportable grain size are functions of precipitation, sediment supply, channel characteristics, and velocity of the water. Since all of these parameters are highly variable, the sediment-carrying capacity is also highly variable. By developing an empirical relationship between sediment discharge and water discharge, Simons et al. (1984) estimated that the river was carrying about 1.67 million tons of sand per year at the De Soto gaging station. However, analysis of the data show that for any water discharge the sediment discharge varies over two orders of magnitude. Therefore, predictions of sediment-carrying capacity are subject to significant uncertainty that should be taken into account when making decisions and considering alternative policies based on the bed-load quantities.
An analysis of the maximum transportable grain size shows that the river normally transports sand-sized and finer sediments. Gravel is only transported during floods. The bed material of the Kansas River is remarkably homogeneous along the entire length and the mean grain diameter of 0.4 to 2.0mm is almost a perfect match with the medium sand range of the Unified Soil Classification.
Major floods are short-duration, high-flow events that create disequilibrium in the channel by transporting more sediment, transporting larger grains sizes, and causing changes in channel morphology (degradation/aggradation, bank erosion, and meander cutoffs). After a major flood, a gradual adjustment process tends to create a new equilibrium between the river morphology and the current hydrologic regime. However, the time scale of the adjustment can be one or two orders of magnitude larger than the duration of the event. Simons et al. (1984) determined that at the time of their analysis, the river was still recovering from the changes associated with the 1951 flood.
The 18 reservoirs in the Kansas River drainage basin, designed primarily for flood control, change the flow distribution by decreasing the frequency of very high and very low flows, while increasing the frequency of occurrence of the intermediate discharges. The reduction of the high-flow frequencies decreases the sediment-carrying capacity and maximum transportable grain size. Additionally, reservoirs trap upstream sediment and release clear water, which causes bed degradation and bank erosion downstream of the dam. Currently, the latter effects are mostly confined to those tributaries that are dammed.
The availability of sediments of a certain size and the ability of the river to transport them constrains the dredging activities in the Kansas River. Currently, the dredges are removing sand and gravel; however, incipient motion calculations demonstrate that gravel-sized material can not be transported by the river under present hydrologic conditions, except during large floods. Hence the gravel and some coarse sand currently being mined at select locations are part of ancient deposits and will not be replenished when exhausted.
A sediment budget is needed to understand the future effects of dredging in the Kansas River. This budget considers the sediment inputs and outputs along key reaches. Applying this approach to the Kansas River is straightforward, because the river is now generally at or near equilibrium. In a reach where incoming and outgoing sediment discharges are approximately equal, an additional extraction via dredging means a decrease in sediment inventory in that reach and further degradation. In this case, the annual streambed degradation can be readily evaluated as a function of the yearly extraction rate.
The same sediment budget can be applied to the entire river. The backwater effect caused by high water levels in the Missouri River creates a reach with velocities so low that even fine sediment cannot be transported. Maintaining the current channel would require that incoming sediment be removed by dredging. In the absence of dredging, aggradation would occur in part of this reach.
The key to assessing change in fluvial systems is to gather the critical information by way of a designed monitoring program and to use these data in an adaptive management strategy where a prescribed amount of degradation/bank erosion would trigger appropriate measures. Such an adaptive management strategy is appropriate for dealing with fluvial systems that are constantly adjusting to changes, allowing for the management of individual dredging permits based on site-specific information.
The above hydrologic observations are qualitative and pertain to the river as a whole. Studying specific reaches of the river requires additional data including extensive hydrographic surveys and periodic sampling of sediment discharge. Such information is necessary to assess the system response on a continuous basis. An initial assessment would provide a baseline condition against which further change can be compared. A program of such scope is not currently in place. Periodic monitoring is only being conducted near active dredging operations.
Next Page--Appendix A