Alternate Methods of Stabilizing Degrading Stream Channels in Western Iowa, Phase I, HR-208, 1980

Since the beginning of channel straightening at the turn of the century, the streams of western Iowa have degraded 1.5 to 5 times their original depth. This vertical degradation is often accompanied by increases in channel widths of 2 to 4 times the original widths. The deepening and widening of these streams has jeopardized the structural safety of many bridges by undercutting footings or pile caps, exposing considerable length of piling, and removing soil beneath and adjacent to abutments. Various types of flume and drop structures have been introduced in an effort to partially or totally stabilize these channels, protecting or replacing bridge structures. Although there has always been a need for economical grade stabilization structures to stop stream channel degradation and protect highway bridges and culverts, the problem is especially critical at the present time due to rapidly increasing construction costs and decreasing revenues. Benefits derived from stabilization extend beyond the transportation sector to the agricultural sector, and increased public interest and attention is needed.

Deterioration of Iowa Highway Concrete Pavements: A Petrographic Study, HR-1065, 1999

Major highway concrete pavements in Iowa have exhibited premature deterioration attributed to effects of ettringite formation, alkali-silica expansive reactions, and to frost attack, or some combination of them. These pavements were constructed in the mid- 1980s as non-reinforced, dual-lane, roads ranging in thickness between 200 mm and 300 mm, with skewed joints reinforced with dowels. Deterioration was initially recognized with a darkening of joint regions, which occurred for some pavements as soon as four years after construction. Pavement condition ranges from severe damage to none, and there appeared to be no unequivocal materials or processing variables correlated with failure. Based upon visual examinations, petrographic evaluation, and application of materials models, the deterioration of concrete highway pavements in Iowa appear related to a freeze-thaw failure of the coarse aggregate and the mortar. Crack patterns sub-parallel to the concrete surface transecting the mortar fraction and the coarse aggregate are indicative of freeze-thaw damage of both the mortar and aggregate. The entrained air void system was marginal to substandard, and filling of some of the finer-sized voids by ettringite appears to have further degraded the air void system. The formation of secondary ettringite within the entrained air voids probably reflects a relatively high degree of concrete saturation causing the smaller voids to be filled with pore solution when the concrete freezes. Alkali-silica reaction (ASR) affects some quartz and shale in the fine aggregate, but is not considered to be a significant cause of the deterioration. Delayed ettringite formation was not deemed likely as no evidence of a uniform paste expansion was observed. The lack of field-observed expansion is also evidence against the ASR and DEF modes of deterioration. The utilization of fly ash does not appear to have affected the deterioration as all pavements with or without fly ash exhibiting substantial damage also exhibit significant filling of the entrained air void system, and specimens containing fly ash from sound pavements do not have significant filling. The influence of the mixture design, mixing, and placing must be evaluated with respect to development of an adequate entrained air void system, concrete homogeneity, longterm drying shrinkage, and microcracking. A high-sand mix may have contributed to the difficult mixture characteristics noted upon placement and exacerbate concrete heterogeneity problems, difficulty in developing an adequate entrained air void system, poor consolidation potential, and increased drying shrinkage and cracking. Finally, the availability of moisture must also be considered, as the secondary precipitation of ettringite in entrained air voids indicates they were at least partially filled with pore solution at times. Water availability at the base of the slabs, in joints, and cracks may have provided a means for absorbing water to a point of critical saturation.

08005-002 Silver Lake Watershed Final Report

Silver Lake is located in an 18,053-acre watershed. The watershed is intensively farmed with almost all of the wetlands being previously drained or degraded over the last 50 years. Silver Lake is listed on the State of Iowa’s impaired water bodies list due to sediment and high nutrient level. Silver Lake is also known be in the bottom 25 percentile of Iowa’s lakes due Secchi disk readings and Chlorophyll a level. Farming in the watershed is the principle concern and cause for many of the problems occurring in Silver Lake currently with 78% of the watershed being intensively farmed. There are two major drainage ditches that have been used to drain the major wetlands and sloughs that, at one time, filtered the water and slowed it down before it reached Silver Lake. With these two major drainage ditches, water is able to reach the lake much faster and unfiltered than it once did historically. The loss of 255 restorable wetland basins to row crop production has caused serious problems in Silver Lake. These wetland basins once slowed and filtered water as it moved through the watershed. With their loss over the last 50 years that traditional drainage no longer occurs. We propose to create a Wetland Reserve Program incentive project to make WRP a more attractive option to landowners within the watershed. The incentive will be based on the amount of sediment delivery reduction to the lake, therefore paying a greater payment for a greater benefit to the lake. The expected result of this project is the restoration of over 250 acres of wetland basins with an associated 650 acres of upland buffers. The benefit for these wetlands and buffers would be reduced sediment, reduced nutrients, and slowed waters to the lake.

07025-010 College Creek Watershed Final Report

With this application, the College Creek sub-watershed in Ames represents both regional collaboration and locally directed action to improve an Iowa watershed. Already completed watershed assessment identified more than 4000 tons/yr of sediment delivered from within the Ames city limits due to degraded stream conditions. The water quality enhancement goal of this project is reducing sediment delivery specifically from unstable streambanks and degrading stream channels on College Creek, one of 4 Ames tributaries to Squaw Creek. The project will also redirect urban storm water runoff into engineered infiltration systems, intercepting it from storm drains entering College Creek. This application builds on storm water runoff demonstration projects and research already funded in the College Creek sub-watershed by EPA Region 7 and Iowa DNR. Public outreach, one of the key elements of this project, is built into every phase from engineering design feedback to construction. Innovative neighborhood learning circles are utilized to educate residents and share public feedback with project engineers to ensure that project elements are both technically appropriate and socially acceptable. All practices proposed in this project -stream stabilization, storm water infiltration, and neighborhood learning circle techniques-have already been successfully demonstrated in the College Creek sub-watershed by the City of Ames in partnership with Iowa State University.