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Engineer warns sediment buildup at Site 15 reduces dam storage and raises breach risk; board urged to ask NRCS for study and funding options
Summary
At a Jan. 7 joint meeting in Keosauqua, Assistant State Conservation Engineer Mark McCurdy told Van Buren County supervisors that aerated sediment at Indian Creek Watershed Site 15 has reduced flood storage and that repeated spillway use increases breach risk; he recommended the county request NRCS planning and funding identification and study Site 13.
At a Jan. 7 joint session in Keosauqua, Mark McCurdy, Assistant State Conservation Engineer, told the Van Buren County Board of Supervisors and Soil & Water Conservation District commissioners that aerated sediment accumulation at Indian Creek Watershed Site 15 has reduced the dam’s designed flood-storage capacity and increased the likelihood of a breach if current runoff patterns continue.
McCurdy said Site 15 was designed for a 100-year lifespan with a flood volume of 575.1 acre-feet. He told the board that a 2020 re-estimate found the effective flood volume had decreased by about 161.5 acre-feet and that upstream soils now generate greater runoff than anticipated, producing unusually large aerated sediment volumes for a structure that is roughly 35 years old.
He reported that three separate 24-hour rainfall incidents forced water through the auxiliary spillway and told the board that repeated use of that spillway at the structure’s age “will likely lead to a breach” over the long term. McCurdy recommended the board and the Soil & Water commissioners send a letter to the state NRCS engineer’s office requesting three items: authorization for NRCS to plan and develop mitigation alternatives for Site 15; identification of potential funding sources to offset implementation costs; and a similar study of nearby Site 13.
County officials present included Chairman Mark Meek and Supervisor Waugh; Lisa Plecker was listed as county auditor in the meeting record. The meeting record lists additional attendees from NRCS and local conservation partners but does not show a formal motion or recorded vote on McCurdy’s recommendation. The minutes state only that McCurdy made the recommendation and that the meeting adjourned at 11:32 a.m.
The county will next need to decide whether to authorize staff to draft and send the requested letter, to seek funding, or to pursue other mitigation steps. McCurdy’s recommendation would require NRCS planning approval and identification of funding sources before major work could proceed.
