at the spillway "canyon" a colorful "layer cake" appearance. Spillway chute repair Impressiveness of the 1993 geologic display aside, there was concern about the durability of the spillway in future releases. The structure and strength of the spillway's bedrock was studied to determine any necessary course of repair, reinforcement, or replacement. During the 1993 spillway release, daily photographs were taken of the rushing water at nine different locations to measure the speed of the expected head cutting. Analysis determined that the spillway could still survive 10 times the intensity of the 1993 release (the maximum the spillway was designed to release). However, the previously unexposed Roca Shale, which had demonstrated remarkable durability during the release, was expected to undergo rapid severe deterioration if left open to the effects of the Kansas climate. So, it was determined that minimal repair was to be made to the upper length of the chute. Weaker and fractured limestone shelves were grouted and then buttressed with shotcrete, and then the area was covered with terraced soil and returned to grass. Soil pH was adjusted to further protect the reburied rock. The rock formations of the lower portion were left exposed. Earthquake threat and mitigation Although Kansas is not widely known as seismically active, the Humboldt fault line associated with the Nemaha Ridge passes through eastern Kansas, and probably the most active region on the line is in the general vicinity of the lake. Studies that began in the 1980s showed that the geology of the area could potentially produce an earthquake capable of causing the dam to fail, which could risk the lives of thousands downstream in the Blue River and Kansas River valleys. To address this threat, the Army Corps of Engineers completed a project in July 2010 that reinforced the dam with more than 350 concrete walls to stop channels in the underlying karst, and equipped it with warning sensors. See also List of Kansas state parks List of lakes, reservoirs, and dams in Kansas List of rivers of Kansas References External links History of opposition to dam Old Northern Riley County map with locations of drowned towns Protected areas of Marshall County, Kansas Protected areas of Pottawatomie County, Kansas Reservoirs in Kansas Protected areas of Riley County, Kansas State parks of Kansas Dams in Kansas United States Army Corps of Engineers dams Bodies of water of Marshall County, Kansas Bodies of water