Oak Country Golf Course, De Soto, Kansas

2020

The Carpenter Dam, DJO- 0171, Dam Assessment  project identified several deficiencies and issues on this dam believed to be more than 50 years old. Recently reclassified to high-hazard due to previously identified hydrological inadequacies and downstream potential for flooding, the structure was not permitted and had no emergency plan in place. No original plans or specifications were on file with the Kansas state dam safety division. Located on a tributary to Kill Creek in Johnson County, Kansas, the dam is approximately 33 feet high and 560 feet long. Plans for the dam are not known to exist, but it is believed the primary spillway is an 18-inch diameter corrugated metal pipe attached to a 30-inch diameter corrugated metal pipe. The auxiliary spillway is located on the right abutment. Water Resources Solutions engineers’ topographic analysis, risk assessment, and field inspection in 2015 documented several issues including: improper permitting; animal damage; rutting and erosion; damage to the outlet trash rack; tree and shrub growth on the dam; road washboarding; complete submersion of the primary outlet; outlet headwall failure; insufficient grass cover on the upstream slope; unconventional geometry with potential past slide failure; and several utility encroachments. Immediate recommendations included:

► Beginning the permitting process for the dam.

► Implementing an animal-control plan, including filling large burrows on the dam.

► Repairing the headwall and void at the outlet pipe for the primary spillway.

► Repairing the trash rack on the primary spillway.

► Repairing rutting and erosion on the entrance roadway on the left abutment.

The team noted the importance of understanding that these types of issues do not get worse in a linear fashion, and therefore, accurately predicting potential failure was risky. As time goes on, the degraded conditions could accelerate and become large complicated issues in what seems to be a brief period of time. The most cost-effective approach suggested was to implement an active maintenance program, including:

► Implementing an animal control plan and filling small burrows on the dam.

► Repairing the roadway on the dam crest and adding additional gravel.

► Monitoring the seepage along the downstream toe of the dam.

► Monitoring the apparent slide on the downstream slope of the dam.

► Continuing to keep unwanted vegetation off of the dam.

► Removing the noted encroachments if determined to be detrimental to the stability of the dam or if they provided significant obstruction to flow in the auxiliary spillway