Dams_Content Page_Routine inspections by owners

Routine inspections by owners

Dam owners need to perform routine inspections and during and following high water events – in addition to the required professional inspections and DNR decennial (every 10 years) inspections of high and significant hazard dams.

The primary purpose of routine inspections conducted by dam owners is to watch for changes that may indicate the need for repairs or deficiencies that if left unaddressed, could lead to a dam safety incident. The routine inspection process and checklist should be contained in the Inspection, Operation, and Maintenance Manual (IOM) for each dam.

How to perform a visual inspection

Dam owners need to be familiar with their dam, including the various components and terminology. Common tools to help during a routine inspection include a camera, tape measure, soil probe, and the checklist.

All parts of the dam should be observed during routine inspections, and an inspection checklist should be used to document findings during the inspection.

Understanding and using correct terminology is important when discussing and describing the physical characteristics of a dam. The common glossary of dam terms should referenced ahead of and while performing the routine inspection.

Below is a list of recommendations on how to inspect different features of a dam:

  • Crest – Walk across the crest from abutment to abutment zigzagging between the upstream and downstream shoulders.
  • Upstream and downstream slopes – Walk across both the upstream and downstream slopes in an up and down or zigzag pattern from abutment to abutment.
  • Abutments (groins) – Walk the entire length of the upstream and downstream abutments (groins) on both the left and right sides of the embankment.
  • Downstream toe – Walk the entire length of the downstream toe and the area about 20 to 50 feet beyond (downstream) of the toe.
  • Low-level outlet conduit (often referred to as a lake drain) – Observe all accessible features of the outlet conduit and look at the inside of the conduit from the downstream end, if accessible. Visually inspect all gates, stop logs, valves, and other control features of the low-level outlet conduit, as applicable.
  • Principal and Auxiliary Spillways – Walk along the entire length of the approach and discharge channels and structure as well as the spillway-embankment interface in a back-and-forth manner. If the spillway is a conduit through the embankment, inspect all visible portions of the structure including the inside of the conduits, if accessible. Visually inspect all gates, stop logs, valves, and other control features of spillways, as applicable.
  • Downstream channel – Travel the route of the stream below the dam to maintain familiarity with locations of residences and property that can be affected by operation of the dam or dam failure.
  • Any other appurtenant works – Walk around and note all other areas of the dam including but not limited to the mill race, tail race, mill race gates, canals, and powerhouse. Focus on structures that hold back water.

What to look for

The dam owner should be looking for changes to the condition of the dam, including new defects or issues, and if and where seepage is occurring. In addition, the dam owners should take readings from any gages or instruments near or on the dam.

Common changes and/or defects that may be observed at a dam include:

  • Settlement of structures or the embankment
  • Concrete deterioration (e.g., exposed rebar, spalling, cracking, etc.), joint separation and/or misalignment of concrete pipes
  • Embankment issues like cracking, slides or slumps, bulges, depressions or sinkholes, animal burrows, wave erosion, and excessive vegetation
  • Seepage or boils
  • Erosion due to surface runoff (e.g., rills and/or gullies)
  • Erosion, undermining or scour at discharge structures or in the discharge channel
  • Deterioration and operability of control structures such as gates, stoplogs, valves
  • Vandalism
  • Missing or degraded warning signs

Additional resources on how to perform dam safety inspections and what to look for are available at the Association of State Dam Safety Officials (ASDSO) resources for dam owners and operators website.

Keeping records

It is important for dam owners to keep records throughout the life of the dam. Accurate records can better document the condition of the dam overtime and aid those performing inspections in the future. DNR Dam Safety recommends that the dam owner establish a permanent file, either hard copy or electronic, to retain inspection records including records of actions taken to correct changing conditions and/or defects identified in the inspections.

The following items should be included in the permanent file:

  • Inspection checklist - Inspection observations should be documented on an inspection checklist and should be carried by the dam inspector as they traverse the entire structure. The checklist used during routine inspection should be included in the IOM.

    A good practice is to draw a sketch of the dam with measurements of the conditions observed. The sketch is intended to supplement the information recorded on the inspection checklists; however, it should never be used as a substitute for clear and concise inspection checklists.

  • Photographs - Inspection photographs are an important part of the routine inspection process as they provide a pictorial history of the evolving characteristics of a dam. At a minimum, photographs should be dated and named with a description and location of where the picture was taken.
  • Monitoring data - Instrumentation and seepage measurements should be taken during each inspection. The readings should be documented and analyzed for trends or changes in the readings. The IOM should document the process of reading and analyzing instrumentation data and seepage measurements.

Contact information

DNR Dam Safety
DNR Dam Safety Program, WT/3
101 S Webster St
PO Box 7921
Madison WI 53707–7921