Recurring inspections by owners
In addition to the required consultant inspection and Wisconsin DNR decennial (every 10 years) inspections (high and significant hazard dams only), the owner of a dam should inspect their dam on a regular basis and after any high water event. The primary reason is to watch for changes that may indicate the need for repairs or even the existence of serious deficiencies that if left unaddressed could lead to failure of the dam.
Review the past inspection forms to see what areas of concern that other inspectors may have noted and inspect (take photos, too) of those areas first.
It is helpful to prepare an inspection route in advance to assure that every part of the dam will be observed. Make sure to record the date, time of day, weather conditions and identify all persons present on the day of the inspection. Here is a recommended sequence to assist you in your inspection:
- Crest – Walk across the crest from abutment to abutment.
- Upstream/downstream slope – Walk across both the upstream and downstream slopes in an up and down or zigzag pattern from abutment to abutment.
- Embankment–abutment contacts – Walk the entire length of the embankment–abutment contacts with natural grade (groins).
- Outlet conduit – Observe all accessible features of the outlet conduit.
- Spillway – Walk along the entire length of the spillway in a back and forth manner.
- Spillway abutments – Traverse abutments in a practical manner so as to gain a general feel for the conditions which exist along the valley sidewalls.
- 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.
- Downstream toe – Walk the entire length of the downstream toe taking into account the area downstream of the toe (maybe 20 to 50 feet downstream).
- Reservoir slopes – Scout the reservoir perimeter in an effort to develop an overall familiarity with its conditions.
- 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 and powerhouse.
Be careful out there. Personal safety is your responsibility so dress appropriately and always wear the necessary personal safety equipment pertinent to your site.
These fact sheets explain and illustrate the terms used when discussing the physical characteristics of a dam:
What to look for
The following is a list of some of the conditions a dam owner may discover. This list should not be construed as an all–encompassing last word on the problems that may be encountered.
- Structural cracking
- Animal burrows
- Excessive vegetation
- Turbid discharge
- Foundation movement
- Warning signs
- Water flowing from drains (amount and clarity)1
1 Note: The presence of cloudy water either from seepage or drain discharge should be reported to the regional water management engineer (WME) immediately.
It is important for you as the dam owner/operator to keep records throughout the existence of the dam. Accurate records can better illustrate the dynamic nature of the structure and aid those performing inspections in the future. The DNR dam safety section recommends the dam owner establish a permanent file to retain inspection records including records of actions taken to correct conditions identified in the inspections. The following items will aid you as the dam owner/operator in keeping good records.
- Inspection checklist - A convenient way of compiling inspection observations is by recording them directly onto an inspection checklist. The checklist should be attached to a clipboard and carried by the dam inspector as he/she traverses the entire structure. Copies of the checklist can be obtained by clicking here Inspection template. There should be a copy of the checklist in your inspection, operation and maintenance plan. A good practice is to draw a sketch of conditions you 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 can be vitally important. Over time, photographs serve to provide a pictorial history of the evolving characteristics of a dam. You and other inspectors often find them to be great money savers because they can illustrate that some observed conditions (seepage, foundation movement, etc.) may have existed for many years and may have reached a state of equilibrium. With this knowledge, quick and economical remedial actions can be developed and implemented if necessary. Photographs should be dated on the back and provided with brief descriptions of the locations shown in the pictures.
- Monitoring data - It may become necessary to make measurements of various items during the course of a dam inspection. This may include measurements of seepage rates, spillway discharge rates, settlement, and for some dam owners, readings from instruments such as piezometers. It is important that this data also be compiled in a systematic manner and placed in a permanent file.
- Accompany your engineer during annual inspections. Many engineers encourage dam owners or operators to accompany them, or even assist them, on dam inspections. Also, many owners accompany department engineers during their inspections. Owners can learn many things from experienced inspectors like what to look for, where to take photos, recordkeeping techniques and reading of instrumentation. In turn, experienced inspectors can gain insight into the day-to-day operation of the dam and historical concerns from someone very familiar with the dam.
- Contact information
- DNR Dam Safety
DNR Dam Safety Program, WT/3
101 S Webster St
PO Box 7921
Madison WI 53707–7921