The Dam

a1. A dam is any artificial dike, levee or other barrier, together with appurtenant works, which is constructed for the purpose of impounding water on a permanent or temporary basis, that raises the water level five feet or more above the usual, mean, low water height when measured from the downstream toe-of-dam to the emergency spillway crest or, in the absence of an emergency spillway, the top-of-dam. See the graphical demonstration of the definition of a dam.

q2. How do I measure dam height?

a2. Height of dam is the vertical dimension when measured from either the invert of the outlet pipe or, in the absence of an outlet pipe, the lowest point in the stream bed or ground surface at the downstream toe of dam, whichever is lower, to the top-of-dam. See the graphical demonstration of the definition of a dam.

q3. Do I need a permit to work on my dam?

a3. If you are performing any work outside of general maintenance (ie: light vegetation removal, clearing of debris, and filling of minor erosion and animal burrows) that affects the physical structure or performance of a dam, a permit from this office must be obtained. If you are unsure of whether or not a permit is required for the type of work that you are planning, please contact this office prior to commencement of the activities.

q4. What kind of permit do I need?

a4. A Dam Construction Permit Application is required for the following:

Construction of a new dam.
Repair, modification or rehabilitation of an existing dam.
Removal of an existing dam.

q5. What is required for a permit for dam construction, repair or rehabilitation?

a5. In addition to a completed Dam Construction Permit Application, the requirements of the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.6 Sections a-c) and (N.J.A.C. 7:20-1.7 Sections a-g) Application Stages must be met.

q6. What is required for a permit for dam removal or decommissioning?

a6. In addition to a completed Dam Construction Permit Application, the requirements of the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.7 Sections h-i) Application Stage must be met.

q7. What qualifies as a Class IV dam?

a7. A Class IV Dam must meet the following:

Drainage area must be less than 150 acres.
Dam Height must be less than 15 feet.
Dam must not have the potential to impound more than 15 acre-feet of water.
Dam must pose Low Hazard potential.
Spillway capacity must safely pass the 24-hour 100-year frequency Type III storm plus 50 percent.

The complete definition of a Class IV dam is listed in the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.8 a-4). You may also see the graphical demonstration of the definition of a dam.

q8. Are trees allowed on dams?

a8. No. Significant vegetation impedes the inspection process and can hide serious deficiencies that may be occurring at a dam. Additionally, the root structure of trees affects the structural integrity of the dam, can cause seepage pathways for water through the dam, and can cause significant section loss if uprooted. Any one of these factors alone can contribute to the failure of a dam. For a complete listing of general requirements and design criteria, please refer to the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.4 and1.9).

q9. Are dams in the Pinelands area exempt from state statutes?

a9. The Safe Dam Act grants the Department jurisdiction over dams within the pinelands region that meet the following requirements: dam height greater than eight (8) feet, reservoir greater than 100 acres in area or contributing drainage area exceeding 1 square mile. However, the Department does not regulate any dam used for agricultural purposes within the special agricultural production area (SA) within the pinelands region. Please contact this office if you are unsure whether or not a dam meets these specifications.

q10. What do the different classifications of dams mean?

a10. There are four hazard classifications of dams in New Jersey. The classifications relate to the potential for property damage and/or loss of life should the dam fail:

Class I (High-Hazard Potential) - Failure of the dam may result in probable loss of life and/or extensive property damage.
Class II (Significant-Hazard Potential) - Failure of the dam may result in significant property damage; however loss of life is not envisioned.
Class III (Low-Hazard Potential) - Failure of the dam is not expected to result in loss of life and/or significant property damage.
Class IV (Small-Dam Low-Hazard Potential) - Failure of the dam is not expected to result in loss of life or significant property damage. Dam must also meet the requirements of a Class IV dam above.

For a complete descriptions of the Dam Classifications, see the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.8).

q11. What is an Emergency Action Plan (EAP)?

a11. The purpose of an EAP is to help save lives and reduce property damage in the event of a dam failure or other uncontrolled release of water. An EAP is a formal document that:

Identifies Potential Emergency Conditions and Specifies Pre-Planned Responses.
Provides for Early Notification to Local, County and State OEM Officials.
Provides Inundation Mapping of Potentially Flooded Areas.

q12. What dams require Emergency Action Plans (EAPs)?

a12. All Class I (High-Hazard Potential) and Class II (Significant-Hazard Potential) dams require Department-approved Emergency Action Plans (EAPs). It is the responsibility of the owner of the dam to review and update the EAP annually. See the Guidelines for Developing an Emergency Action Plan for additional information.

q13. What are dam inspections?

a13. Dam Safety Inspections are intended to identify conditions that may adversely affect the safety and functionality of a dam and its appurtenant structures; to note the extent of deterioration as a basis for long term planning, periodic maintenance or immediate repair; to evaluate conformity with current design and construction practices; and to determine the appropriateness of the existing hazard classification. For addition information regarding the different types of dam inspections and a standard regular inspection checklist, please see the Inspection Guidelines.

q14. How often are dams required to be inspected?

a14. The inspection requirements depend on the size and hazard classification of the dam:

Dam Size/Type

Regular Inspection

Formal Inspection

Class I Large Damannuallyonce every 3 years

Class I Damonce every 2 yearsonce every 6 years

Class II Damonce every 2 yearsonce every 10 years

Class III Damonce every 4 yearsonly as required

Class IV Damonce every 4 yearsonly as required

For complete inspection and operating requirements for dams, see the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.11).

q15. What is an Operation and Maintenance Manual (O&M)?

a15. An Operation and Maintenance Manual (O&M) is a formal document that provides guidance and instruction to project personnel for the proper operation and maintenance of the reservoir and dam. All dam owners are required to develop and use a Department-approved O&M. For additional information regarding the O&M, see the New Jersey Dam Safety Standards (N.J.A.C. 7:20-1.11) and the Sample Operation and Maintenance Manual.

Union Mill Lake

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The Dam

UnionMillLakeCC@gmail.com