Code of Maine Rules › 01 - DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY › 001 - AGRICULTURE - GENERAL › Chapter 375 - DETERMINATION OF SAFETY AND SUFFICIENCY OF DAM OR RESERVOIR › Section 001-375-4 - Definition of "Unsafe and Insufficient"

Current through 2024-29, July 17, 2024
A dam or reservoir shall be declared to be "unsafe" or
				  "insufficient" if the Inspector of Dams, after utilizing all available data and
				  testimony and making appropriate calculations using known values or reasonable
				  assumptions, finds that the dam or reservoir does not meet minimum performance
				  criteria appropriate to the facility. The types of performance features that
				  should be evaluated are listed below:
A. Forces acting on the dam and evidence of
				horizontal translation that suggests there is too much force acting at any time
				against the facility;
B. Evidence
				of large total or differential deformation;
C. Evidence of slumps or bulges on the faces
				of the dam; an end-of-construction or steady state factor of safety against
				shear sliding and the factor of safety under conditions of reservoir drawdown
				and during appropriate earthquake loading;
D. Evidence that the phreatic surface within
				the dam during the full reservoir condition exists on the downstream face of
				the dam except through properly designed drains; evidence of bulges, seeps, or
				soft zones on the downstream face of the dam or on the immediate. abutments;
				evaluation of the effective stress within the dam;
E. Evidence that the dam is experiencing
				internal erosion of dam material or that the dam abutments or foundation could
				be subject to piping; an evaluation of internal drain design; an evaluation of
				seepage gradient within the dam;
F.
				An evaluation of the quantity and quality of seepage through the dam
G. An evaluation of whether a dam or
				reservoir is safe from runoff overtopping that could wash out the containment
				structure. In making this evaluation, the inspector shall consider whether the
				dam can safely sustain overtopping by the appropriate design storm, and if not,
				whether an emergency spillway is present. In appropriate cases where it is
				determined that an emergency spillway should be present, and only one spillway
				exists, the principal spillway may be considered to serve as an emergency
				spillway, provided that the principal spillway is large enough so that it
				cannot be blocked by driftwood and other floating or suspended debris. For each
				class of structure identified in paragraphs (1), (2) and (3), the inspector
				shall consider whether an emergency spillway is able to transmit without
				erosion,, or whether the dam can retain its integrity during overtopping, a
				storm of the frequency specified
(1) For
				class "a" structures, which are located in rural, agricultural, or urban areas
				dedicated to remain in flood tolerant usages where failure may only damage
				non-residential buildings, agricultural land, floodplains, or township and
				country roads: 25-year storm or flood;
(2) For Class "b" structures, which are
				located in predominantly rural or agricultural areas where failure may damage
				homes, industrial or commercial buildings, highways or railroads, or where
				failure may cause interruption of use or service of utilities: 100-year storm
				or flood;
(3) For Class "c"
				structures, where failure may cause loss of life: maximum probable
				flood.