BOARD01548

• Board Meeting Date: 1/25/2005
• Description: Proposed Revisions to the Rules and Regulations for Dam Safety and Dam Construction
• Board Meetings - Doc Type: Memo

4.2.10 "Engineer" means a Professional Engineer registered and licensed in Colorado in
accordance with section 12-25-101, C.R.S.

4.2.11 "Enlargement of an Existing Dam or Appurtenant Structure" means any
alteration, modification, or repair that increases the jurisdictional height and/or reservoir
capacity of a dam as defined in Rule 4.2.4 and 4.2.18.

4.2.12 "Freeboard" means the vertical dimension between the crest (or invert) of the
emergency spillway and the crest of the dam.

4.2.12.1 "Residual Freeboard" means the vertical dimension between the
maximum water surface elevation at the peak of the inflow design flood and the
lowest point on the crest of the dam at which the dam would be first overtopped.

4.2.13 "High Water Line" is the water surface elevation of the reservoir at the crest (or
invert) ofthe emergency spiIlway, or, ifno emergency spillway exists, at the crest of the
dam.

4.2.14 "Impound Water" means to accumulate water in a reservoir for immediate or
future use, including the purpose of flood control and detention.

4.2.15 "Incremental Damage Analysis" means a comparative study of two floods of
differing magnitude used to identify differential impacts for loss of human life and property
damage in the zone above the lesser magnitude flood (incremental zone).

4.2.16 "Inflow Design Flood" means the flood hydrograph used to determine if the
emergency spillway's hydraulic capacity meets safety standards, the required magnitude of
which is defined by these Rules and Regulations.

4.2.17 "Jurisdictional Height" means the vertical dimension measured from the elevation
ofthe lowest point of the natural surface ofthe ground, or from the invert of the outlet pipe
if excavated below the natural surface of the ground, whichever is lower, where the low
point occurs along the longitudinal centerline of the dam, up to the spillway crest of the
emergency spillway. For existing dams, the jurisdictional height shaH be measured by
using the slope of the downstream channel and the height of the dam at the downstream toe
by extrapolating the measured height to the longitudinal centerline of the dam. The formula
for determining the vertical height of existing dams is: h = hd-fb-sl; where h = jurisdictional
height, hd = height of dam from downstream toe, fb = freeboard, s = slope of the natural
surface ofthe ground downstream of the dam, and I = measured or computed horizontal
distance between the downstream toe and the longitudinal centerline of the dam. The State
Engineer shall have final authority over determination of the height of the dam (see Figure
2).

4.2.18 "Natural Surface of the Ground" means the undisturbed ground surface before
excavation, or the undisturbed bed of a natural watercourse.

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