Iowa Administrative Code › Agency 567 - Environmental Protection Commission › Title V - Flood Plain Development › Chapter 73 - Approval, Construction, Use, Maintenance, Removal, Inspections, and Safety of Dams › Rule 567-73.19 - Hydrologic and Hydraulic Criteria

Current through Register Vol. 47, No. 3, July 24, 2024
(1)
Hydrology and hydraulic
				calculations.
Hydrology and hydraulic calculations shall be submitted
				in the design report documenting the methods and analysis followed in modeling
				software selection, inflow design hydrograph determination, and reservoir
				routing. The hydrology and hydraulics section of the design report shall
				include design references, inflow hydrograph, reservoir stage storage, and
				stage discharge curves and clearly identify peak inflows, peak discharges, and
				reservoir elevations for the design floods.
(2)
Design floods.
The
				specified freeboard design floods in the table below shall be passed without
				overtopping of the dam or the dam shall be designed to withstand such overflow.
				The specified spillway design flood in the table below shall be passed by the
				principal spillway without need for operation of an auxiliary spillway unless
				the auxiliary spillway is designed such that erosion is not expected during
				operation.
Hazard Potential
Freeboard Design Flood
Spillway Design Flood
Low Hazard
Q100
Q10
Significant Hazard
Q1000
Q50
High Hazard
Probable Maximum Flood
Q100
(3)
Precipitation amounts.
The National Oceanic and Atmospheric
				Administration's NOAA Atlas 14, Precipitation-Frequency Atlas of the United
				States, Volume 8, Version 2.0, dated 2013, shall be used for the Q10-Q1000
				frequency storm events. NOAA Hydrometeorological Report No. 51, Probable
				Maximum Precipitation Estimates, United States, East of the 105th Meridian,
				dated 1978, shall be used for the probable maximum precipitation.
(4)
Spatial and temporal rainfall
				distributions and storm durations.
The design report shall document
				the sources and methodologies for inflow hydrograph development. Distributions
				and durations that produce the highest impoundment water level shall be used
				for design.
(5)
Spillway
				discharge capacity.
The spillway discharge capacity shall be
				sufficient to evacuate at least 80 percent of the volume of water temporarily
				stored during the principal spillway design flood within ten days. If this
				cannot be accomplished, the auxiliary spillway and freeboard design flood
				routings shall be made beginning with the impoundment level at the ten-day
				drawdown elevation.
(6)
Incremental consequence analysis.
An inflow design flood based
				on an incremental consequence analysis may be developed and submitted to the
				department for review as an alternative to the design floods stated in subrule
				73.19(2). The design flood selected using incremental consequence analysis is
				the flood above which there is a negligible increase in downstream water
				surface elevation, velocity, and consequences due to failure of the dam when
				compared to the same flood without failure. If the department concurs with the
				analysis, the freeboard design storm may be reduced. The minimum design flood
				for a high hazard dam shall be Q500. The minimum design flood for low hazard
				and significant hazard dams shall be Q100.