Hydrology: Difference between revisions
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==Hydrologic Design Criteria== | ==Hydrologic Design Criteria== | ||
“Selection of an [[Inflow Design Flood]] (IDF) for a new dam or a dam undergoing significant modifications should taken into account both current conditions and reasonably anticipated future development. Development within the upstream watershed can cause increased runoff and peak flows, while development within the downstream inundation area can alter [[Hazard Potential Classification|hazard potential classification]] and specific estimates of consequences of hydrologic events… When the cost of more detailed methods such as incremental [[Consequence Analysis|consequence analysis]], a site-specific probable maximum precipitation study, or risk-informed hydrologic hazard analysis is prohibitive, prescriptive IDF criteria for High, Significant, and Low Hazard dams are recommended”.<ref name="FEMA94" /> | “Selection of an [[Inflow Design Flood]] (IDF) for a new dam or a dam undergoing significant modifications should taken into account both current conditions and reasonably anticipated future development. Development within the upstream watershed can cause increased runoff and peak flows, while development within the downstream inundation area can alter [[Hazard Potential Classification|hazard potential classification]] and specific estimates of consequences of hydrologic events… When the cost of more detailed methods such as incremental [[Consequence Analysis|consequence analysis]], a site-specific probable maximum precipitation study, or risk-informed hydrologic hazard analysis is prohibitive, prescriptive IDF criteria for High, Significant, and Low Hazard dams are recommended”.<ref name="FEMA94" /> | ||
The applicability and acceptability of various hydrologic methods varies widely across the US. Familiarity with the primary runoff generating mechanisms based on the geology, topography, meteorology, and seasonality of the region are paramount to inflow design flood determination. Guidelines and regulations related to hydrologic methods and the inflow design flow also vary based on regulatory jurisdiction. | |||
==Types of Evaluations== | ==Types of Evaluations== | ||
Revision as of 21:36, 16 March 2023
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Hydrology is essential not only in the design of a dam, but also in the feasibility study of a dam as well as in assessments of the dam into the future as the state-of-the-practice evolves. The three main components of flood hydrology, according to the United States Bureau of Reclamation (USBR) are “(1) hydrometeorology related to probable maximum precipitation determinations, (2) probable maximum flood hydrograph determinations, and (3) statistics and probabilities relating to the magnitude and frequency of flood flows”.[1]
“One of the most common causes of dam failures is the inability to safely pass flood flows. Failures caused by hydrologic conditions can range from sudden failure, with complete breaching or collapse of the dam, to gradual failure, with progressive erosion and partial breaching”.[2] Therefore, hydrologic studies are among the most important sources of information when it comes to dam safety.
Hydrologic Design Criteria
“Selection of an Inflow Design Flood (IDF) for a new dam or a dam undergoing significant modifications should taken into account both current conditions and reasonably anticipated future development. Development within the upstream watershed can cause increased runoff and peak flows, while development within the downstream inundation area can alter hazard potential classification and specific estimates of consequences of hydrologic events… When the cost of more detailed methods such as incremental consequence analysis, a site-specific probable maximum precipitation study, or risk-informed hydrologic hazard analysis is prohibitive, prescriptive IDF criteria for High, Significant, and Low Hazard dams are recommended”.[2]
The applicability and acceptability of various hydrologic methods varies widely across the US. Familiarity with the primary runoff generating mechanisms based on the geology, topography, meteorology, and seasonality of the region are paramount to inflow design flood determination. Guidelines and regulations related to hydrologic methods and the inflow design flow also vary based on regulatory jurisdiction.
Types of Evaluations
- Low Flow Conditions
- Normal Flow Conditions
- Flood Conditions
- Sedimentation
- Groundwater
- Unusual or Changing Conditions in a Watershed
Examples
Best Practices Resources
Technical Release 210-60: Earth Dams and Reservoirs, NRCS, 2019
Selecting and Accommodating Inflow Design Floods for Dams (FEMA P-94), FEMA, 2013
Flood Hydrology Manual, USBR, 1989
Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420), USACE, 1987
Trainings
On-Demand Webinar: Hydrology 101 for Dam Safety
On-Demand Webinar: Hydrology 201 for Dam Safety
Technical Seminar: HEC-HMS with Application to Dam Safety
Citations:
Revision ID: 6667
Revision Date: 03/16/2023