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(Created page with "__NOTOC__ ---- <!-- Delete any sections that are not necessary to your topic. Add pictures/sections as needed --> [Paragraph here] ==Required Data== *''Watershed Delineation'' ::“For most hydrologic studies, it is essential that good topographic maps be used. It is important that the maps contain contours of ground-surface elevation, so that drainage basins can be delineated and important features such as slopes, exposure, and stream patterns can be measured”.<ref...")
 
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[[Category:Flood Hydrology]]
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"Rainfall-runoff modeling can be used to simulate the processes involved with converting rainfall and/or [[snowmelt]] into a hydrograph representing the upper level or maximum flood runoff that a drainage basin might reasonably be expected to produce. The unit hydrograph approach is the basic tool or “model” to convert rainfall to runoff after abstracting suitable infiltration losses. However, it should be noted that there are a number of other techniques available for making this conversion, including highly complex computerized watershed models."<ref name="Reclamation">[[Flood Hydrology Manual| Flood Hydrology Manual (United States Bureau of Reclamation, 1989)]]</ref>
 
"In 1932, Leroy K. Sherman initially proposed the unit hydrograph approach to convert rainfall occurring over a drainage basin to flood runoff from that basin. Sherman’s approach, which was formally presented in the April 7, 1932, issue of [[Engineering]] News Record, has undergone considerable refinement over the years. The advent of high speed electronic computers has led a number of hydrologists to devise approaches using complex watershed models, as alternatives to the unit hydrograph model, to predict a drainage basin’s runoff response to rainfall. Many of these watershed models are an appropriate basis for simulating a continuous series of runoff responses to normal [[precipitation]] events. However, in the Bureau of Reclamation’s application, the primary interest is in simulating a basin’s runoff response to extreme rainfall events. Because these complex watershed models generally require extensive calibration to adequately represent a drainage basin’s physical properties, considerable-effort must be expended in the field and office in acquisition of data relative to these properties. In the final analysis, the relative “goodness” of an approach is measured by how well that approach reproduces actual recorded flood events. Comparative studies have indicated that both approaches are able to satisfactorily reproduce these events with neither one being notably superior to the other. Accordingly, the Bureau has, over the years, retained the unit hydrograph approach because of its simplicity, reliability, and the relatively low costs associated with its application to flood [[hydrology]] studies."<ref name="Reclamation"/>


==Required Data==
==Required Data==
*''Watershed Delineation''
* [[Watershed Delineation]]
* [[Precipitation Depth]]
* [[Precipitation Temporal Distribution]]
* [[Precipitation Spatial Distribution]]
* [[Rainfall Losses]]
* [[Unit Hydrograph]]
* [[Reach Routing]]


::“For most hydrologic studies, it is essential that good topographic maps be used. It is important that the maps contain contours of ground-surface elevation, so that drainage basins can be delineated and important features such as slopes, exposure, and stream patterns can be measured”.<ref name="EM 1110-2-1420">[[Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420) | EM 1110-2-1420 Hydrologic Engineering Requirements for Reservoirs, USACE, 1997]]</ref>
==Best Practices Resources==
 
{{Document Icon}} [[National Engineering Handbook: Chapter 4 - Storm Rainfall Depth and Distribution | National Engineering Handbook: Chapter 4 - Storm Rainfall Depth and Distribution, NRCS]]
*''Precipitation''
{{Document Icon}} [[Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 8- Determination of the Probable Maximum Flood | Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 8- Determination of the Probable Maximum Flood, FERC]]
 
{{Document Icon}} [[Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420) | Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420), USACE]]
::“In areas of relatively uniform terrain and little spatial variability or precipitation, classical textbook procedures, such as Thiessen polygons or the isohyetal method, can be used and are generally adequate. These procedures are simple methods of developing spatial averages from point measurements but are inadequate to describe the orthographic or other spatially variable behavior of any appreciable complexity. In these cases, such as in mountainous areas, more comprehensive algorithms are needed to develop spatial averages from point measurements that describe the elevational (vertical) and horizontal variability. For time series at the watershed scale, the algorithm based on detrended kriging developed by Garen, Johnson, and Hanson (1994) is an example. (Further information on this procedure is available from the NRCS National Water and Climate Center in Portland, Oregon.) For annual or monthly averages or monthly time series at somewhat larger spatial scales (watershed to regional), the best method is to use the PRISM maps and GIS layers, as mentioned previously. This would be the recommended procedure in most watershed yield analyses”.<ref name="NEH210-630-20">[[National Engineering Handbook 210 Part 630 Hydrology: Chapter 20 Watershed Yield | National Engineering Handbook 210 Part 630 Hydrology: Chapter 20 Watershed Yield, NRCS, 2009]]</ref>
{{Document Icon}} [[Flood Hydrology Manual | Flood Hydrology Manual, USBR]]
 
*''Rainfall Losses''
 
*''Unit Hydrograph''
 
*''Reach Routing''


==Examples==
{{Website Icon}}
==Best Practices Resources==
{{Document Icon}} [[Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420)]]
{{Document Icon}} [[National Engineering Handbook 210 Part 630 Hydrology: Chapter 20 Watershed Yield]]
==Trainings==
==Trainings==
{{Video Icon}}
{{Video Icon}} [[On-Demand Webinar: Introduction to Hydrologic Modeling Using Geospatial Information]]


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Latest revision as of 04:38, 21 July 2023


"Rainfall-runoff modeling can be used to simulate the processes involved with converting rainfall and/or snowmelt into a hydrograph representing the upper level or maximum flood runoff that a drainage basin might reasonably be expected to produce. The unit hydrograph approach is the basic tool or “model” to convert rainfall to runoff after abstracting suitable infiltration losses. However, it should be noted that there are a number of other techniques available for making this conversion, including highly complex computerized watershed models."[1]

"In 1932, Leroy K. Sherman initially proposed the unit hydrograph approach to convert rainfall occurring over a drainage basin to flood runoff from that basin. Sherman’s approach, which was formally presented in the April 7, 1932, issue of Engineering News Record, has undergone considerable refinement over the years. The advent of high speed electronic computers has led a number of hydrologists to devise approaches using complex watershed models, as alternatives to the unit hydrograph model, to predict a drainage basin’s runoff response to rainfall. Many of these watershed models are an appropriate basis for simulating a continuous series of runoff responses to normal precipitation events. However, in the Bureau of Reclamation’s application, the primary interest is in simulating a basin’s runoff response to extreme rainfall events. Because these complex watershed models generally require extensive calibration to adequately represent a drainage basin’s physical properties, considerable-effort must be expended in the field and office in acquisition of data relative to these properties. In the final analysis, the relative “goodness” of an approach is measured by how well that approach reproduces actual recorded flood events. Comparative studies have indicated that both approaches are able to satisfactorily reproduce these events with neither one being notably superior to the other. Accordingly, the Bureau has, over the years, retained the unit hydrograph approach because of its simplicity, reliability, and the relatively low costs associated with its application to flood hydrology studies."[1]

Required Data

Best Practices Resources

National Engineering Handbook: Chapter 4 - Storm Rainfall Depth and Distribution, NRCS

Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 8- Determination of the Probable Maximum Flood, FERC

Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420), USACE

Flood Hydrology Manual, USBR

Trainings

On-Demand Webinar: Introduction to Hydrologic Modeling Using Geospatial Information


Citations:


Revision ID: 7351
Revision Date: 07/21/2023