Description:
The Runoff Processes module offers a thorough introduction to the runoff processes critical for flood and water supply prediction. Through the use of rich illustrations, animations, and interactions, this module explains key terminology and concepts including paths to runoff, basin and soil properties and runoff modeling. It also provides an introduction to the National Weather Service River Forecast System (NWSRFS). As a foundation topic for the Basic Hydrologic Science course, this module may be taken on its own or used as a supporting topic to provide factual scientific information to students as they complete the case-based forecasting modules.

Objectives:
Explain basic runoff processes:
* Define rainfall runoff
* Identify the general movement of water both on the surface and in the ground
* Recognize the different terms associated with groundwater and runoff
* Understand the relationship between precipitation/snowmelt rate and infiltration

Describe the paths for runoff:
* Identify the different types of runoff that occur both at and below the surface
* Recognize the influence of surface and soil properties that influence surface runoff
* Understand the soil properties that influence subsurface runoff, or interflow
* Anticipate the types of runoff you may expect in your area given the rainfall/snowmelt rate and the soil properties

Explain basic basin issues related to runoff:
* Recognize basin characteristics and how the relate to runoff processes
* Explain the impact of urbanization on runoff characteristics

Describe how soil properties affect runoff:
* Anticipate water movement and runoff given soil characteristics
* Identify important soil properties in your area
* Understand how both natural and human factors influence the behavior of water in the soil

Describe basic concepts of runoff modeling:
* Understand the basic concepts in runoff modeling
* Recognize why complex versus simple models are used
* Describe how a lumped model works
* Describe how a semi-distributed model works
* Describe how a distributed model works and the potential advantages as well as limitations

Describe features of basic National Weather Service River Forecast System (NWRFS) models:
* The key components and subcomponents of the NWRFS
* Basic concepts behind and components of the SACSMA model
* Basic concepts behind and components of the API and Continuous API models

Estimated time to complete: 2-2.5 h

Description:
The role of unit hydrograph theory in the flood prediction process is to provide an estimate of streamflow given the precipitation. A unit hydrograph shows the temporal change in flow, or discharge, per unit of runoff from excess precipitation. In other words, the unit hydrograph shows how the flow of a stream will be affected over time by the addition of one unit of runoff. This module offers a thorough introduction to the use of unit hydrographs and the application of unit hydrograph theory in flood prediction. Through use of rich illustrations, animations, and interactions, this module explains key terminology and assumptions, outlines the steps in creation of a unit hydrograph, examines the issues surrounding application of unit hydrograph theory, and discusses important considerations for forecasters.

Objectives:
1. Define key features of unit hydrographs and of unit hydrograph theory.
• Explain why we need unit hydrographs.
• Describe how unit hydrograph theory is used as a tool in forecasting runoff.
• Define the basic components of a unit hydrograph.

2. Identify important terms and assumptions in unit hydrograph theory.
3. Explain key issues for application of unit hydrograph theory.
• Identify reasons that some precipitation events may not be accurately represented by a unit hydrograph.
• Explain the impact of using English or metric units of measure.
• Describe the process for application of unit hydrographs to storms covering multiple time durations.
4. Recognize the forecast implications of unit hydrograph theory for real precipitation events.
• Describe potential effects on actual hydrograph data based on storm coverage and basin changes.

Estimated time to complete: 1.5-2 h

Description:
This module offers a thorough introduction to streamflow routing methods and applications in the river forecasting process. Through the use of rich illustrations, animations, and interactions, this module explains key routing concepts, flow characteristics, and tools with a primary focus on hydrologic routing methods. As a foundation topic for the Basic Hydrologic Science Course, this module may be taken on its own or used as a supporting topic to provide factual scientific information to students as they complete the case-based forecasting modules.

Objectives:
1. Demonstrate an understanding of the streamflow routing process

2. Define streamflow routing:
a. Interpret stage and discharge graphs
b. Describe applications of streamflow routing
c. Explain how streamflow routing fits into the flood prediction process
d. Describe the major approaches used in streamflow routing

3. Describe the storage-release concept and the accounting budget approach

4. Describe flow categories and impact on the choice of routing method

5. Define common terms used to describe physical characteristics of streams

6. List the factors used in determining streamflow velocity and discharge via Manning’s equation

7. Use rating curves to determine the stage-discharge relationship, i.e., the expected discharge for a given depth of water at a given point for a given period

8. Explain concepts used in streamflow routing:
a. Describe how routing process is applied in river forecasting
b. Explain how storage concept is applied in routing
c. Describe wedge and prism storage approach as applied in the Muskingum method

9. Apply the Lag and K method for streamflow routing

10. Identify how hydraulic routing methods differ from hydrologic methods:
a. Describe when one might choose to use hydraulic over hydrologic methods

Estimated time to complete: 1.5-2 h

Description:
According to NOAA’s National Weather Service, a flash flood is a life-threatening flood that begins within 6 hours--and often within 3 hours--of a causative event. That causative event can be intense rainfall, the failure of a dam, levee, or other structure that is impounding water, or the sudden rise of water level associated with river ice jams.
The “Flash Flood Processes” module offers an introduction to the distinguishing features of flash floods, the underlying hydrologic influences and the use of flash flood guidance (FFG) products. Through use of rich illustrations, animations, and interactions, this module explains the differences between flash floods and general floods and examines the hydrologic processes that impact flash flooding risk. In addition, it provides an introduction to the use of flash flood guidance (FFG) products including derivation from ThreshR and rainfall-runoff curves as well as current strengths and limitations.

Objectives:
Define a flash flood:
• Distinguish a flash flood from a general flood
• Identify the different physical processes leading to flash floods
• Recognize the connection between precipitation intensity and runoff characteristics associated with flash floods

Explain hydrologic influences on flash floods:
• Apply information about the runoff processes to the flash flood problem
• Explain why certain soil textures and soil profiles may result in greater flash flood risks
• Which physical characteristics make a basin more prone to flash flooding
• How quickly and frequently flash floods can occur in urban environments
• How fires and deforestation impact the flash flood risk

Understand key issues underlying the use of flash flood guidance (FFG) products:
• The definition of flash flood guidance
• How threshold runoff (ThreshR) and rainfall-runoff curves are used to derive flash flood guidance
• How flash flood guidance is generated for different spatial entities (headwater, county, gridded) and time durations
• Recognize when and how limitations can impact forecasts

Estimated time to complete: 1 h

Description:
The Flood Frequency Analysis module offers an introduction to the use of flood frequency analysis for flood prediction and planning. Through use of rich illustrations, animations, and interactions, this module explains the basic concepts, underlying issues, and methods for analyzing flood data. Common concepts such as the 100-year flood and return periods as well as issues affecting the statistical representation of floods are discussed. Common flood data analysis methods as well as an overview of design events are also covered. As a foundation topic for the Basic Hydrologic Science course, this module may be taken on its own, but it will also be available as a supporting topic providing factual scientific information to support students in completion of the case-based forecasting modules.

Objectives:

1. Explain key concepts in flood frequency analysis
• Define the meaning of return periods (i.e., the 100-year flood)
• Explain the exceedance probability and its relationship to return period
• Understand the two primary applications of flood frequency analyses


2. Understand key issues impacting the statistical representation of floods
• Explain how the period of record impacts flood frequency guidance
• Calculate the probability of occurrence or non-occurrence for a given flood magnitude over a specified duration
• Understand how basin changes may impact the behavior and frequency of floods, thus reducing the length of the period of record


3. Apply common methods for analyzing flood data
• Explain the basic concepts underlying both annual and partial duration time series
• Conduct a frequency analysis given peak flow data for a river


4. Explain purpose and application of design events
• Identify the reason for using design events
• Understand the usefulness of design events and their limitations and constraints
• Explain the concept of probable maximum event
• Understand the concept of standard project floods

Estimated time to complete: 1-2 h

Description:
This module takes the learner through the considerations for the river forecasting decisions associated with the remnants of Hurricane Ivan on 17-19 September, 2004 for the Susquehanna River system in Pennsylvania and New York. The module assists the learner with applying the concepts covered in the foundation topics of the Basic Hydrologic Sciences course. Some of the specific topics pertinent to this case are soil conditions, the impact of QPF on runoff, runoff models, runoff processes, routed flow and stage-discharge relationships. Observations of upstream conditions and comparisons to historic crests are also examined to assist with operational flood forecast decisions. The core foundation topics are recommended as a prerequisite since this module assumes some pre-existing knowledge of hydrologic principles.

Objectives:
1. Describe hydrologic conditions in the Susquehanna River basin preceding the events associated with the remnants of Hurricane Ivan in the Susquehanna River Basin on the 17-19 September 2004.

a. Describe the local geography and its impact on storm runoff
b. Use climatology as a reference for potential storm impacts
c. Describe soil texture, soil profile, and ground cover conditions for the region
d. Analyze antecedent soil moisture levels for the area

2. Analyze the observed and forecast rainfall, current factors influencing runoff, and the initial river forecasts for the Susquehanna River preceding this event.

a. Analyze rainfall and soil information and anticipate the impact on runoff
b. Interpret runoff information from river models
c. Anticipate how errors in the QPF may impact the magnitude of runoff

3. Apply knowledge of runoff processes and river modeling to observed and historic streamflows to develop a forecast for the Susquehanna River at Wilkes-Barre for this event.

a. Analyze and anticipate dominant runoff mechanisms during a developing flood event
b. Examine the relative contributions from different components of the forecast hydrograph
c. Examine how changes in precipitation can influence the expected crest
d. Analyze how precipitation forecast errors impact runoff forecast errors
e. Anticipate the impact of runoff that is routed from upstream areas
f. Use observations and historic information to assess the likelihood of the predicted extreme event
g. Interpret and adjust guidance from river forecasting models
h. Issue a river forecast despite uncertainties
i. Appreciate how forecaster experience can play a very important role in the forecast process.

4. Assess lessons learned during the forecast process leading up to and during this flood event.

a. Validate how the river forecast model did for the peak stage
b. Interpret how the different components of the river model contributed to the forecast and its errors
c. Explain the important role of accurate stage-discharge relationships
d. Relate this event to previous major flood events

Estimated time to complete: 120 min

Description:
This module takes the learner through seven case studies of flash flood events that occurred in the conterminous U.S. between 2003 and 2006. The cases covered include:

* 30-31 August 2003: Chase & Lyon Counties, KS
* 16-17 September 2004: Macon County, NC
* 31 July 2006: Santa Catalina Mountains near Tucson, AZ
* 25 December 2003: Fire burn area near San Bernardino, CA
* 30 August 2004: Urban flash flood in Richmond, VA
* 19-20 August 2003: Urban flash flood in Las Vegas, NV
* 9 October 2005: Cheshire County, NH

This module assists the learner in applying the concepts covered in the foundation topics of the Basic Hydrologic Sciences course. Some of the specific topics pertinent to these cases are the physical characteristics that make a basin prone to flash floods, basin response to precipitation, flash flood guidance (FFG), the relationship between wildfire and flash floods, and the relationship between urban development and flash floods. Related topics brought out in the cases include radar quantitative precipitation estimation (QPE), the National Weather Service Flash Flood Monitoring and Prediction (NWS FFMP) products, debris flows, impounded water, and interagency communications. The core foundation topics are recommended prerequisite materials since this module assumes some pre-existing knowledge of hydrologic principles. In particular, the Runoff Processes and Flash Flood Processes modules contain material directly related to these cases.

Objectives:
1. Understand the hydrologic response to intense rainfall that leads to rapid runoff and flash floods.

2. Recognize the utility and limitations in NWS flash flood forecasting tools (FFMP, FFG, Radar QPE).

3. Understand that flash flood prone basins can be very small.

4. Identify the LEC (Low Echo Centroid) storm signature and realize its implications on rainfall production.

5. Understand the utility and limitations of different Z-R relationships.

6. Recognize the information provided by FFMP's (Flash Flood Monitoring and Prediction) upstream/downstream tool.

7. Recall how and why FFMP basin rainfall can mask radar problems such as terrain blocking.

8. Think about how one may use other data in areas with terrain blocking of the radar beam.

9. Understand the impact that fire may have on basin hydrology.

10. Recall how debris flows can occur with flash floods.

11. Understand how changing the FFG values may be appropriate in some situations.

12. Recognize the important information provided by FFMP's difference and ratio fields.

13. Be aware of important collaborative efforts between the NWS and other agencies, such as the USGS.

14. Understand the dramatic impact that urban and suburban development can have on basin response.

15. Understand how and why FFG may need to be altered in urbanized areas.

16. Anticipate the very short time lag between peak rainfall and peak flooding in urbanized areas.

17. Recognize that flash flooding may occur downstream of basins that receive the greatest rainfall.

18. Recognize the potential of flash flooding from the sudden release of water impounded by human engineered structures.

19. Recognize the importance of interagency communication prior to and during flash flood events, especially those that involve structural failures.

Estimated time to complete: 1 h