Hydrology


 * =Home Page - Hydrology= || ==//by Austin Heermann//==

//email: heermann@unm.edu//
||

** Introduction **
  Water is a critical resource that humans and animals are dependent upon for survival. Hydrologic resources have a major impact where humans live and work. Sufficient water resources are necessary to grow food, sustain life, and operate many businesses. Due to the hazards that flooding presents to human activities, quantifying flood flows is another important aspect of hydrology. Hydrology is the branch of science focusing on understanding the flow of water in streams, rivers, and groundwater. Hydrology considers low flow (also known as base flow, - low flow will be used through the wikispace) conditions both for quantifying minimum available flow for human use and to assure water flow for habitat protection. Hydrology also quantifies and identifies the risks of flooding to guide the design of flood control systems like dams and levees. For millennia, hydrology was motivated by the need to provide water for human uses. However, a river and stream is more than the water. It is a unique ecosystem that supports bio-diversity.

For thousands of years, rivers and streams were simply viewed as a water supply. With the primary focus toward water, river aspects such as sediment transport or providing habitats for flora and fauna were often overlooked. This oversight has often resulted in ecosystems disruption due to river alterations, such as dams. Ecosystem impacts include effects such as decreased tree growth and decreases in ecosystem populations. Over the past 200 years, dams have become the solution to attenuating the peaks of a natural flow regime to control and store water for human consumption. A shift away from only focusing on reducing flood events and/or supplying water is slowly becoming common practice. During the last decade, scientists and engineers discovered that streams and rivers require flooding, sediment transport, and nutrient resources to maintain equilibrium. River restoration not only requires improvements to the stream but also to non-water resources such as watershed land cover. Land cover has a direct impact on the quality and quantity of the water flowing into the stream.

Hydrology’s primary focus remains on water flow, with an understanding that the flow is a central factor that drives river processes. This wiki discusses hydrologic modeling of river flows and presents flow categories that guide understanding of flow volume on river processes and their effects on river restoration. Hydrologic modeling of the river or stream provides predictions of river flows. The movement of groundwater also plays an important role in tracking water through a system, however this wikispace will focus on surface flows. This wikispace will be to provide an overview of the tools needed to accurately model surface flows. The flow categorization will be discussed to provide the relevance of the flow volume to the stream or river processes.

**Hydrology Modelling Process** At the core of any water model is the proper accounting of the water entering, exiting and stored in a watershed. Accountants use credits and debits to track money flows; in engineering applications, mass balance is used to understand flows in and out of a system. This modelling concept can be used for a hydrologic analysis to quantify the flow of water through the hydrologic cycle also known as the water cycle. A credit of water is supplied through ice and snow runoff and precipitation. Debits of surface water include infiltration, storage, sublimation, evapotranspiration, evaporationand human withdrawals. The remaining water finds its way toward the downhill to the nearest stream.

Studying water flow through a stream is a critical factor that needs to be examined before the initial design begins in a river restoration project. A drainage basin/watershed study can be used to determine the amount of land where surface and subsurface flow will converge at a predetermined point. The water that ends up in a stream comes from several different sources. Similar to a mass balance, water must be tracked as inflows and outflows. Identifying the sources where water enters and exits the system and their locations is the key to understanding the water quantity in the river. Once the location of sources and sinks are identified an accounting method similar to credits and debits should be applied to the water cycle. Examples of these sources might include precipitation, runoff, water storage in the form of ice, snow and reservoir storage. Other sources could include subsurface flow or water from waste water treatment facilities. Later in the wiki, an example is provided on how data sources, modeling techniques and procedures are currently used in the industry.

Natural and human changes to the watershed can impact the water quantity and quality of the stream**.** Examples of physical and chemical changes might include a new housing development, logging operations, or mining. Natural changes that can impact river flow include changes in climate such as the quantity and intensity of precipitation. Humans impact the stream with factors such as the amount of water released from dams. Weather phenomenon, such as La Nina and El Nino, can contribute to dry periods or major flood events. La Nina and El Nino create seasonal temperate shifts that impact the amount of water stored in the atmosphere, which change the precipitation patterns. Since these human and non-human factors can impact the flow regime of a river, various scenarios should be considered in modeling how a change in one or more variables is predicted to change the stream flow. To simulate how changes such as new housing or a mining operation could impact a stream hydrology, water models are constructed to gain a better understanding of the watershed. Numerous commercial and open source computer programs exist to aid in the creation of a hydrologic model. An introduction to the required data and industry standard programs are discussed later in the wiki.

Streams meander through numerous ecosystems, from forested lands to an urban ecosystem. The stream and the land ecosystems interact. Streams provide resources, such as pulse flows, water, and sediment/nutrient transport, that benefit each ecosystem. Each unique ecosystem requires different flow rates. River restoration process requires an understanding of the flow rates. For undeveloped ecosystems, specialties such as environment flows and physical habitat modeling are used to examine the size of flows required. Flooding is often the major hydrologic flow concern for an urban ecosystem.

**Sources of Data for Models** After understanding what influences can impact the quantity of water in a river, a model of the study area should be constructed. The model facilitates understanding how all the factors integrate together and how changes might impact the watershed**. ** Hydrologists and engineers use computer programs to predict how changes in a system will impact the study area. Hydrologic models can help understand relationships that would be impossible to predict without having to modify the existing system. Also, the models are key to understanding the effects of long term changes like climate change.This wikispace will focus on analyzing surface flows. For more information about modeling subsurface flows and ground water models,, see the links provided throughout this wikispace. A beginning step in creating a model and quantifying stream flow includes gathering the needed data for the study. This includes:
 * 1) Precipitation Data - historic data for duration and frequency of storm events
 * 2) Dams and Diversions along the rivers reach
 * 3) Type of Land – undeveloped, parks, concrete and pavement
 * 4) Soil Types
 * 5) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Elevation and Slope Data
 * 6) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Temperature and Climate Data
 * 7) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Type of Vegetation
 * 8) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Water Stream/River Gage Data
 * 9) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Human demand

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Hydrology focuses on the interaction of spatial and temporal variations within a watershed. To understand all of the factors that impact a stream, a minimum of the nine (listed above) different sources of data should be explored. Historic precipitation data will provide information about the quantity and trends in atmospheric water released during a year. Dams and diversions along a river reach can delay the flow of water released during a storm; these delays impact the temporal variations. The type of land cover can impact the amount of runoff that an area experiences. Undeveloped areas will infiltrate more water compared to areas with copious coverage of pavement and concrete. The type of soil influences if and how much water will infiltrate into the ground. Elevation and slopes also impact the amount of runoff, areas with higher grades experience more runoff compared to low grades. Changes in climate relate to temperature and will impact the amount of evaporation and evapotranspiration within a system. Higher temperatures increase the percentage of water that’s released back into the atmosphere. The type of vegetation within the study can impact the amount of evapotranspiration and sediment within a river. The majority of streams have water gauge data tracking the flow and sediment in the river. This data is important for the calibration of the model. If the model closely predicts the historic stream hydrographs and actual water gauge data, the model may accurately predict future conditions. Water withdrawals from cities and municipalities can impact the quantity of water that flows downstream, which can have major implications on the system.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Vegetation water loss is quantified by a term called evapotranspiration, which is the water consumption from the evaporation and transpiration from flora within the watershed. To monitor the water consumed by plants, evapotranspiration (ET) towers are placed along the riparian to measure water losses. ET tower measurement is based on a process called Eddy Covariance; the tower measures the flux or change in water through the rising and descending air currents. This evapotranspiration data is beginning to be utilized in modeling. Issues with obtaining the data is currently a challenge. Software packages, such as the Consortium of Universities for the Advancement of Hydrologic Science, Inc - Hydrologic Information System (CUAHSI-HIS), holds promise to make ET data more readily available.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">To obtain the the necessary data for the the modelling, a list of sources to obtain this information is provided below.

<span style="color: #000000; font-family: arial,helvetica,sans-serif; font-size: 14px;">**Table 1: Recommend Sources of data for water models** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">International Commission on Large Dams || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">New Mexico source:rgis.unm.edu/
 * || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**Agency or Location** || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**Website** ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Precipitation data || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">NOAA’s Nation Weather Service website || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">noaa.gov ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Dams and Diversion || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Site visits, aerial imagery, or possible GIS file locating the type and size of water restriction.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://www.icold-cigb.net/ || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[|www.abcwua.org] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">A common scene approach should be used when selecting data for any hydrologic model. The spatial and temporal variations of data must meet the scope of the model. Sources of hydrologic data include various State and Federal government organizations that maintain data warehouses. Due to national security concerns, certain data may need to be requested via phone or email request. One resource for information includes The University of New Mexico (UNM), which has an extensive database of GIS data for elevation data, high resolution orthophotography, and land cover data. If data does not exist, field surveys will likely be required. <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Type of Land || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">USGS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://landcover.usgs.gov/uslandcover.php ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Soil Types || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">United States Department of Agriculture NRCS (Natural Resources Conservation Service) || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://soildatamart.nrcs.usda.gov/ ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Elevation and Slope Data || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">USGS – National Elevation Dataset (NED) || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://ned.usgs.gov/ ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Temperature and Climate Data || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The National Weather Service || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">weather.gov ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Water Gage Data || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">USGS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://waterdata.usgs.gov/nwis/rt ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Type of Vegetation || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">U.S Department of the Interior || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://www.mrlc.gov/ ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Water Consumption || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">City Government agencies and Local Water Authorities || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[|www.cabq.gov]

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">To help bring all of the data together and understand the spatial relationships for different features, a Geographic Information System (GIS) can be used to define and accurately model the watershed. Listed below are a few common GIS software packages:
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ArcGIS
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">QGIS
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Manifold
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Global Mapper

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Once the data is organized, various flood event scenarios should be created in the model. Within many software packages, various scenarios or lists of different physical possibilities could be created. For example, to simulate a low flow condition, low precipitation data and drought conditions parameters could be studied to understand if certain physical conditions will provide adequate flow for the ecosystem. For modeling flood flows, a high intensity storm event could be combined with high annual precipitation data to predict flood conditions. Worst case scenarios, such as increased paved areas with higher runoff, should also be considered as an additional scenario.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Hydrologic Models** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Below is a list of popular hydrologic modeling software. This wikispace will not cover the aspects of creating a model. A majority of the links provided include user guides/tutorials that walk modelers step by step through the processes and workflows of model creation. Prior preparation of data (see above: sources of data for models) is needed before constructing a model. Programs, such as USACE HEC-GeoHMS, facilitate the organization of the GIS data while also building the framework for the hydrologic model.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Table 2: Programs Used for Hydrologic Analyses**

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">http://www.gsshawiki.com/gssha/Main_Page || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">US Army Corps of Engineers || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 5.7 (January 2011) ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Name of Program** || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Cost** || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Web Address** || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Company** || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Latest Release** ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">WEAP || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">0-3000 USD || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://www.weap21.org/ || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Stockholm Environment Institute || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 3.22 ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">HEC – HMS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Free || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">@http://www.hec.usace.army.mil/software/hec-hms/ || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">US Army Corps of Engineers || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 3.5 ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">HEC-Geo-HMS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Free || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">US Army Corps of Engineers || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 5 –ArcGIS 9.3Version 10 – ArcGIS 10 ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">PRMS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Free || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">USGS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Numerous Software Packages Available ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">GSSHA || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Free || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[]
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Arc – Hydro || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">TBA || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ESRI - Environmental Systems Research Institute || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 10 ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ArcGIS – need for HEC-GeoHMS || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">100 – 25,000 USD || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ESRI - Environmental Systems Research Institute || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Version 10 ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">CUAHSI - Hydrologic Information System (HIS) || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Free || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[] || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Consortium of Universities for the Advancement of Hydrologic Science, Inc. and the National Science Foundation || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Updated Regularly ||

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Types of Hydrologic Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Three categories of flows should be examined during any restoration projection. The categories include; low flows, channel forming flows, and flood flows. Within the channel forming category, three subcategories exist; bank full discharge, dominant discharge, and effective discharge. Examples and a discussion of these five types of flows are explained below. A table overview of each type flow is included in the table below.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Table 3: Overview of types of flows, with definitions and limitations** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">- Neglects broader needs of environmental flows || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">over a period of years || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">See example later in <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">wikispace || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">- Doesn't specifically address causes for non-equilibrium conditions || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">- Significant only in stable alluvial channels || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> Xd,T = the logarithm of the annual minimum d-day low flow for which the flow is not exceeded in 1 of T years or which has a probability of p = 1/T of not being exceeded in any given year <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> Md = the mean of the logarithms of annual minimum d-day low flows <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> Sd = the standard deviation of the logarithms of the annual minimum d-day low flows <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> KT = the Pearson Type III frequency factor
 * || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**Type of Flow** || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**Definition** || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**How to Calculate** || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">**Limitations** ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Low Flow || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Low || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Enough to provide for ecosystem || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Xd,T = Md – KTSd || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> - No set standard
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Effective Discharge || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Channel Forming || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Transports the largest fraction of the sediment load
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Bankfull || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Channel Forming || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Fills the alluvial channel to the floodplain || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Channel Geometry || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">-Function of the data, not the same through out the stream
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Dominant Discharge || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Channel Forming ||  ||   || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">- Concept evolved in irrigation channels ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Flood Floods || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Flooding || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">When water is flowing over the edge of the river onto the flood plain ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">- Focus on flood flows can overshadow other important aspects of hydrology ||

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Low flow conditions provide just enough flow for habitats and ecosystems. A river's flow could potentially get so low that insufficient water is available to support all species in an ecosystem. Studies are completed to determine how much flow is required to support species in the stream ecosystem, see environmental flows for more information. Similar to a hydrologic model, physical habitat models provide simulations of the biological life cycle. A habitat model can answer questions such as what is the minimum flow required for a species to survive. The minimum flow should be analyzed for both depth and velocity. Certain flow conditions are critical to fish vitality and proper hydraulics conditions for fish spawning. Teaming with biologists to help determine the ecosystem flow requirements should be part of the analysis. See environment flows and physical habitat modeling for more information on determining the flow rates for an ecosystem.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Channel Forming Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Once the low flow condition is determined, another river flow that should be analyzed is the channel forming flow. Channel forming flow is important because it can change the river morphology. Three categories of channel forming flows should be considered; bankfull discharge, dominant discharge, and effective discharge. A short relationship to help understand these three flow conditions can be stated simply by:

<span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">Bankfull Discharge = Field Measurement <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">Dominant Discharge = Theoretical <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">Effective Discharge = Computational <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Bankfull Discharge** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Bankfull Discharge is the maximum amount of water that a stable alluvial channel can have before overflow onto the bank would occur. Think of Bankfull Discharges as the maximum water that the river can hold. The bankfull discharge is the boundary condition between a river and a floodplain. Link: [] <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The USDA forest service created three videos showing how to determine the bankfull discharge for the Northeast, Western, and Eastern rivers. See Link: @http://www.stream.fs.fed.us/publications/videos.html

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Dominant Discharge** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">According to the United States Army Crops of Engineers (USACE), Dominant Discharge is defined " as a theoretical discharge that if maintained indefinitely would produce the same channel geometry as the natural long-term hydrograph." (ERDC/CHL CHETN-VIII-5, 2000) In reality, this value is constantly changing due to the dynamic changes of channel geometry. The dominant discharge also assumes that neither aggradation or degradation occur. This concept was developed for the design of stable irrigation canals.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Effective Discharge** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Effective Discharge is important for river restoration; it estimates the largest fraction of the bed-material load based on different flows. To calculate effective discharge, three steps will need to be performed. First, the flow frequency distribution plot can be obtained from USGS gage data. Next, a bed material-load rating curve should be constructed to quantify the type of sediment in the river. This can be accomplished using gage data from the USGS or field tests. Lastly, the discharge flow and sediment discharge curve are plotted on the same graph. Another curve should be plotted, which is the product of the flow discharge and sediment discharge. The peak of this curve produces the effective discharge. The United States Army Corp. of Engineers recommends comparing this theoretical value vs. actual data due to the unique characteristics of each stream. For more information about effective discharge, the United States Army Corp. of Engineers published a technical note to provide the methods and equations used while calculating effective discharge.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Below is an example of how to calculate the effective discharge. The Microsoft (MS) Excel files can be downloaded to examine the details of the analysis.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Data can be download from USGS website at: @http://water.usgs.gov/

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Request a stage-discharge rating curve from the USGS. Below is an MS Excel file with a stage-discharge rating curve for the Rio Grande.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The figures below illustrate the process for determining the Effective Discharge. <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Note: Effective Discharge = Downloaded Gauge Data* Sediment Discharge Curve


 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[[image:step1.PNG width="389" height="295"]] || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 80px; text-align: center;">* || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[[image:step2.PNG width="392" height="296"]] || <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 80px; text-align: center;">= || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[[image:step3.PNG width="410" height="286"]] ||

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The MS Excel file that was used to preform this Effective Discharge analysis can be downloaded here: <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">

A pdf documents from the showing the equations used for the Discharge_Example.xlsx spreadsheet. The original Chapter 3 document from US Bureau of Reclamations - Erosion and Sedimentation Manual - November 2006 <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Flood Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Flood flows are important from a human safety standpoint. The focus of the analysis is to determine how far the water would rise and what homes and businesses could be impacted by a flood. This calculated boundary is useful for home owners and home insurance companies to understand some of the risks of living on a flood plain. The Federal Emergency Management Agency (FEMA) publishes flood maps showing the locations that would be effected during a 100-year and 500-year flood events. For more information about how to calculate the probabilities of a 100 year or 500 year storm event, refer to the probability section located at the bottom of this wiki. Zones have been created based on different flood events. An explanation of the zones is presented in Table 4. Acronyms used in Table 4 are defined below the table.

<span style="color: #800080; font-family: arial,helvetica,sans-serif; font-size: 14px;">** Table 4 : FEMA Flood Zone Categories **
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">High Risk Areas ||  |||| <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">Moderate to Low Risk Areas ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">In communities that participate in the NFIP, mandatory flood insurance purchase requirements apply to all of these zones: ||  |||| <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">In communities that participate in the NFIP, flood insurance is available to all property owners and renters in these zones: ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ZONE || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">DESCRIPTION ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ZONE || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">DESCRIPTION ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">A || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Areas with a 1% annual chance of flooding and a 26% chance of flooding over the life of a 30-year mortgage. Because detailed analyses are not performed for such areas; no depths or base flood elevations are shown within these zones. ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">B and X (shaded) || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floods. Are also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100-year flood, or shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile. ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">AE || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The base floodplain where base flood elevations are provided. AE Zones are now used on new format FIRMs instead of A1-A30 Zones. ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">C and X (unshaded) || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Area of minimal flood hazard, usually depicted on FIRMs as above the 500-year flood level ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">A1-30 || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">These are known as numbered A Zones (e.g., A7 or A14). This is the base floodplain where the FIRM shows a BFE (old format). ||  ||   ||   ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">AH || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Areas with a 1% annual chance of shallow flooding, usually in the form of a pond, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30-year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones. ||  ||   ||   ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">AO || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">River or stream flood hazard areas, and areas with a 1% or greater chance of shallow flooding each year, usually in the form of sheet flow, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30-year mortgage. Average flood depths derived from detailed analyses are shown within these zones. ||  ||   ||   ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">AR || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Areas with a temporarily increased flood risk due to the building or restoration of a flood control system (such as a levee or a dam). Mandatory flood insurance purchase requirements will apply, but rates will not exceed the rates for unnumbered A zones if the structure is built or restored in compliance with Zone AR floodplain management regulations. ||  ||   ||   ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">A99 || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Areas with a 1% annual chance of flooding that will be protected by a Federal flood control system where construction has reached specified legal requirements. No depths or base flood elevations are shown within these zones. ||  ||   ||   ||

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">NFIP: National Flood Insurance Program <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">FIRM: Flood Insurance Rate Map <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">BFE: Base Flood Elevation
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">High Risk - Coastal Areas ||  ||   ||   ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">In communities that participate in the NFIP, mandatory flood insurance purchase requirements apply to all of these zones: ||  |||| <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: center;">Undetermined Risk Areas ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ZONE || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">DESCRIPTION ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">ZONE || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">DESCRIPTION ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">V || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. These areas have a 26% chance of flooding over the life of a 30-year mortgage. No base flood elevations are shown within these zones. ||  || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">D || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Areas with possible but undetermined flood hazards. No flood hazard analysis has been conducted. Flood insurance rates are commensurate with the uncertainty of the flood risk. ||
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">VE, V1 - 30 || <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. These areas have a 26% chance of flooding over the life of a 30-year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones. ||  ||   ||   ||

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Link for documentation about FEMA Zones, published by FEMA.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Other Types of Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">In addition to low flows, channel forming flows, and flood flows other flow conditions should be analyzed to understand the system. Examples of other flows are seasonal flows or future flows.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Seasonal Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Throughout the year, certain seasonal conditions cause flows to exceed the normal runoff peak. In the Mountain West, the normal peak flow results from the Spring snowpack melt. The water storage in the snowpack should be included in any hydrology model that includes snow within the study area. A New Mexico example of increased runoff occurs during the monsoon season. During this period, New Mexico receives the majority of its annual precipitation. The monsoon rains are often high intensity storms that generate short narrow spikes in the hydrograph. The City of Albuquerque publishes rainfall intensity values. Most New Mexico counties publish min, avg ,and max values for rainfall intensity. These rainfall intensity values are important for the USACE HEC hydrologic models, which can greatly impact the final results of a model.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Future Flows** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;"> Although much of the recommended data mentioned above includes historic data for modeling, future flows should also be included. Droughts or human management practices can change the future flows and should be implemented in the hydrologic model. E xamples of future flows include, re-routing of water from one basin to another, the construction/decommissioning of a dam along the stream reach, or climate change. Changes to future flows can result from residential and commercial development, changes in water rights and how water could be stored or consumed. Future flows can be significantly different than historical hydrographs, so it important that future flows be considered.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Probability and Distribution
<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Probability and distribution play an important role in understanding the frequency of a flood event. Statistics are an important tool in determining the frequency of a flood pulse, which is another important element of river restoration.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Equation for Probability: P = 1/(Recurrence interval or return period).

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">For example, a 100 year flow states that chance of the event occurring is 0.01 or 1 percent. A major public misconception is that a 100 year event will only happen once every one hundred years, the Mississippi river has exceeded the 100 year storm event more than once in the past 100 years. According to the NOAA website, over 21 flooding events have occurred during the past 100 years.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">To understand how a 100 year event could occur more than once every 100 years, a distribution of events should be used. Four types of probability distribution functions are used:
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Normal Distribution
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Log- Normal Distribution
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Log- Pearson Type III Distribution
 * <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Gumbel Distribution

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">The selection of a probability distribution is application dependent.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**Conclusion**

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Historically, the primary hydrologic concern was creating a reliable source of water for human uses. Recently, a push to understand how humans and ecosystems can thrive and flourish together has motivated a wider use of hydrologic analysis to support river restoration activities. River restoration depends on understanding the behavior of the river as system of interacting elements. Hydrology plays an important role in river restoration and is crucial to understanding the river as a system before any restoration project begins. Since the flow rate governs most river processes, the main purpose of hydrology is tracking water flow through the temporal and spatially variations within the watershed. Hydrologic tools enable engineers and hydrologist to determine the extreme flows such as low flow to flooding conditions. Various modeling packages simulate the physical interaction between precipitation, runoff, ground water, reservoir storage, river flows, and land cover. Good data are the foundation of any hydrologic model and data are often available from local, regional and federal government agencies. The models predict the impacts of human activities and natural variations, such as changes in land cover, annual precipitation, and climate. The model predictions provide important insight into river ecosystem vitality and enable sustainable river management today and in the future.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">**References:** <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Chanson, Hubert. 1999 The Hydraulics of Open Channel Flow An Introduction. John Wiley & Sons Inc.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Wurbs. R.A. James, 2002 W.P. Water Resources Engineering Prentice Hall.

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">//Fischenich, J.C. McKay, SK.// 2011 Hydrologic Analyses for Stream Restoration Design ERDC TN-EMRRP-EBA-8. March 2011

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">USDA. - Natural Resources Conservation Service (2001) Stream Corridor Restoration Principle, Processes, and Practices. The Federal Interagency Stream Restoration Working Group. <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[|NEH-653: Federal Stream Corridor Restoration Handbook]

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">United State of Department of Agriculture. Natural Resources Conservation Service. (2007) Part 654 National Engineering Handbook. Stream Hydrology. Chapter 5. August 2007 <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">[|NEH-654: Stream Restoration Design] <span style="font-family: arial,helvetica,sans-serif; font-size: 14px; line-height: 0px; overflow: hidden;">

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Copeland, R. R. et. al (2000) Channel Forming Discharge. ERDC/CHL CHETN-VIII-5 United States Army Corps of Engineers (December 2000) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Biedenharn, D.S. et al. (2000). Effective Discharge Calculations. ERDC/CHL CHETN-VIII-4 United States Army Corps of Engineers (December 2000) <span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">

<span style="font-family: arial,helvetica,sans-serif; font-size: 14px;">Fleming M.J., Doan H.H. 2009 HEC- GeoHMS Geospatial Hydrologic modeling Extension User Guide 4.2 US Army Corps of Engineers, Institute for Water Resoues Hydrogloic Engineering Center (HEC) Link