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GLOSSARYDistributed Hydrologic Modeling and GIS Terms
ALBERS EQUAL AREA PROJECTION
The Albers Equal Area projection is a method of projection on which the areas of all regions are shown in the same proportion of their true areas. The meridians are equally spaced straight lines converging at a common point, which is normally beyond the pole. The angles between them are less than the true angles. The parallels are unequally spaced concentric circular arcs centered on the point of convergence of the meridians. The meridians are radii of the circular arcs. The poles are normally circular arcs enclosing the same angle as that enclosed by the other parallels of latitude for a given range of longitude.
Albers Equal Area is frequently used in the ellipsoidal form for maps of the United States in the National Atlas of the United States, for thematic maps, and for world atlases. It is also used and recommended for equal-area maps of regions that are predominantly east-west in extent.
ARC SECOND
1/3600th of a degree (1 second) of latitude or longitude. The length of arc subtended is approximately 30 meters.
ARC/INFO
ARC/INFO is a geographic information system (GIS) used to automate, manipulate, analyze, and display geographic data in digital form. ARC/INFO is a proprietary system developed and distributed by the Environmental Systems Research Institute, Inc., in Redlands, California.
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DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement.
ARCVIEW
ArcView and ArcGIS are desktop geographic information systems (GIS) used to automate, manipulate, analyze, and display geographic data in digital form. ArcView is a proprietary system developed and distributed by the Environmental Systems Research Institute, Inc., in Redlands, California.
DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement.
ASCII—American Standard Code for Information Interchange
A seven-bit code standard adopted to facilitate data interchange between computers and operating systems. These codes represent alphanumerics and special characters (for example, $, /, ?, !).
AWIPS
Acronym for Advanced Weather Interactive Processing System; a computerized system that processes data received at a NWS Forecast Office from various weather observing systems.
BACKFLOW
The backing up of water through a conduit or channel in the direction opposite to normal flow. Also referred to as backwater as in water surface profiles.
BASEFLOW
Streamflow which results from precipitation that infiltrates into the soil eventually moving through the soil to the stream channel. This is also referred to as ground water flow, or dry-weather flow.
BASIN
An area having a common outlet to which surface runoff flows.
BILINEAR
The term bilinear is referring to a bilinear interpolation. This is simply an interpolation with two variables instead of one.
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BINARY
Based upon the integer two. Binary Code is composed of a combination of entities that can assume one of two possible conditions (0 or 1). An example in binary notation of the digits 111 would represent (1 X 2) + (1 X 2) + (1 X 2) = 4 + 2 + 1 = 7.
CALIBRATION
The process of using historical data to estimate parameters in a hydrologic forecast technique.
CARTOGRAPHIC
Pertaining to cartography, the art or practice of making charts or maps.
CASC2D
A physics-based distributed hydrologic model employing the finite difference method to solve the diffusive wave equations describing surface runoff developed by Pierre Y. Julien and Bahram Saghafian. See also,
Julien, P. Y., and B. Saghafian, 1991, CASC2D users manual - A two dimensional watershed rainfall-runoff model, Civil Engr. Report, CER90-91PYJ-BS-12, Colorado State University, Fort Collins, CO.
Julien, P. Y., Saghafian, B., and F. L. Ogden, 1995, “Raster-Based Hydrologic Modeling of Spatially-Varied Surface Runoff”, Water Resources Bulletin, AWRA, 31(3): 523-536.
CHANNEL INFLOW
Water, which at any instant, is flowing into the channel system from surface flow, subsurface flow, base flow, and rainfall that has directly fallen onto the channel.
CHANNEL ROUTING
The process of determining progressively timing and shape of the flood wave at successive points along a river.
CONCEPTUAL MODELS
Conceptual rainfall runoff models represent hydrological processes by mathematical equations conceived as storage terms. These equations
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involve parameters which are calibrated by comparing model outputs to observed outputs. The value of parameters may not have sound physical significance.
CONFORMAL PROJECTION
A projection that preserves the orthogonal relationship between parallels and meridians. The local angle on the Earth’s surface where a meridian crosses a latitude at a right angle is preserved in the projected map.
CONTOUR
Imaginary line on the ground, all points of which are at the same elevation above or below a specified datum.
CORRELATION DISTANCE
Correlation distance is the length scale that separates whether sampled values appear to be correlated or independent.
COVARIANCE MATRIX
A matrix containing the expected values derived from the products of the deviations of pairs of random variables from their means. Covariance measures the extent to which two random numbers vary together (i.e., varying at the same rate in the same direction).
CRUSTING
Crusting results from raindrop impact disaggregating the soil into constituent particles. The dislodged and disaggregated sand, silt and clay particles settle into the soil pores or are transported by the runoff downstream. The soil particles that settle into the surface form the crust.
CONSERVATION OF ENERGY
A law of physics that states that energy can not be created or destroyed only converted from one form to another.
CONSERVATION OF MASS
A law of physics that states that mass can not be created or destroyed only transferred from one volume to another.
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CONSERVATION OF MOMENTUM
A law of physics that states that an object in motion will stay in motion until acted upon by an outside force; an object at rest will remain at rest until acted upon by an outside force.
CUBIC SPLINES
A cubic spline is a spline constructed of piecewise third-order polynomials which pass through a set of control points. The second derivative of each polynomial is commonly set to zero at the endpoints, since this provides a boundary condition that completes the system of equations, leading to a simple 3-diagonal system which can be solved easily to give the coefficients of the polynomials. However, this choice is not the only one possible, and other boundary conditions can be used instead.
DATUM
In surveying, a reference system for computing or correlating the results of surveys. There are two principal types of datums: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted vertical datum for leveling operations is the national geodetic vertical datums of 1929 (differing slightly from mean sea level). The horizontal datum, used as a reference for position, is defined by: the latitude and longitude of an initial point, the direction of a line between this point and a specified second point, and two dimensions which define the spheroid. In the United States, the initial point for the horizontal datum is located at Meades Ranch in Kansas.
DEM--Digital Elevation Models
The U.S. Geological Survey produces five primary types of digital elevation model data. They are:
7.5-minute DEM (30- x 30-m data spacing, cast on Universal Transverse Mercator (UTM) projection or 1- x 1-arc-second data spacing). Provides coverage in 7.5- x 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute map series quadrangle. Coverage: Contiguous United States, Hawaii, and Puerto Rico.
1-degree DEM (3- x 3-arc-second data spacing). Provides coverage in 1- x 1-degree blocks. Two products (three in some regions of Alaska) provide the same coverage as a standard USGS 1-x 2-degree map series
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quadrangle. The basic elevation model is produced by or for the Defense Mapping Agency (DMA), but is distributed by USGS in the DEM data record format. Coverage: United States.
30-minute DEM (2- x 2-arc-second data spacing). Consists of four 15- x 15-minute DEM blocks. Two 30-minute DEMs provide the same coverage as a standard USGS 30- x 60-minute map series quadrangle. Saleable units will be 30- x 30-minute blocks, that is, four 15- x 15-minute DEMs representing one half of a 1:100 000-scale map. Coverage: Contiguous United States, Hawaii.
15-minute Alaska DEM (2- x 3-arc-second data spacing, latitude by longitude). Provides coverage similar to a 15-minute DEM, except that the longitudinal cell limits vary from 20 minutes at the southernmost latitude of Alaska to 36 minutes at the northern most latitude limits of Alaska. Coverage of one DEM will generally correspond to a 1:63,360-scale quadrangle.
7.5-minute Alaska DEM (1- x 2-arc-second data spacing, latitude by longitude). Provides coverage similar to a 7.5-minute DEM, except that the longitudinal cell limits vary from 10 minutes at the southernmost latitude of Alaska to 18 minutes at the northernmost latitude limits of Alaska.
DEVELOPABLE SURFACE
A surface when made tangent to the spheroid maybe flattened into a two dimensional surface without distortion. The direction of least distortion in the map projection is determined by the orientation of the developable surface.
DIGITAL TERRAIN ELEVATION DATA (DTED)
Digital Terrain Elevation Data (DTED), is an evenly spaced grid of points on the Earth’s surface at which elevations have been recorded. See also DEM.
DRAINAGE BASIN
A part of the surface of the Earth that is occupied by a drainage system, which consists of a surface stream or a body of impounded surface water together with all tributary surface streams and bodies of impounded surface water. Geographic area or region containing one or more drainage areas that discharge runoff to a single point.
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DTM—Digital Terrain Model
A DTM is a land surface represented in digital form by an elevation grid or lists of three-dimensional coordinates. Other attributes besides elevation can be derived to form a model of the terrain, e.g., slope and curvature.
DUNNE RUNOFF
A runoff process first identified by Thomas Dunne. Also known as saturation excess, where runoff is generated when the soil profile is filled or saturated.
FGDC--Federal Geographic Data Committee
The FGDC provides Federal leadership in the evolution of the National Spatial Data Infrastructure (NSDI) in cooperation with State and local governments, academia, and the private sector. The FGDC was established through the U.S. Office of Management and Budget (OMB) Circular A-16 and charged with the responsibility to coordinate various surveying, mapping, and spatial data activities of Federal agencies to meet the needs of the United States. Major objectives of Circular A-16 are to avoid duplication and minimize costs in mapping and spatial data activities of the Federal Government, which involves establishing standards and providing wider access to geospatial data. The FGDC also has been charged with coordinating geospatial data related activities with other levels of government and other sectors.
FINITE ELEMENT METHOD
A numerical method for solving differential equations. Differential operators are approximated with basis functions while minimizing residual errors over the solution domain. Assembly of element contributions produces a system of equations approximating the original differential equation. Commonly used in engineering mechanics to solve conservation equations, design structural members, and heat and mass transfer.
FLASH FLOOD
A flood which follows within a few hours (usually less than 6 hours) of heavy or excessive rainfall, dam or levee failure, or the sudden release of water impounded by an ice jam. Definitions vary in terms of response time. Often referred to as shorter in duration and response time than
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riverine floods where water tends to rise and recede slowly on the order of days.
FORECAST CREST
The highest elevation of river level, or stage, expected during a specified storm event.
FRACTAL
Fractal may be defined as a geometric set consisting of points, lines, areas or volumes whose measure is non-integer.
GAUGE
A device for indicating the magnitude or position of a thing in specific units, when such magnitude or position undergoes change, for example: The elevation of a water surface, the velocity of flowing water, the pressure of water, the amount or intensity of precipitation, the depth of snowfall, etc.
GAUGING STATION
A particular site on a watercourse where systematic observations of stage and/or flow are measured.
GEODETIC
Of or determined by geodesy; that part of applied mathematics which deals with the determination of the magnitude and figure either of the whole Earth or of a large portion of its surface. Also refers to the exact location points on the Earth’s surface accounting for curvature as opposed to a planar coordinate system.
GEOREGISTERED
An image that has been geographically referenced or rectified to an elevation model within a map projection. Sometimes referred to as geocoded or geometric registration.
GIS—Geographic Information System
A system, usually computer based, for the input, storage, retrieval, analysis and display of interpreted geographic data. The database is typically composed of map-like spatial representations, often called coverages or layers. These layers may involve a three-dimensional
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matrix of time, location, and attribute or activity. A GIS may include digital line graph (DLG) data, digital elevation models (DEM), geographic names, land-use characterizations, land ownership, land cover, registered satellite and/or aerial photography along with any other associated or derived geographic data.
GMT--Greenwich Mean Time
GMT is the mean solar time of the meridian of Greenwich used as the prime basis of standard time throughout the world. Also referred to as Universal Coordinated Time (UTC) or Zulu time (Z).
GPS--Global Positioning System
GPS is a worldwide satellite navigation system that is funded and supervised by the U.S. Department of Defense. GPS satellites transmit specially coded signals. These signals are processed by a GPS receiver that computes extremely accurate measurements, including 3-dimensional position, velocity, and time on a continuous basis.
GRASS--Geographic Resources Analysis Support System
GRASS is a product of the U.S. Army Corps of Engineers Construction Engineering Research Laboratories (USACERL) in Champaign, Illinois. It is an integrated set of programs designed to provide digitizing, image processing, map production, and geographic information system capabilities to its users. GRASS is an open sotware with freely available source code written in c.
DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement.
HEC-HMS
The Hydrologic Modeling System (HEC-HMS) is the ‘new generation” software developed for precipitation-runoff simulation HEC-HMS provides a variety of options for simulating precipitation-runoff processes. The software is designed for interactive use in a multi-tasking, multi-user network environment, and can be used with both X-Windows and Microsoft Windows. HEC-HMS is comprised of a graphical user interface (GUI), integrated hydrologic analysis components, data storage and management capabilities, and graphics and reporting facilities.
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HEC-HMS functions on a variety of platforms, including those that utilize Windows 3.1, Windows 95, Windows NT and X-Windows (i.e., UNIX-based workstations). The program is written in C++ and utilizes several libraries, some of which contain routines written in Fortran and C.
HORTONIAN RUNOFF
First identified by Robert E. Horton. Also known as infiltration excess. It is the runoff component resulting when the rainfall rate exceeds the potential infiltration rate of the soil. He developed four laws relating watershed properties to maximum runoff and flood generation: the law of stream numbers, the law of stream lengths, limiting infiltration capacity, and the runoff-detention-storage relation.
HRAP
A coordinate system used by the US NWS to map radar estimates of rainfall on a national grid. The standard longitude is at 105ºW with a grid positioned such that HRAP coordinates of the North Pole are at (401,1601). The grid resolution varies with latitude but is 4.7625 km at 60ºN latitude.
HYDROLOGY
Scientific study of the waters of the Earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water on or below the land surface.
HYDROLOGIC MODEL
A conceptual or physics-based procedure for numerically simulating a process or processes, which occur in a watershed.
HYDROLOGIC UNIT
A geographical area representing part or all of a surface drainage basin or distinct hydrologic feature such as a reservoir, lake, etc.
HYETOGRAPH
A graphical representation of rainfall intensity with respect to time.
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INFILTRATION
Movement of water through the soil surface into the soil.
INFILTRATION CAPACITY
The maximum rate at which water can enter the soil at a particular point under a given set of conditions.
INFILTRATION RATE
The rate at which infiltration takes place expressed in depth of water per unit time.
INTERPOLATE
To insert a value between known values by using a procedure or algorithm specifically related to the known values.
KRIGING
Surface interpolation technique that employs a statistical model of the variance to form an estimate at a particular location.
LAMBERT AZIMUTHAL EQUAL AREA PROJECTION
Azimuthal projections are formed onto a plane that is usually tangent to the globe at either pole, equator, or any intermediate point. The Lambert Azimuthal Equal Area projection is a method of projecting maps on which the azimuth or direction from a given central point to any other point is shown correctly and also on which the areas of all regions are shown in the same proportion of their true areas. When a pole is the central point, all meridians are spaced at their true angles and are straight radii of concentric circles that represent the parallels.
This projection is frequently used in one of three aspects: The polar aspect is used in atlases for maps of polar regions and of the Northern and Southern Hemispheres; the equatorial aspect is commonly used for atlas maps of the Eastern and Western Hemispheres; and the oblique aspect is used for atlas maps of continents and oceans.
LAMBERT CONFORMAL CONIC PROJECTION
The Lambert Conformal Conic Projection is derived by the projection of lines from the center of the globe onto a simple cone. This cone intersects the Earth along two standard parallels of latitude, both of
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which are on the same side of the equator. All meridians are converging straight lines that meet at a common point beyond the limits of the map. Parallels are concentric circles whose center is at the intersection point of the meridians. Parallels and meridians cross at right angles, an essential of conformality.
To minimize and distribute scale errors, the two standard parallels are chosen to enclose two-thirds of the north to south map area. Between these parallels, the scale will be too small, and beyond them, too large. If the north to south extent of the mapping is limited, maximum scale errors will rarely exceed one percent. Area exaggeration between and near the standard parallels is very slight; thus, the projection provides good directional and shape relationships for areas having their long axes running in an east to west orientation.
LULC
Land use Land cover (LULC) maps developed by the U.S. Geological survey. The set of Land Use and Land cover and associated maps consists of Land Cover, political units, hydrologic units, census county subdivisions, Federal land ownership, and State land ownership. The associated maps portray either natural or administrative information. They provide the user with the opportunity to utilize the Land Use and Land Cover maps and data, either individually or collectively, to produce graphic or tabular data for the areas portrayed on the associated maps. This mapping system is constructed in such a way that the Land Use and Land cover data can be related to other resource fields such as soils, geology, hydrology, and demography.
MIADS
Map Information Assembly and Display System is a data set that contains a three-layer composite of data derived from county soil surveys, gridded using a 200-meter grid increment. It covers all of Oklahoma except for the panhandle region west of about 1000Wlongitude.
MERCATOR PROJECTION
Mercator is a conformal map projection, that is, it preserves angular relationships. Mercator was designed and is recommended for navigational use and is the standard for marine charts. Mercator is often and inappropriately used as a world map projection in atlases and for
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wall charts where it presents a misleading view of the world because of the excessive distortion of area in the higher latitude areas.
MORAN INDEX
Moran introduced the first measure of spatial autocorrelation in order to study stochastic phenomena, which are distributed in space in two or more dimensions. The index is essentially a correlation coefficient evaluated for a group of adjacent or closely spaced data values. See Chapter 4 for details.
NAD27--North American Datum of 1927
NAD27 is defined with an initial point at Meads Ranch, Kansas, and by the parameters of the Clarke 1866 ellipsoid. The location of features on USGS topographic maps, including the definition of 7.5-minute quadrangle corners, are referenced to the NAD27.
NAD83--North American Datum of 1983
NAD83 is an Earth-centered datum and uses the Geodetic Reference System 1980 (GRS 80) ellipsoid, unlike NAD27, which is based on an initial point (Meades Ranch, Kansas). Using recent measurements with modern geodetic, gravimetric, astrodynamic, and astronomic instruments, the GRS 80 ellipsoid has been defined as a best fit to the worldwide geoid. Because the NAD83 surface deviates from the NAD27 surface, the position of a point based on the two reference datums will be different.
NEXRAD (NEXT-GENERATION WEATHER RADAR)
Network of high-resolution Doppler radars operated by the NWS; NEXRAD radar units are also known as WSR-88D. See Chapter 8 for details.
NOAA--National Oceanic and Atmospheric Administration
The NOAA, under the Department of Commerce, operates the civil polar-orbiting and geo-stationary satellite systems for the collection of atmospheric and environmental data, is the research agency supporting the NWS mission.
NWS--National Weather Service
The National Weather Service provides weather, hydrologic, and climate forecasts and warnings for the US, its territories, adjacent waters and
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ocean areas, for the protection of life and property and the enhancement of the national economy. NWS data and products form a national information database and infrastructure which can be used by other governmental agencies, the private sector, the public, and the global community.
NRCS—Natural Resources Conservation Service
The mission of NRCS is to provide leadership in a partnership effort to help people conserve, improve and sustain our natural resources and environment. NRCS has primary responsibility in the US for the small dam program known as PL 566, mapping soils, and developing soil and natural resource conservation plans.
OBLIQUE PROJECTION
A projection where the axis of the developable surface and the Earth’s axis form an oblique angle.
ORTHOPHOTO
Aerial photograph that has been adjusted or rectified to a georeferenced coordinate system. Other geographic features are correctly aligned when overlayed on such a photograph provided data is in the same datum and corrected for scale.
PARTIAL DISCRETIZATION
An approximation where not all of the differential operators are replaced with basis functions in the finite element method. Flow in the principal direction of slope may be approximated with a single gradient provided one-dimensional finite elements are laid out such that there are no gradients in other directions. This simplification reduces the numbers of matrices by computing gradients consistent with the kinematic wave equations.
PHYSICALLY REALISTIC
Parameters may be distorted due to resolution effects yet produce predictable behavior in physics-based models even though parameter values are unrealistic. For example, through calibration, hydraulic roughness is adjusted within a physically realistic range of values to attenuate and delay peak flow.
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POINT DATA
Point data refers to the representation of a quantity at a location without spatial extent.
PROJECTION
An orderly system of lines on a plane representing a corresponding system of imaginary lines on an adopted terrestrial or celestial datum surface. Also, the mathematical concept of such a system. For maps of the Earth, a projection consists of (1) a graticule of lines representing parallels of latitude and meridians of longitude or (2) a grid.
QUANTITATIVE PRECIPITATION FORECAST (QPF)
A NWS product used in forecasting precipitation. A spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a specified region, or area in probabilistic terms.
QUANTITATIVE PRECIPITATION ESTIMATE (QPE)
A spatial and temporal precipitation estimate derived from single or multisensor platforms for a specified region.
QUANTIZATION
The difference between one level contour and another. Refers to the precision of a continuous spectrum of a quantity such as precipitation, reflectivity, or elevation.
R.WATER.FEA
An interactive program that allows the user to simulate storm water runoff analysis using the finite element numerical technique. Infiltration is calculated using the Green and Ampt formulation. r.water.fea
computes and draws hydrographs for every basin as well as at stream junctions in an analysis area. It also draws animation maps at the basin level. Primarily described by the authors, Baxter E. Vieux and Nalneesh Gaur in the following:
Vieux, B.E. and N. Gaur, (1994), “Finite Element Modeling of Storm Water Runoff Using GRASS GIS,” Microcomputers in Civil Engineering, 9(4):263-270.
Arc.Water.Fea is an ArcView Extension that serves as an interface to the r.water.fea model.
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RADAR
Acronym for RAdio Detection And Ranging; a radio device or system for locating an object by means of ultrahigh-frequency radio waves reflected from the object and received, observed, and analyzed by the receiving part of the device in such a way that characteristics (as distance and direction) of the object may be determined.
RAIN GAUGE
Instrument for measuring the quantity of rain that has fallen at a point location.
RASTER
A raster image is a matrix of row and column data points whose values represent energy being reflected or emitted from the object being viewed by a remote sensing platform, e.g. a satellite. These values, or pixels, can be viewed on a display monitor as a black and white or color image. Rasters form a data format for representing data other than remotely sensed.
REFERENCE LATITUDE
Projection parameter that depends on location and extent of features to be mapped.
REFLECTIVITY
Radar term referring to the ability of a radar target to return energy; used to derive echo intensity and to estimate precipitation intensity and rainfall rates.
REFLECTIVITY FACTOR
Result of a mathematical equation (called the Weather Radar Equation) that converts the analog power (in Watts) received by the radar antenna into a more usable quantity. The reflectivity factor (denoted by Z) takes into account several factors, including the distance of a target from the radar, the wavelength of the transmitted radiation, and certain assumptions about the kind and size of targets detected by the radar. The reflectivity factor ranges over several orders of magnitudes, so it is
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usually expressed on a logarithmic scale called dbz (decibels of reflectivity).
RPG
Acronym for Radar Product Generator. The RPG is the computer in the NEXRAD system that receives polar-coordinate base radar data from the RDA and processes these data into end-user products. Algorithms are utilized for pattern-recognition, rainfall estimation, computation of VIL and other products. The RPG communicates these products to end-users.
Stage I Precipitation Processing : The first level of precipitation processing, occurring within the WSR-88D computer and performance for each volume scan of the radar. Base reflectivity data are converted to a precipitation estimate for each grid in the radar umbrella using a complex algorithm that includes quality control procedures, a Z/R relationship, and a bias adjustment using data from a ground-based precipitation gage network. Several graphical and digital products are produced for Weather Forecast Offices (WFO) operations and subsequent processing.
Stage II Precipitation Processing : The second level of precipitation processing, occurring within the WFO Advanced Weather Interactive Processing System (AWIPS) and performed on an hourly basis. Stage I precipitation estimates are further refined using data from additional precipitation gages and other sources such as rain/no rain determinations from satellite imagery. Stage II may also be executed at RFCs for backup purposes.
Stage III Precipitation Processing : The third level of precipitation processing, performed interactively at RFCs. Stage II precipitation estimates from multiple radars are mosaicked into an RFC area-wide product for use in river basin hydrologic modeling operations. RFC forecasters can review the mosaicked product, interactively edit areas of bad data, and substitute gage-only fields into portions of the mosaicked radar based product.
Stage IV Precipitation Processing : The fourth level of precipitation processing, performed automatically and/or interactively at NCEP. Stage III precipitation estimates from RFCs are mosaicked into a Nation-wide product for use in various real-time forecast activities and forecast verification operations.
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SAHEL
A geographic region of semi-arid lands bordering the southern edge of the Sahara Desert in Africa. It is characterized by a long dry season and a short wet season from July to September.
SCS--Soil Conservation Service
The U.S. Department of Agriculture’s Soil Conservation Service changed its name in 1995 to National Resources Conservation Service (NRCS). NRCS is the chief soil mapping agency in the U.S. Conservation programs include flood and erosion control.
SEMIVARIOGRAM
Mathematical model that describes spatial dependence or autocorrelation. Used in geostatistics and Kriging to assign weights when interpolating a surface.
SHADED RELIEF
Shading added to an image that makes the image appear to have three-dimensional aspects. This type of enhancement is commonly applied to digital topographic data to provide the appearance of terrain relief within the image.
SINKS
Interrupted drainage develops on limestone or dolomite beds through the dissolving action of water on the formation. Consequently, streams can disappear into subterranean caverns, often not re-emerging until they have traveled underground for a considerable distance. The term sink (or sinkhole) or karst drainage is sometimes used to describe this unusual stream pattern. Artifacts in digital elevation data where water appears not to drain is analogously referred to as a sink.
SOIL CLASSIFICATION
The systematic arrangement of soils into groups or categories based on their characteristics. Broad groupings are made on the basis of general characteristics and subdivisions on the premise of more detailed differences in specific properties.
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SOIL MAPPING UNIT
It is the smallest unit on a soil map that can be assigned a set of representative properties.
SOIL PHASE
A subdivision of a soil classification, usually a soil series or other unit based on characteristics that affect the use and management of the soil but which do not vary sufficiently to differentiate it as a separate soil series.
SOIL SLOPE
The degree of deviation of a surface from horizontal that is measured as a percentage, a numerical ratio, or in degrees.
SOIL TEXTURE
The relative proportions of sand, silt, and clay separates in a soil as described by the classes of soil texture.
SPHEROID
Mathematical figure closely approaching the geoid in form and size and used as a surface of reference for geodetic surveys. A reference spheroid or ellipsoid is a spheroid determined by revolving an ellipse about its shorter (polar) axis and used as a base for geodetic surveys of a large section of the Earth (such as the Clarke spheroid of 1866 which is used for geodetic surveys in the United States).
SPLINES
An interpolating polynomial that uses information from neighboring points to obtain a degree of global smoothness.
STATSGO--State Soil Geographic
The STATSGO is a State soil geographic database designed primarily for regional, multi-State, river basin, State, and multi-county resource planning, management, and monitoring. These data are not detailed enough to make interpretations at a county level. Detailed county-level soil surveys are not generally available in digital form.
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STEREOGRAPHIC PROJECTION
A projection that maps points on the Earth’s surface onto a plane tangent to a point on the spheroid. Circles and angles are preserved making the projection conformal.
STORM HYDROGRAPH
A hydrograph representing the total flow or discharge at a point in a stream or river in response to rainfall excess.
SURFACE RUNOFF
The runoff that travels overland to the stream channel. Rain that falls on the stream channel is often lumped with this quantity.
TENT POLE EFFECT
Artifact of some surfacing algorithms where the sparseness of the data produces unrealistic surface features similar to the fabric of a tent supported by poles.
THEMATIC DATA
Thematic data layers in a data set are layers of information that deal with a particular theme. These layers are typically related information that logically go together. Examples of thematic data would include a data layer whose contents are roads, railways, and river navigation routes.
THIN PLATE SPLINES
The thin plate spline is the two-dimensional analog of the cubic spline in 1-D. It is the fundamental solution to the biharmonic equation. Given a set of data points, a weighted combination of thin plate splines centered about each data point gives the interpolation function that passes through the points exactly while minimizing the so-called “bending energy.” Bending energy is defined here as the integral over of the squares of the second derivatives, Regularization may be used to relax the requirement that the interpolant pass through the data points exactly.
The name “thin plate spline” refers to a physical analogy involving the bending of a thin sheet of metal. In the physical setting, the deflection is in the direction, orthogonal to the plane. In order to apply this idea to the problem of coordinate transformation, one interprets the lifting of the plate as a displacement of the coordinates within the plane. Thus, in
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general, two thin plate splines are needed to specify a 2-D coordinate transformation.
TIN
Triangular irregular network comprised of triangles or facets representing a surface such as topography.
TOPMODEL
TOPMODEL predicts catchment water discharge and spatial soil water saturation pattern based on precipitation and evapotranspiration time series and topographic information.
TOPOGRAPHIC MAP
Map that presents the horizontal and vertical positions of the features represented; distinguished from a planimetric map by the addition of relief in measurable form.
TOPOGRAPHY
Configuration (relief) of the land surface; the graphic delineation or portrayal of that configuration in map form, as by contour lines; in oceanography the term is applied to a surface such as the sea bottom or a surface of given characteristics within the water mass.
TOPOLOGICALLY STRUCTURED
Refers to the point, line, or area features of a data set and the relationships between these features. These relationships are expressed as connections between spatially touching lines, small areas contained within larger areas, lines that make up the sides of an area or polygon, etc. Topology does not provide information as to the features’ meanings, only their identity and structural relationships as they define spatial objects.
TRANSVERSE PROJECTION
A transverse projection with a cylinder oriented such that the developable surface axis is at right angles to the Earth’s axis and is tangent to the Earth’s surface along some meridian.
283
302
UNIT HYDROGRAPH (UNITGRAPH)
The discharge hydrograph from one depth unit of surface runoff distributed uniformly over the entire basin for a given time period. Assumes a linear response from the system due to unit impulse.
UNIT HYDROGRAPH THEORY
Unit Hydrograph Theory states that surface runoff hydrographs for storm events of the same duration will have the same shape, and the ordinates of the hydrograph will be proportional to the ordinates of the unit hydrograph.
USGS--United States Geological Survey
Established in March of 1879, the Geological Survey’s primary responsibilities are: investigating and assessing the Nation’s land, water, energy, and mineral resources; conducting research on global change; investigating natural hazards such as earthquakes, volcanos, landslides, floods, and droughts; and conducting the National Mapping Program. To attain these objectives, the Geological Survey prepares maps and digital and cartographic data; collects and interprets data on energy and mineral resources; conducts nationwide assessments of the quality, quantity, and use of the Nation’s water resource; performs fundamental and applied research in the sciences and techniques involved; and publishes and disseminates the results of its investigations in thousands of new maps and reports each year.
UTM--Universal Transverse Mercator Projection
UTM is a widely used map projection that employs a series of identical projections around the world in the mid-latitude areas, each spanning six degrees of longitude and oriented to a meridian. This projection is characterized by its conformality; that is, it preserves angular relationships and scale plus it easily allows a rectangular grid to be superimposed on it. Many worldwide topographic and planimetric maps at scales ranging between 1:24 000 and 1:250 000 use this projection.
VARIOGRAM
See semivariogram.
284
303
VCP
Acronym for Volume Coverage Pattern. The VCP is the sequence of elevation angles that a NEXRAD radar is programmed to use to scan the atmosphere. The NEXRAD operator can choose to scan using one of four possible VCPs. The duration for completing the volume scan determines the timestep or interval of the precipitation estimate.
Vflo™
Commercially available distributed model that is fully distributed and physics-based. Finite elements are used to solve the kinematic wave equations to generate flow rates at any location in a drainage network. Geospatial data is imported using ASCII grids or via an ArcGIS extension. Post-analysis and real-time applications hydrologic analysis and prediction is supported on Linux and Windows operating systems.
WATERSHED
Land area from which water drains toward a common watercourse or point. See the term BASIN.
WGS 72--World Geodetic System 1972
WGS 72 is an Earth-centered datum, and was the result of an extensive effort extending over approximately three years to collect selected satellite, surface gravity, and astrogeodetic data available throughout 1972. These data were combined using a unified WGS solution (a large-scale least squares adjustment).
WGS 84--World Geodetic System 1984
The WGS 84 datum was developed as a replacement for WGS 72 by the military mapping community as a result of new and more accurate instrumentation and a more comprehensive control network of ground stations. The newly developed satellite radar altimeter was used to deduce geoid heights from oceanic regions between 70 degrees north and south latitude. Geoid heights were also deduced from ground-based Doppler and ground-based laser satellite-tracking data, as well as surface gravity data. This system is described in “World Geodetic System 1984,” DOD DMA TR 8350.2 September 1987. New and more extensive data sets and improved software were used in the development.
285
304
WRS—Worldwide Reference System
The WRS is a global indexing scheme designed for the Landsat program based on nominal scene centers defined by path and row coordinates.
WSR-88D
A Doppler radar termed the Weather Surveillance Radar prototyped in 1988 at the NOAA-National Severe Storms Laboratory, Norman Oklahoma.
Z-R RELATIONSHIP
Mathematical equation that converts radar-measured reflectivity to an estimated rainfall rate. The reflectivity factor (Z) is related to both the drop size distribution and the 6th power of the drop diameters. However, the radar only measures reflectivity, not the drop size distribution. Hence, the drop size distribution must be assumed and then the resulting rainfall amounts adjusted using rain gauge accumulations. Different drop size distributions can produce the same reflectivity factor, but with markedly different rainfall rates. For example, many small drops can produce the same reflectivity as one large drop; however, the rainfall rate from the small drops is very different from the one large drop.
286
Index
adjoint 201; 206; 209
aerial photography 44
albers equal area projection 263
ANSWERS 122
ARC/INFO See Glossary
ArcGIS 48; 179; 180; 241; 242; 264; 285
ArcView 37; 48; 264; 277
aspect 33; 48; 131
basin 5; 15; 37; 59; 75; 116; 131
bubbling pressure 104
calibration 201; 265
cartographic 265
CASC2D 9; 265
channel inflow 265
CHANNEL ROUTING 265
conceptual models 208; 265
conformal projection 26; 266
conservation of energy 266
conservation of mass 6; 74; 182; 184; 266
conservation of momentum 267
contour 21; 32; 33; 34; 35; 40; 266
cost function 202; 204; 210
Courant condition 191
cross-validation 53; 57; 65; 70
crusting 94; 266
cubic splines 61; 267
cumulative rainfall 103; 120
data structure 9; 21; 33; 37; 44; 130
datum 24; 267; 275
decorrelation length 154
degree of saturation 12; 102; 205
DEM 15; 32; 35; 38; 40; 41; 42; 267
deterministic models 145
developable surface 29; 268
digital elevation model See DEM
digital terrain elevation data See DTEM
digital terrain model See DTM
dimensionality 23
distributed hydrologic model 3; 4; 9; 45
drainage basin 133; 268
drainage length 15; 83
drainage network 37; 42; 83; 130
DTED 33
DTM 33
Dunne 13; 269
effective porosity See porosity. See
porosity
evapotranspiration 8; 22
FGDC 31; 269
finite element method 184; 187; 211; 269;
276
flash flood 269
flood 93; 167; 269
288 Contents
fractal 80; 270
gauge 150; 270
gauge network density 151
GAUGING STATION 270
geodetic 270.
geographic information system 1; 263;
270
georeference 25
Georeferenced Coordinate Systems 26
georegistered 270
GIS See geographic information system
global positioning system 271
GMT 271
GPS 271
GRASS 271
Green-Ampt 92; 93; 96; 97; 101; 103;
108
GSSHA 9
HEC-HMS 271
Hortonian 11; 272
HRAP 27
hydraulic conductivity 93; 94; 96; 103;
106
hydrograph 201
hydrologic model 2; 6; 16; 22; 45
hydrologic unit 272
HYDROLOGY 272
HYETOGRAPH 272
IDW 50
infiltration 273
INFILTRATION CAPACITY 273
Infiltration Excess (Hortonian) See
Infiltration
infiltration rate 11; 92; 101; 273
interpolate 10; 50; 51; 53; 57; 273
inverse distance weighting interpolation
See IDW
isohyet 32
kinematic wave analogy 182
Kriging 10; 49; 50; 53
lambert azimuthal equal area projection
273
lambert conformal conic projection 273
land use/cover 43; 44
LULC 123; 274
lumped model 1; 4; 201
Manning’s roughness 118
map See map projections
map projections 26
Map Projections 26
map scale 23; 130; 131
mercator 274; 284
metadata 31
MIADS 103; 106; 274
multiplicative bias correction 166
Nash-Sutcliffe statistic 205
NEXRAD 167; 275
NOAA 275
NRCS 276
nugget variance 56
NWS 275
oblique projection 276
orthophoto 25; 276
Orthophotography 25
ponding 102
pore size 104
porosity 7; 94; 102; 103
projection 26; 277
QPE 277
QPF 277
quantization 9; 33; 277
r.water.fea 8; 9; 16; 178; 179; 277
RADAR 275; 278
Radar Bias Adjustment 164
rain gauge 23; 154; 278
rain gauge network 151; 152; 153
random errors 132; 155; 160; 164; 174;
227
raster 33; 37; 278
reference latitude 28; 278
reflectivity 149; 155; 278
REFLECTIVITY FACTOR 278
RPG 170; 279
Sahel 66; 280
Contents 289
Saturation Excess (Dunne Type) See
infiltration
SCS 96; 280
semivariogram 53; 55; 57; 280
shaded relief 280
sinks 131; 280
slope 15; 32; 86; 138
soil classification 42; 280
soil conservation service See SCS
soil mapping unit 106; 281
soil texture 281
spheroid 26; 28
Splines See Also Thin Plate Splines,
Cubic Splines
standard error 96; 97; 109; 110; 152; 153;
165
STATSGO 103; 281
stereographic projection 27; 282
storm hydrograph 282
surface runoff 11; 92; 117; 282
systematic errors 17; 155; 156; 164; 172;
175; 227; 229; 237
tent pole effect 49; 52; 282
thematic data 282
Thiessen polygons 50; 150
thin plate splines 63; 282
TIN 21; 35; 283
TOPMODEL 83; 131; 283
topographic map 33; 45; 283
topography 1; 32; 283
topologically structured 283
transverse projection 29; 283
unit hydrograph 284
unit hydrograph theory 284
universal transverse mercator projection
See UTM
USGS 33; 44; 103; 123; 284
UTM 28; 29; 30; 284
variogram 53; 54; 60; 284
VCP 168; 285
Vflo™ xiv; 8; 9; 16; 17; 18; 20; 177; 179;
180; 196; 217; 218; 224; 227; 238;
239; 240; 241; 242; 243; 247; 248;
250; 252; 253; 256; 257; 258; 259;
260; 285
watershed 37; 285
wetting front 94; 99; 101; 205
WGS 72 See geodetic
WGS 84 See geodetic
WSR-88D 155; 167; 275; 286
Z-R relationship 156; 157; 160; 161; 162;
163; 171; 174; 225; 286
Water Science and Technology Library
1. A.S. Eikum and R.W. Seabloom (eds.): Alternative Wastewater Treatment. Low-CostSmall Systems, Research and Development. Proceedings of the Conference held inOslo, Norway (7–10 September 1981). 1982 ISBN 90-277-1430-4
2. W. Brutsaert and G.H. Jirka (eds.): Gas Transfer at Water Surfaces. 1984ISBN 90-277-1697-8
3. D.A. Kraijenhoff and J.R. Moll (eds.): River Flow Modelling and Forecasting. 1986ISBN 90-277-2082-7
4. World Meteorological Organization (ed.): Microprocessors in Operational Hydro-logy. Proceedings of a Conference held in Geneva (4–5 September 1984). 1986
ISBN 90-277-2156-45. J. Nemec: Hydrological Forecasting. Design and Operation of Hydrological Fore-
casting Systems. 1986 ISBN 90-277-2259-56. V.K. Gupta, I. Rodrıguez-Iturbe and E.F. Wood (eds.): Scale Problems in Hydrology.
Runoff Generation and Basin Response. 1986 ISBN 90-277-2258-77. D.C. Major and H.E. Schwarz: Large-Scale Regional Water Resources Planning. The
North Atlantic Regional Study. 1990 ISBN 0-7923-0711-98. W.H. Hager: Energy Dissipators and Hydraulic Jump. 1992 ISBN 0-7923-1508-19. V.P. Singh and M. Fiorentino (eds.): Entropy and Energy Dissipation in Water
Resources. 1992 ISBN 0-7923-1696-710. K.W. Hipel (ed.): Stochastic and Statistical Methods in Hydrology and Environmental
Engineering. A Four Volume Work Resulting from the International Conference inHonour of Professor T. E. Unny (21–23 June 1993). 199410/1: Extreme values: floods and droughts ISBN 0-7923-2756-X10/2: Stochastic and statistical modelling with groundwater and surface water applic-ations ISBN 0-7923-2757-810/3: Time series analysis in hydrology and environmental engineering
ISBN 0-7923-2758-610/4: Effective environmental management for sustainable development
ISBN 0-7923-2759-4Set 10/1–10/4: ISBN 0-7923-2760-8
11. S.N. Rodionov: Global and Regional Climate Interaction: The Caspian Sea Experi-ence. 1994 ISBN 0-7923-2784-5
12. A. Peters, G. Wittum, B. Herrling, U. Meissner, C.A. Brebbia, W.G. Gray and G.F.Pinder (eds.): Computational Methods in Water Resources X. 1994
Set 12/1–12/2: ISBN 0-7923-2937-613. C.B. Vreugdenhil: Numerical Methods for Shallow-Water Flow. 1994
ISBN 0-7923-3164-814. E. Cabrera and A.F. Vela (eds.): Improving Efficiency and Reliability in Water Dis-
tribution Systems. 1995 ISBN 0-7923-3536-815. V.P. Singh (ed.): Environmental Hydrology. 1995 ISBN 0-7923-3549-X16. V.P. Singh and B. Kumar (eds.): Proceedings of the International Conference on
Hydrology and Water Resources (New Delhi, 1993). 199616/1: Surface-water hydrology ISBN 0-7923-3650-X16/2: Subsurface-water hydrology ISBN 0-7923-3651-8
Water Science and Technology Library
16/3: Water-quality hydrology ISBN 0-7923-3652-616/4: Water resources planning and management ISBN 0-7923-3653-4Set 16/1–16/4 ISBN 0-7923-3654-2
17. V.P. Singh: Dam Breach Modeling Technology. 1996 ISBN 0-7923-3925-818. Z. Kaczmarek, K.M. Strzepek, L. Somlyody and V. Priazhinskaya (eds.): Water
Resources Management in the Face of Climatic/Hydrologic Uncertainties. 1996ISBN 0-7923-3927-4
19. V.P. Singh and W.H. Hager (eds.): Environmental Hydraulics. 1996ISBN 0-7923-3983-5
20. G.B. Engelen and F.H. Kloosterman: Hydrological Systems Analysis. Methods andApplications. 1996 ISBN 0-7923-3986-X
21. A.S. Issar and S.D. Resnick (eds.): Runoff, Infiltration and Subsurface Flow of Waterin Arid and Semi-Arid Regions. 1996 ISBN 0-7923-4034-5
22. M.B. Abbott and J.C. Refsgaard (eds.): Distributed Hydrological Modelling. 1996ISBN 0-7923-4042-6
23. J. Gottlieb and P. DuChateau (eds.): Parameter Identification and Inverse Problemsin Hydrology, Geology and Ecology. 1996 ISBN 0-7923-4089-2
24. V.P. Singh (ed.): Hydrology of Disasters. 1996 ISBN 0-7923-4092-225. A. Gianguzza, E. Pelizzetti and S. Sammartano (eds.): Marine Chemistry. An Envir-
onmental Analytical Chemistry Approach. 1997 ISBN 0-7923-4622-X26. V.P. Singh and M. Fiorentino (eds.): Geographical Information Systems in Hydrology.
1996 ISBN 0-7923-4226-727. N.B. Harmancioglu, V.P. Singh and M.N. Alpaslan (eds.): Environmental Data Man-
agement. 1998 ISBN 0-7923-4857-528. G. Gambolati (ed.): CENAS. Coastline Evolution of the Upper Adriatic Sea Due to
Sea Level Rise and Natural and Anthropogenic Land Subsidence. 1998ISBN 0-7923-5119-3
29. D. Stephenson: Water Supply Management. 1998 ISBN 0-7923-5136-330. V.P. Singh: Entropy-Based Parameter Estimation in Hydrology. 1998
ISBN 0-7923-5224-631. A.S. Issar and N. Brown (eds.): Water, Environment and Society in Times of Climatic
Change. 1998 ISBN 0-7923-5282-332. E. Cabrera and J. Garcıa-Serra (eds.): Drought Management Planning in Water Supply
Systems. 1999 ISBN 0-7923-5294-733. N.B. Harmancioglu, O. Fistikoglu, S.D. Ozkul, V.P. Singh and M.N. Alpaslan: Water
Quality Monitoring Network Design. 1999 ISBN 0-7923-5506-734. I. Stober and K. Bucher (eds): Hydrogeology of Crystalline Rocks. 2000
ISBN 0-7923-6082-635. J.S. Whitmore: Drought Management on Farmland. 2000 ISBN 0-7923-5998-436. R.S. Govindaraju and A. Ramachandra Rao (eds.): Artificial Neural Networks in
Hydrology. 2000 ISBN 0-7923-6226-837. P. Singh and V.P. Singh: Snow and Glacier Hydrology. 2001 ISBN 0-7923-6767-738. B.E. Vieux: Distributed Hydrologic Modeling Using GIS. 2001 ISBN 0-7923-7002-3
Water Science and Technology Library
39. I.V. Nagy, K. Asante-Duah and I. Zsuffa: Hydrological Dimensioning and Operationof Reservoirs. Practical Design Concepts and Principles. 2002 ISBN 1-4020-0438-9
40. I. Stober and K. Bucher (eds.): Water-Rock Interaction. 2002 ISBN 1-4020-0497-441. M. Shahin: Hydrology and Water Resources of Africa. 2002 ISBN 1-4020-0866-X42. S.K. Mishra and V.P. Singh: Soil Conservation Service Curve Number (SCS-CN)
Methodology. 2003 ISBN 1-4020-1132-643. C. Ray, G. Melin and R.B. Linsky (eds.): Riverbank Filtration. Improving Source-
Water Quality. 2003 ISBN 1-4020-1133-444. G. Rossi, A. Cancelliere, L.S. Pereira, T. Oweis, M. Shatanawi and A. Zairi (eds.):
Tools for Drought Mitigation in Mediterranean Regions. 2003 ISBN 1-4020-1140-745. A. Ramachandra Rao, K.H. Hamed and H.-L. Chen: Nonstationarities in Hydrologic
and Environmental Time Series. 2003 ISBN 1-4020-1297-746. D.E. Agthe, R.B. Billings and N. Buras (eds.): Managing Urban Water Supply. 2003
ISBN 1-4020-1720-047. V.P. Singh, N. Sharma and C.S.P. Ojha (eds.): The Brahmaputra Basin Water Resources.
2004 ISBN 1-4020-1737-548. B.E. Vieux: Distributed Hydrologic Modeling Using GIS. Second Edition. 2004
ISBN 1-4020-2459-249. M. Monirul Qader Mirza (ed.): The Ganges Water Diversion: Environmental Effects
and Implications. 2004 ISBN 1-4020-2479-7
Kluwer Academic Publishers – Dordrecht / Boston / London
