S.Mike Linhart and Kris D. Lund 2006 vector digital data Scientific Investigations Map 2006-2949-A Raleigh, NC U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?sim06-2949A_dar_bth_cont S.Mike Linhart and Kris D. Lund 2006 pdf document Scientific Investigations Map 2006-2949 Raleigh, NC U.S. Geological Survey http://pubs.water.usgs.gov/sim2006-2949 This data set consists of digital bathymetry contours for Lake Darling in Washington Co., Iowa. The U.S. Geological Survey conducted a bathymetric survey of Lake Darling in 2004. This digital, geographically referenced data set was developed by the U.S. Geological Survey to be used with the Lake Bathymetric project, Eastern Field Unit, Iowa City, Iowa. Data collected during the bathymetric survey were input into a geographic information system (GIS) software package, ArcInfo, to create a point coverage representing discrete point locations. The point coverage was then used to generate a three-dimensional surface representing the lake-bottom elevations. This surface was then contoured and the contours were then adjusted to correct for interpretive errors. 2004 ground condition Complete None planned -91.907820 -91.880071 41.203942 41.181579 None Lakes Bathymetry Contours InlandWaters Hydrology USGS None Lake Darling Washington County Iowa This digital, geographically referenced data set was developed by the U.S. Geological Survey to be used with the Lake Bathymetric project, Eastern Field Unit, Iowa City, Iowa. The data are released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. U.S. Geological Survey Greg Nalley Project Chief - Eastern Field Unit Supervisory Hydrologist mailing address

P.O. Box 1230

Iowa City Iowa 52244 USA 319-337-4191 319-358-3606 gmnalley@usgs.gov Compilation of this data set prepared in cooperation with Iowa Department of Natural Resources. Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.1.0.722 Topologically Clean Contours have been adjusted for interpretive errors and smoothed. Accuracy is tested by visual comparison of source with digital data on an interactive computer system. Iowa Department of Natural Resources Unknown 2002 remote-sensing image <http://www.igsb.uiowa.edu/nrgislibx/> Aerial Photo 2002 ground condition None Digital orthophoto quads (DOQ's) were used in further adjusting and smoothing the coverage of the lake boundary. The coverage was overlain on the DOQ and additional nodes were digitized in. Water-surface elevation: Initial measurements determined the elevation of the water surface of Lake Darling referenced to North American Vertical Datum (NAVD) of 1988. The water-surface elevation of Lake Darling was determined by tape down (using a steel tape) from a reference point (with a known elevation) on the boat slip structure near the boat ramp. The elevation of the reference point was obtained from the Washington County Engineering Department. The elevation of the reference point (chiseled arrow) was reported as 656.98 ft above NAVD88. The water-surface elevation was found to be 656.06 ft above NAVD88 on April 14, 2004. 2004 Data collection: Bathymetry data were collected using the Bathymetric Survey System (BSS+5) with a 200-kHZ intelligent depth sounder (IDS) and a differential GPS (Novatel DGPS beacon or Omnistar receiver) (Specialty Devices, Inc., 2003, Bathymetric Survey System BSS+5 with Omnistar manual: Specialty Devices, Inc., Plano, Texas, 38 p.). The depth sounder emits pulses of sound that are reflected off the lake bottom and are received by a transducer. The differential GPS has a horizontal accuracy of about 1 meter (3.281 ft). Bathymetry and position data were collected and stored in Hypack Max software (ver. 2.12a) (Hydrographic Survey Software, User's Manual, Hypack Max, Coastal Oceanographics, Inc., Middlefield, Conn.). In Hypack Max, the geodetic parameters were set to UTM north, Zone 15, and ellipsoid GRS-1980. Distance (easting and northing) and depth units were both collected in feet. Current limitations of the Bathymetric Survey System (BSS+5) restrict data collection to depths greater than approximately 3.3 ft. A bar check calibration on the echo sounder was performed at the start of each day following established protocols (U.S. Army Corps of Engineers, 1994, Engineering and design: Hydrographic survey EM 1110-2-1003, chap. 9-3, p. 9-4 to 9-9). This was done to ensure that the echo sounder was calibrated correctly. The bar check involves suspending a 2-ft-diameter flat aluminum plate directly below the echo sounder. The suspension line is marked in 5-ft increments. An initial calibration is made at 5 ft by entering the speed of sound in water and then adjusting the offset of the transducer in the computer software. The offset is the draft of the transducer below the lake surface. The aluminum plate is then lowered in 5-ft increments (depending on the range of depths expected to be encountered on the day of data collection) and adjustments in the speed of sound are made until depth readings and the depth of the aluminum plate agree to within approximately 0.1 ft. Data were collected along planned transect lines that were set-up in Hypack Max using the internal line editor prior to data collection. Transect lines were spaced at 150-ft intervals perpendicular to the long axis of Lake Darling. Transect lines also were located perpendicular to axis of the major north and south arms. Depending on boat speed, bathymetry data points were collected at approximately 5- to 15-ft intervals. Data points may be much closer in areas where transect or perimeter runs overlap. Perimeter bathymetry data points were collected while driving the boat around the perimeter of the lake. The distance of the boat from shore during the perimeter run varied, depending upon the depths encountered, due to the depth limitations of the data-collection equipment. The raw bathymetry data were recorded in Hypack Max as depths (in feet below water surface to the lake bottom). Target points were collected in areas of the lake where it was too shallow to collect data with the BSS+5 system. Target point depths were collected manually, using a measuring device marked in 0.10-ft increments, along with a corresponding easting and northing location. Depending on lake-bottom type and surface conditions of the lake, accuracy of these measurements can vary between 0.05 ft and 0.5 ft. The number and location of target points were based on a judgment made in the field that was thought to be spatially representative of the area. In addition, shore point locations (easting and northing) were collected to define the edge and islands of the lake. These locations are collected by touching the bow of the boat to the shoreline at various intervals along the shoreline and recording the position using a bow-mounted GPS antenna. 2004 Post-processing: Bathymetry data were processed using the Hypack Max software. Post-processing involved removing obvious spikes, inputting depths for the time-tagged target points, and editing extraneous points within the shore point files. In addition, tide corrections were applied in Hypack Max to convert raw sounding depths to elevation. The tide file subtracts the depths from the assigned lake-surface elevation (obtained from measurement from reference point elevation to lake water surface). The processed bathymetry data in Hypack Max were exported to XYZ format. A total of three separate files were exported into XYZ format: (1) the transect and perimeter bathymetric data; (2) the shore point location data; and (3) the target point data. All three XYZ files were then converted to ASCII text files for input into ESRI-ArcGIS (ver. 8.3). The data in the text file containing all the transect and perimeter data were weeded (using the text editor EMACS) from 7,405 to 2,454 data points (dar_tinpts.txt), to reduce the density of points in one direction (along data-collection transects) to minimize the spatial pull of contours toward the densified lines. 2004 Generation of Bathymetry Map: The text files (containing northing, easting, and elevation) were input into an arc macro language (AML) script called CREATEPOINT in ARC to generate three point coverages (dar_tinpts, dar_targpts, and dar_edgepts). The dar_tinpts coverage contains the weeded bathymetry points collected with the depth sounder. The dar_targpts coverage contains the bathymetry target points collected manually. The dar_edgepts coverage contains the shore point locations. The coverage dar_allpts was created from a text file of the unweeded data points but was not used in the generation of the bathymetry map. Projections for the coverages were defined in ARC as UTM zone 15, NAD83, with units in feet. A polygon coverage (dar_bndry) was then created for the lake shore by first connecting (digitizing in ArcEdit) the points in the dar_edgepts coverage. A digital orthophoto quad (DOQ) (Iowa Department of Natural Resources, 2002-2003, Iowa 2002 Digital Orthophoto Update Project, information available on World Wide Web at URL http://www.igsb.uiowa.edu/nrgislibx/) was later used as an aid in further adjusting the coverage of the shoreline. The coverage was then copied to a polyline coverage (dar_bndelev). In ARC, an elevation attribute (elev) was added to dar_bndelev.aat. In ArcEdit, the "elev" attribute was calculated to a value of 656.1 ft (lake-surface elevation, above NAVD88). A polygon coverage (dar_islands) was created to define the shoreline of the islands by digitizing (in ArcEdit) the necessary points in the dar_edgepts coverage. A digital orthophoto quad (DOQ) (Iowa Department of Natural Resources, 2002-2003, Iowa 2002 Digital Orthophoto Update Project, information available on World Wide Web at URL http://www.igsb.uiowa.edu/nrgislibx/) was later used as an aid in further adjusting the coverage of the shoreline of the islands. The coverage was then copied to a polyline coverage (dar_islelev). In ARC, an elevation attribute (elev) was added to dar_islelev.aat. In ArcEdit, the "elev" attribute was calculated to a value of 656.1 ft (lake-surface elevation, above NAVD88). To generate contours and calculate lake volume, three-dimensional surfaces (TIN models) were created using 3-D Analyst in ArcMap. The TIN (dar_tin) model was generated to create the preliminary contours. The TIN (dar_tin) model was generated using the dar_tinpts and dar_targpts point coverages triangulated as mass points. Height source was "elevation". The dar_bndelev arc and the dar_islelev arc were input as hard lines with a height source from the "elev" attribute (elevation value = 656.1 ft). The dar_bndry coverage (polygon) was input as a hard clip to clip the TIN to the lake shoreline. The dar_islands coverage was input into the TIN as a hard erase to clip out the islands. The shapefile (dar_brklines) was input into the TIN as a soft line, with no elevation attribute, in an attempt to reduce the amount of jaggedness in the preliminary contours. Two polyline coverages (dar_rchbrline and dar_lchbrline) were input into the TIN as soft lines to eliminate the "holes" created by widely separated target data points in the southeast and southwest channels. Elevation attributes "elev" were added to both the dar_rchbrline.aat and the dar_lchbrline.aat. The elev values for both coverages were given a value of 654.0 ft. Another TIN model (dar_tinsmooth) was later generated to re-calculate lake volume after the boundary coverages (dar_bndry, dar_bndelev, dar_islands, and dar_islelev) were further adjusted using a DOQ. The TIN (dar_tin) was used to generate the preliminary contours. Contours were generated in ARC using the TINCONTOUR command to generate the dar_bth_orig coverage. Contour intervals were set at 2 ft with a base contour of 641 ft. The minimum contour is 641 ft and the maximum contour is 655 ft. The coverage dar_bth_orig was then copied to dar_bth_cont. The dar_bth_cont coverage was the edit coverage in ArcEdit where the contours were smoothed and adjusted for interpretive errors. The dar_bth_orig coverage was used as a back coverage and for comparison during smoothing in ArcEdit. Most interpretive adjustments and smoothing were done manually by adding, moving, or deleting vertices as needed. For selected contours (arcs), grain size (using the GRAIN command) was set to 0.01. The SPLINE command was then issued. Then the grain size was set to 30 and splined again. The command UNSPLIT NONE was then issued to remove the pseudo nodes. For smaller contour arcs, (that is, those representing small enclosed areas), final grain size was usually set between 5 and 10. Contour movement was generally greatest in those contours with sharp bends using the GRAIN and SPLINE commands. Contours in the dar_bth_cont coverage were later further adjusted, primarily around the shorelines, after the boundary files were further adjusted using the DOQ, and the TIN (dar_tinsmooth) was generated. The contour interval does not reflect map accuracy. The volume for Lake Darling was calculated in ArcMap/3-D Analyst using the TIN (dar_tinsmooth). The volume was calculated above a reference plane (lake-surface elevation) of -656.1 ft. The TIN was inverted for calculation purposes only, following guidelines in ESRI-ArcGIS (ver. 8.3). ArcMap/3-D Analyst uses linear interpolation to calculate the area and volume of those portions of the TIN surface lying between the specified base value (lake-surface elevation) and the highest point in the TIN. Data from this survey show that the surface area of Lake Darling, at a water-surface elevation of 656.1 ft, is approximately 10,660,000 square feet (240 acres) and water volume of Lake Darling is approximately 83,924,000 cubic feet (1,930 acre-ft). Glossary: Bathymetry - Measurement of depths in water GPS - Global Positioning System NAVD88 - North American Vertical Datum of 1988 GIS - Geographic Information System NAD83 - North American Datum of 1983 UTM - Universal Transverse Mercator Easting and Northing - UTM coordinates TIN - Triangulated Irregular Network 2005-2006 Vector Complete chain 48 Point 4 Transverse Mercator 0.999600 -93.000000 0.000000 1640416.666667 0.000000 coordinate pair 0.000005 0.000005 survey feet North American Datum of 1983 Geodetic Reference System 80 6378137.000000 298.257222 North American Vertical Datum of 1988 2 feet Explicit elevation coordinate included with horizontal coordinates dar_bth_cont.aat Arc Attribute Table ARC/INFO(R) GIS Software FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape Feature geometry. ESRI Coordinates defining the features. FNODE# Internal node number for the beginning of an arc (from-node). ESRI Whole numbers that are automatically generated. TNODE# Internal node number for the end of an arc (to-node). ESRI Whole numbers that are automatically generated. LPOLY# Internal node number for the left polygon. ESRI Whole numbers that are automatically generated. RPOLY# Internal node number for the right polygon. ESRI Whole numbers that are automatically generated. LENGTH Length of feature in internal units. ESRI Positive real numbers that are automatically generated. DAR_BTH_CONT# Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. DAR_BTH_CONT-ID User-defined feature number. ESRI Integer n/a n/a CONTOUR Bathymetric contour, in feet User defined 641 655 feet 2 Value accuracy estimated. Contour accuracy was not evaluated. The contour interval does not reflect map accuracy. HACHURE Indicates closed low User defined y Indicates the presence of a closed low User defined n Closed low not present User defined U.S. Geological Survey Ask USGS - Water Webserver Team mailing address

445 National Center

Reston VA 20192 USA 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+sim06-2949A_dar_bth_cont None The Lake Bathymetric project of the Eastern Field Unit, Iowa Water Science Center, the Water Resources Discipline (WRD), and the U.S. Geological Survey make no guarantee nor offer any warranty concerning the accuracy, condition, or application of the information contained in these geographic data. The burden for determining fitness for use of this data lies entirely with the user. Although these data have been processed successfully on computers of WRD, no warranty, expressed or implied, is made by WRD regarding the use of these data on any other system, nor does the fact of distribution constitute or imply any such warranty. In no event shall the WRD have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of the delivery, installation, operation, or support by WRD. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ARCE Full coverage zipped 0.194 http://water.usgs.gov/GIS/dsdl/sim06-2949A_dar_bth_cont.e00.gz None. This dataset is provided by USGS as a public service. 20070126 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing address

445 National Center

Reston VA 20192 USA 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+sim06-2949A_dar_bth_cont FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998 local time None None