NAUTICAL CHART MANUAL - VOLUME 1 - POLICIES AND PROCEDURES Seventh (1992) Edition CHAPTER 4 - HYDROGRAPHY U.S. Department of Commerce Office of Coast Survey UNITED STATES DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration NATIONAL OCEAN SERVICE Office of Coast Survey Silver Spring, Maryland 20910-3282 SEPTEMBER 22, 2000 MEMORANDUM FOR: All Cartographers Marine Chart Division FROM: Fannie B. Powers Chief, Quality Assurance, Plans and Standards Branch SUBJECT: Chapter 4 Effective immediately, the attachment replaces Chapter 4 in the Nautical Chart Manual, Volume 1, Part 1, Seventh (1992) Edition in its entirety. Chapter 4 is revised as follows: 1. Outdated procedures are deleted. 2. Acronyms are revised. 3. Pages are renumbered. 4. The ENC Object, Dredged Area, is updated a follows: A. Correctly identifies those shoaling areas (within a dredged area) which contain soundings and depth contours as depth areas. B. Explains which MCD channels should actually be collected as Fairways. C. Includes a Table of Contents and an Example Index. D. Changes the page numbering system of the Dredged Area NOS/ENC Objet Specifications. 5. Cartographic Orders and Memorandums are embedded in the text. The following Cartographic Orders were not previously distributed, but are now embedded in Chapter 4. A. Cartographic Order 026/00, filed in Section 4.4: Subject: (1) Updating of Nautical Chart Manual Information on Depth Curves; (2) Nautical Chart Manual Incorporation of ENC Objects: Depth Contour and Depth Area; (3) Depth Area NOS/ENC Object Specifications Pages The Nautical Chart Manual, Volume 1, Part 1, Seventh (1992) Edition, pages 4-41 to 4-61 are revised and the ENC Object Specifications’ section pages 4-i, 4-ii and 4-DA1 to 4-DA94 are added to Chapter 4. Updated information on depth curves and depth contours is added to the Nautical Chart Manual. Information is embedded about the ENC objects Depth Contour and Depth Area. Chapter 4 includes the corresponding NOS/ENC Object Specifications pages for the Depth Area ENC object. The NOS/ENC Object Specifications pages for the Depth Contour ENC object will be provided as an attachment in a separate cartographic order. Please note the new name and numbering system of the specifications (ENC), “ENC Extraction Specification” is now entitled “NOS/ENC Object Specifications”. The new numbering system will now incorporate two (2) lettrs from each ENC object name. B. Cartographic Order 031/00, filed in Section 4.2.4: Subject: Danger to Navigation Reports NOS field units (vessels, contractors and navigation response teams) are required to submit a Danger to Navigation Report upon discovery of any of a variety of dangers listed in Section 4.2.4. Historically, these dangers have been reported directly from the field unit to the U.S. Coast Guard (USCG) and the National Imagery and Mapping Agency (NIMA) for inclusion in the Notice to Mariners (NM). This policy has changed and Danger to Navigation Reports shall now be processed according to the procedure detailed in Section 4.2.4. Danger to Navigation Reports shall be evaluated for chart application in the Marine Chart Division. MCD shall submit information evaluated and applied from the Danger to Navigation Reports to the USCG and NIMA for inclusion in the NM. It should be noted that the attachment requires that Danger to Navigation Reports must be processed immediately and NM items generated from a Danger to Navigation Report should be submitted to USCG and NIMA within one week, at most, after receiving the document in MCD. C. Cartographic Order 032/00, filed in Section 4.13.5: Subject: Platform Sign Designations The Eighth Coast Guard District has discontinued publishing new and revised platform sign designations Effectively immediately, within the area of the Eighth Coast Guard District’s jurisdiction, sign designations shall be removed from charts going forward for printing. The positions of platforms and other oil/gas structures will continue to be charted and updated. Sign designations shall be charted for platforms that fall within the areas of all other Coast Guard Districts. NAUTICAL CHART MANUAL 4 HYDROGRAPHY 4.1 General Natural hydrographic features are charted after a thorough study of the configuration of the bottom as portrayed by surveys, primarily NOS hydrographic surveys. Submarine relief must be presented clearly, and important objects must not be obscured by other data. A dangerous rock, an islet, or the least depth over a shoal must be shown prominently; small islets and rocks should be exaggerated, if necessary, to make them easily discernible. The graphic portrayal of hydrographic information on a chart is represented by depth soundings, their associated depth contours or curves, depth-dependent color designations (blue tints), and notes showing the controlling depth of improved channels. Together these must convey adequate depth information to enable the chart user to navigate safely. Labels describing the character of the bottom are particularly important in harbors and other anchorage areas, but are also useful to fishermen. Symbols and labels depicting the existence of such natural dangers as ledges and reefs and isolated rocks, as well as man-made obstructions ranging from fish havens to cribs and platforms to submarine cables and pipelines, are also charted. Guidelines published in the Hydrographic Manual, Fourth Edition, 1976, and Wire-Drag Manual, Publication 20-1, are designed to ensure that basic NOS hydrographic surveys (as defined in Section 4.2.1) supersede all previous NOS surveys in the area covered. The proper charting instructions must be clearly stated, and exceptions shall be noted in the Descriptive Report (DR), for the application or removal from charts of wrecks, dangers, least depths, or wire-drag clearances, etc. Data handling throughout the system must be prompt and thorough to ensure timely dissemination of information to chart users. Questionable recommendations for charting action must be referred for resolution to HSD through the Chief, NDB. When applying hydrography, the cartographers must constantly be alert for items that should be included in the NM. This is most important since failure to recognize a potential navigational hazard and to alert mariners via the NM could result in a major marine disaster. Additionally, early requests for supplemental information to facilitate the processing of these items is critical. NDB shall be notified immediately of any requirement for data to rectify discrepancies and deficiencies which may preclude safe disposition of critical items or eventual assimilation of the source into the data base. Items requiring immediate attention for charting action or publication in the NM should be applied and a NM issued pending such resolution. The mariner must always be informed of any dangers suspected, whereas final corrective action can be taken later. A questionable feature is usually charted as "Rep" (reported) until it has been resolved. When applying reviewed basic surveys to the charts, the cartographer must also take care not to inadvertently remove items dating from sources more recent than the survey. Conflicts between REVISED AUGUST 25, 2000 Section 4.1 NAUTICAL CHART MANUAL contemporary hydrographic and topographic surveys in the delineation of the low water line, or the height rocks awash actually uncover, should be resolved by giving greater weight to the information on the reviewed hydrographic survey. More care is required in evaluating unreviewed hydrographic surveys because of the development of increasingly sophisticated photogrammetric methods (e.g., infrared photography and photobathymetry) to record these hydrographic details. Hydrography shall be applied from the largest- to the smallest-scale charts, with the larger-scale portrayal serving as the source for the next-smaller scale. Detail is eliminated and generalized as scale is reduced. Yet critical shoal soundings, rocks, and other dangers must be retained when applying surveys through the scales. Significant submerged features should not be generalized, and generalization must never compromise navigational safety. To aid in navigating by echo-sounding apparatus, depth curves are given special prominence on nautical charts in areas where modern hydrographic surveys have been made. The more accurately the chart depicts deepwater submarine relief, the more certain the navigator can be of the vessel's position. Note that hydrographic features are always labeled using slant (italic) type whereas topographic features are labeled with vertical type. 4.2 Hydrographic Surveys The principal objective of hydrographic surveys conducted by NOS, with few exceptions, is to obtain basic data for the compilation of nautical charts. Emphasis is on those features that may affect safe navigation. The accuracy and adequacy of a nautical chart depend on the quality of the hydrographic surveys from which it is compiled and the skill of the cartographer in applying this information. Generally, only basic surveys and field examinations are assigned "H" or "FE" registry numbers and are archived. However, upon occasion, special-purpose hydrographic, reconnaissance, or evaluation/test surveys are assigned a "D" registry number in conformance with requirements set forth in the project instructions developed for that survey. A "D"-numbered survey may be assigned a Chart Letter or Blueprint designation for storage and retrieval. The Office of Marine and Aviation Operations (OMAO) is responsible for the management