2021-11-22-minutes-public-works-study-session

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NAD 83 and NAVD 88, although still the official horizontal and vertical datums of the National Spatial Reference System (NSRS), have been identified as having shortcomings that are best addressed through defining new horizontal and vertical datums. Specifically: NAD 83 is non -geocentric by about 2.2 meters. NAVD 88 is both biased (by about one-half meter) and tilted (about 1 meter coast to coast) relative to the best global geoid models available today. These issues derive from the fact that both datums were defined primarily using terrestrial surveying techniques at passive geodetic survey marks. This network of survey marks deteriorates over time (both through unchecked physical movement and simple removal), and resources are not available to maintain them. It is likely that existing County vertical data could be as much one-half of one foot off from Vantage to Snoqualmie Pass. In late 2020, the NGS solicited surveyors across the county for support of the spatial shift imitative. Kittitas County built the 2021 survey work program supporting the request (EXHIBIT 1 — map detailing the monuments updated). A current state map depicting other county and state efforts is attached as EXHIBIT 2. DISCUSSION: PW has done a good job getting the County ready for the national shift in reference frames. Once NGS completes this national effort, the amount of data upload and associated GIS layer work is expected to be significant. The potential benefits to the County's tax parcel layer appear equally significant. Once the NGS reference frame shift is complete, PW recommends evaluating the impacts to the County's tax parcel database and incorporating refined monumentation data provided by PW the past several years. Current NGS efforts will improve State Plane coordinates in the County adding additional accuracy to the network supporting eventual improvements to the County's tax parcel layer. FISCAL IMPACTS: Undetermined at this time. ATTACHMENTS: Exhibit 1: Kittitas County Monument Map Exhibit 2: WA State Map Page 2 of 4 Public Works "Work Session Staff Report", 2021