{"nrhp_refnum":"77000184","name":"Great Stone Dam","other_names":["Essex Company Dam"],"category":"structure","location":{"address":"Merrimack River & MA 28","address_restricted":false,"city":"Lawrence","county":"Essex County","state":"MA","lat":42.700967913000056,"lon":-71.16611900099997,"geom_source":"nps_gis"},"listed_date":"1977-04-13","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering"],"significance_levels":["state"],"summary":{"what_it_is":"A granite and rubble overflow dam across the Merrimack River in Lawrence, Essex County, Massachusetts, just west of the Route 28 crossing. It was built 1845-1848 for the Essex Company and designed by Charles S. Storrow.","why_significant":"The nomination calls it the first weir to cross a large American river with a height over ten feet. It embodies the weir design principles of the early nineteenth century and remained virtually unchanged from 1848. It also served as a model for later dam builders.","narrative":"Spanning the Merrimack River at Lawrence, Massachusetts, this granite dam was built between 1845 and 1848 to hold back the river and raise the water level enough to power mills through two canals. It is 900 feet long in its overflow section, with wing walls bringing the total to 1,629 feet, and stands thirty to forty feet high. Charles S. Storrow, the Essex Company's treasurer and chief engineer, designed it, and Charles Bigelow oversaw construction. The dam is described as the first weir across a large American river to exceed ten feet in height. Its skewed, slightly curved form, ice-shedding crest, earthen embankment and tested hydraulic cement reflect early nineteenth-century practice. Engineers such as James Francis modeled later dams on it. It has withstood floods, including the 1936 freshet, without repair for about 130 years. Only a concrete fishway from 1918 and added crest dowels around 1914 changed it.","period_of_significance":"1845-48","architect_builder":"Charles S. Storrow (designer); Charles Bigelow, Construction Engineer of the Essex Company","architectural_style":null,"criteria":[],"status_note":"Dam remains in place with its original form largely unaltered; a concrete fishway added in 1918 is still in use and crest stones were reinforced around 1914.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:11:53.593214-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/27/7950/63795027/content/electronic-records/rg-079/NPS_MA/77000184.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/77000184/c7b9303bba-800.webp","url_1600":"https://nationalhistoricalregister.com/media/77000184/c7b9303bba-1600.webp","licence":"CC BY 3.0","author":"John Phelan","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Great_Stone_Dam_on_the_Merrimack_River,_Lawrence_MA.jpg\" rel=\"noopener\">John Phelan</a>, <a href=\"https://creativecommons.org/licenses/by/3.0\" rel=\"license noopener\">CC BY 3.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Great_Stone_Dam_on_the_Merrimack_River,_Lawrence_MA.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/63795027","wikipedia":"https://en.wikipedia.org/wiki/Great_Stone_Dam","wikidata":"https://www.wikidata.org/wiki/Q5600041"},"indexable":true,"url":"https://nationalhistoricalregister.com/massachusetts/essex-county/great-stone-dam-77000184/"}