Legal Alstead – Culvert Assessment

Legal | Failed Culvert and Embankment Evaluation

Why GeoInsight

We were retained as an expert witness to evaluate the failure of the culvert and embankment located on Cooper Hill Road, which connects Routes 12A and 123, in Alstead, New Hampshire. The embankment failed rapidly due to a large backup of water during the October 2005 prolonged precipitation events that resulted in a catastrophic loss of life and damage to downstream structures.

Achievements

CULVERT AND EMBANKMENT FAILURE: WATERSHED DRAINAGE ANALYSIS – To provide expert support services for the matter, we interviewed Town of Alstead personnel and reviewed numerous accounts of the failure to gain an understanding of conditions at the time of the failure. A hydraulic analysis was then conducted to assess the likely volume and flow rate of water being discharged by the watershed upstream of the culvert so that we could calculate the theoretical volume of water retained by the embankment, which was never intended to hold back water.

CULVERT DESIGN EVALUATION AND FORENSIC ASSESSMENT Using various engineering tools, and including hydraulic modeling and slope stability software, we developed a conceptual re-creation of the failure of the culvert and embankment. This required estimating the previously existing dimensions of the embankment based upon photographic evidence and field measurements and considering significant variables associated with the evaluation including blockage of the culvert by debris, variable rates of flow, and the rate that water was being impounded behind the embankment. The analysis demonstrated that the embankment was not physically stable with water dammed up behind it. We prepared an expert opinion regarding the characteristics of the conditions leading to the failure of the culvert and embankment, and the associated nature of the ensuing floodwater energy.

Client: Legal
Location: Alstead, NH
Services: Expert Services
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Scope of Services

  • Engineering Assessment
  • Culvert and Embankment Failure
  • Expert Witness Testimony
  • Litigation Support
  • Forensic Assessment