DOI: 10.5061/dryad.cvdncjt8k
title: Impact of dam height and grain size distribution on breaching of non-cohesive dams due to overtopping

description: The National Inventory of Dams reports 74,400 earthen dams in the United
 States in 2021; of these dams, approximately 27% are considered at high or
 significant hazard risk, that is dam failure will cause widespread damage
 and loss of lives. The most frequent cause of dam failure is breaching
 caused by overtopping. Accurate predictions of breach evolution are thus
 crucial to determine flood hydrographs for the safety of communities and
 properties at risk. Laboratory experiments were conducted on non-cohesive,
 compacted embankments to understand the role of dam height and sediment
 grain size on breaching caused by overtopping. Dam heights varied from 10
 cm to 45 cm. Model structures were built with fine sand or with a mixture
 of fine sand and silt. Experiments showed that increasing dam height
 increases peak discharge. The presence of silt in model embankment
 material, on the contrary, lowers peak discharge and makes failure longer.
 In sand dams, sediment deposition on the downstream face becomes important
 as dam height increases. This deposition reduces incision rate of the
 breach channel, delaying time to peak and rapid channel widening. In all
 embankments, breach evolution was gradual until erosion of the breach
 channel reached the reservoir. Throughout the experiment, bank failure
 caused gradual widening of the breach channel. In presence of silt, no
 sediment deposition occurred on the downstream face, and time to peak
 increased with dam height because upstream migrating erosional waves
 formed in the breach channel, and the time for these waves to reach the
 reservoir increased with dam height. Breach channel widening associated
 with bank failure is practically non-existent until peak discharge is
 reached, then sudden widening caused by major failures occurs. Overall,
 breach width decreases with an increase in silt content.
description: Breach hydrographs The breach hydrographs
 were collected using sonar probes and a point gauge to measure the
 elevation of the upstream reservoir. An upstream weir was used to control
 the reservoir head and direct excess flow away from the dam. The head of
 water over the weir and known inflow discharge were used to compute the
 weir discharge. Conservation equations were then used to compute the
 discharge through the channel. The data had then been smoothed and poor
 data eliminated.  Channel width
 Two cameras monitored spatial and temporal changes in breach
 width. One camera was placed downstream of the dam to image the downstream
 dam face and a GoPro camera was placed just upstream of the dam to image
 the dam crest. Frames were extracted from the video recordings and
 manually digitized the dam geometry throughout the experiment. This
 digitized data could then be processed into temporal width data at varying
 locations along the downstream dam face and crest.
 Channel depth/incision: Breach erosion on
 dam crest was measured 10 cm upstream of the downstream edge of the crest
 with a Keyence laser profiler LJ-V7200. The laser emits a beam to the dam
 crest and receives the reflected light. Based on the change in the
 position where the light is received back into the laser, the sensor can
 detect the change in the distance to the dam crest. A MATLAB code was
 developed and used to convert laser outputs into temporal data for
 elevation on the dam crest as well as smooth the data. 
description: Microsoft Excel to open all data.