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Both blocks were tetrahedral (4-sided), which is the most basic non-cubic block geometry but also the most likely removable block geometry from a rock mass [17]. The blocks were located close to the spillway gates where flow could still be relatively characterized as 2D channel flow, before becoming more complex further downstream. This was done to facilitate comparison with physical hydraulic model testing done on 3D tetrahedral blocks in a flume channel as another facet of this research study. The blocks were fabricated out of concrete and instrumented with pressure and displacement sensors on each of the block faces (Fig. 4). This was done to allow measurement of hydrodynamic forces applied to the block during spill events and track block movements precursory to removal. Sensor cables were run through waterproof conduit to a datalogger located above the spillway crest. Measurements were captured at a frequency of 100 Hz to obtain high resolution data sets for hydrodynamic pressure and displacement. Fig. 4 Artificial rock blocks, as constructed. Note displacement sensors are on block faces within the rock mass and subsequently not shown [16]. 3. MARCH 2016 SPILL EVENT Block 1 was installed in November 2012, while the Block 2 was installed the following year in November 2013. Subsequent drought conditions in California, however, lead to no significant spill events that impacted the blocks. It wasn’t until March 2016, when a peak discharge of 126 m3/s resulted in the removal of Block 2 from below the low-level spillway gates. During the afternoon of March 5, 2016 discharge from the spillway began through the low-level outlet gates and at approximately midnight flow through the upper-level gates commenced. The peak discharge occurred around 6 am the following morning. Flow through the upper- level gates terminated on the morning of March 7 around 5 am, while flow 1495