Occasional large floods do hit the area, so the dam is designed to survive overtoppings and also has a pair of seven-gated spillways capable of handling more than 45,000 cubic feet per second (1,300 m3/s).

Conversely, in the summer, most of the smaller streams dry up and the larger waterways are reduced to trickles, leading to equally dangerous droughts.

The bedrock of the region has notably low permeability, leaving little groundwater available (particularly when compared to nearby Los Angeles and Orange Counties).

[4] Here the river after departing a broad valley cuts through a steep and narrow gorge, providing an ideal site for a reservoir.

During the early stages of construction the Sweetwater River was diverted underneath the foundation structure into a square masonry culvert 30 inches (76 cm) in diameter.

The tunnel provided sufficient discharge capacity for the river past the dam site, as 1886–1887 were below average precipitation years.

[8] As construction progressed, the original thin arch design was considered both unstable and inadequate for the county's growing water needs.

[4][9] The stone used in the dam's construction was quarried from a large rock outcropping about 800 feet (240 m) downstream on the south bank of the river.

[15] In the winter of 1895, heavy rains caused the Sweetwater River to rise to record levels, and the dam's outlets and spillways were unable to handle the excess inflow of water.

[4] In the winter of 1915, southern California was experiencing a devastating drought that had drained area reservoirs to record low levels over more than three consecutive years, causing massive agricultural and ranching losses.

Hatfield's venture was apparently a success, but it is not known what actually caused the massive floods that tore through the county beginning December 9, the day after he started his ill-fated scheme.

Flooding deposited so much sediment that the southern end of San Diego Bay was filled with it – much of the sand remains today in the form of shoals that must be periodically dredged to accommodate boat traffic.

[17][18][19] The Sweetwater River rose until it reached a peak flow of 45,500 cubic feet per second (1,290 m3/s) on January 30, 1916 and though the dam had been increased in height and its spillway capacity enlarged, this did little to prevent it from overflowing.

The failure of the dam caused extensive damage downstream, including the destruction of over 15,000 ft (4,572 m) of Sweetwater Water Co. pipeline, all railway track and electric utility lines.