Why Is Sediment Removal So Expensive?

The economic viability of expanding an existing reservoir versus building a new reservoir seems outrageously huge.  The information below is from the excellent California WaterBlog.  Storage should be a consideration when looking at the matrix of water resource management strategies.  I wonder if this is applicable to Texas and what construction, project delivery, technology, permitting, sediment reuse forces are on the horizon that might disruptive the economic gap?  You have a cost factor of between 8 and 10 that needs overcoming - which seems a huge challenge, but potentially a huge opportunity.

"Removing sediment from reservoirs is often suggested as a potentially better way to expand storage capacity than raising dam heights or building new reservoirs. This is a natural notion to explore given the cost and likely environmental impacts of traditional expansions.

For perspective, the construction cost of conventional reservoir expansion is about $1,700 to $2,700 an acre-foot (af) of storage capacity. For example:

• Expanding Shasta Reservoir at $1,700/af: $1.1 billion for 634,000 af of new capacity
• Building Sites Reservoir (Colusa County) at $1,800/af: $2.3 billion to $3.2 billion for 1.3 million to 1 .8 million af of new capacity
• Building Temperance Flat Reservoir (upper San Joaquin River) at $1,900/af: $2.5 billion for 1.3 maf of new capacity
• Expanding Los Vaqueros Reservoir at $2,000/af: $120 million for 60,000 acre-ft of new capacity
• Expanding San Luis Reservoir at $2,700/af: $360 million for 130,000 acre-ft of new capacity

The cost of expanding reservoir capacity by removing sediment seems likely to be $5 to $20 a cubic yard or $8,000 to $32,000/af (at 1,600 cubic yards/acre-ft)."