There's no "Economy of Scale"

The creek that runs through our property changed course a couple weeks ago after a short rainstorm. The creek bed is in a deep ravine and drops 100' over about 1100 feet. Usually there's just a trickle of water in it, and in a typical rainstorm it gets to be about ankle deep. A couple weeks ago, it must have gotten dammed up for a while by a log, which finally gave way and sent a lot of water down the creek at once. The water scrubbed out the creek bed and ended up rerouting the creek by cutting a trench through what people in this area call a "hogback", which is a narrow ridge that extends out from a hill down to a river or creek. The creek only has to erode about 10' deeper until it hits sandstone. (I wonder if we'll still be alive to witness that.)

Over the course of years creeks and rivers wander all over as they erode new paths and silt up old ones. When there is man made infrastructure nearby, people will build walls and erosion control structures (like piles of rocks) to forestall the encroachment of water. In more extreme cases, people build dams and reroute rivers for cities' water supplies. 

When you divide the big costs of big infrastructure projects over many people and compare the cost to install a huge pipe versus a bunch of small ones, or one giant dam versus a bunch of individual's flood control measures you can say there is an "economy of scale". Of course there's an inverse massive loss of a resource, (e.g. California Water Wars) and "perpetual" maintenance cost to maintain some structure or system that's fighting nature everyday over a huge area and a wide range of conditions that can't ever be anticipated by engineers.

The "need" for flood control or similar civil engineering projects stems from how people own land in the United States. We generally own a chunk of land that's defined by a survey and ultimately related to its position on the globe, rather than a right to a use of land in some region. (in some cases, property rights are actually deliniated along resource use lines rather than geographical lines). And it seems lilke such property rights are really tied to the concept of work making the land more organized and valuable, e.g. building a barn or a house.