*2.3. Early Development Conditions*

The pre-development landscape has been radically modified over two centuries, starting in the mid-18th century when Spanish settlers arrived, bringing livestock and range management. The discovery of gold along the American River in 1848 spurred agricultural and urban development in the Central Valley. That same year, the federal government transferred ownership of "swamp and overflowed lands" to California on the condition that they be drained and reclaimed. These permanent wetlands were largely converted to agriculture by 1930.

Regular flooding on major rivers led to the formation of levees and reclamation districts by 1860. Starting in the 1870s, studies were conducted to determine how to reduce flooding and supply irrigation water. The Office of the State Engineer was established in 1878 to further these plans, and in 1880 the legislature approved the Drainage Act, proposing valley-wide flood control. These studies culminated in the Central Valley Project Act in 1933. Water resources were further reconfigured in response to voter approval of the Burns-Porter Act in 1960, financing the State Water Project [64]. Ultimately, the Central Valley was re-plumbed to move water throughout the state in a complex man-made water system with some 1300 miles of aqueduct and 1350 surface reservoirs with 40 million acre-feet (32.4 BCM) of storage [64].

Although this period of early development between WYs 1851 and 1911 is poorly understood hydrologically, limited availability of instrumented data facilitated previous work. Arguably the most significant data set compiled during the latter part of this period was published by the California Department of Public Works [65], the predecessor to CDWR. This document, commonly referred to as Bulletin 5, reports a long-term record of stream flows to the Central Valley beginning in WY 1872.

Moftakhari et al. [66] reconstructed a Delta outflow time series spanning the early development period (beginning in 1858) through correlation with tide gauge data measured at San Francisco. Moftakhari et al. [67] reconstructed a Delta outflow time series beginning in WY 1850 through correlation with Sacramento River stage data measured at Sacramento. River stage data were unavailable over WYs 1863–1881; thus, the authors augmented the reconstructed outflow time series using the work of Moftakhari et al. [66]. MacVean et al. [68] explored the hydrology of the early development period following 1850 by synthesizing reconstructed time series of precipitation, basin inflows, land use, and levee construction in a semi-distributed hydrologic model. They concluded that, in spite of significant anthropogenic modifications to the region's hydrology, by the 1920s Delta outflow remained similar to pre-development conditions, due in part to flow augmentation provided by flood control infrastructure and enhanced channel conveyance. MacVean et al. [68] concluded that levee construction, rather than land use change, had the greatest impact on Delta hydrology during this early development period.
