The natural annual discharge of the San Joaquin before agricultural development is believed to have been between 6–7.9 million acre feet (7.4–9.7 million dam3), equaling a flow of roughly . Some early estimates even range as high as 14 million acre-feet (17.3 million dam3), or more than . The numerous tributaries of the San Joaquin – the Fresno, Chowchilla, Merced, Tuolumne, Mariposa Creek, Calaveras, Mokelumne, and others – flowed freely across alluvial flood plains to join the river. All of the major tributaries of the river originate in the Sierra Nevada; most of the streams that start in the Coast Range are intermittent, and contribute little to the flow of the San Joaquin. During the winter, spring, and early summer, storms and snowmelt swell the river; in 1914 – before the development of major dams and irrigation diversions – the California Department of Engineering estimated the river's flow in full flood at . In late summer and autumn, there is little water left over to replenish stream flow. Historically, groundwater seepage from Tulare Lake maintained a significant base flow in the river during the dry months – some accounts suggest over 50 percent.