HYDROLOGY OF SOME TIDAL CHANNELS IN ESTUARINE MARSHLAND NEAR SAN-FRANCISCO

Measurements of velocity, depth, discharge, and slope were simultaneou sly made at ten gages along a natural estuarine channel 19,000 feet in length in Petaluma Marsh, California. Along the study reach the chann el decreases from a width of 47 feet at its mouth to nearly zero at it s headward extent, with accompanying decrease in depth. Though gage he ight varies with time in a smooth sinusoidal manner at all stations, t his is not true for velocity, discharge, or slope. Velocity is rather constant for long periods in the ebb cycle and differs but little alon g the length of the channel. It is somewhat higher on ebb than on floo d tide. At most gage sites, velocity continues one-half to one hour af ter the gage height has reached its maximum or minimum value and rever sed. In this channel water surface slope is considerably greater in th e midreach of channel than in either the mouthward or headward reaches . Slopes vary from less than .0001 to about .0005 through much of a ti dal cycle. At some stages of both ebb and flood, the upper end of the channel has a positive slope while the lower end a negative or adverse slope. At those times the longitudinal profile of water surface is bo w shaped or V shaped.