LITTORAL ENVIRONMENT OBSERVATION (LEO) DATA SUMMARIES, 

 NORTHERN CALIFORNIA, 1968-78 



by 

 Christine Schneider and J. Richard Weggel 



I. INTRODUCTION 



A major problem confronting coastal project planners and designers is the 

 lack of data on waves and currents acting in the nearshore zone. Data obtained 

 by recording instruments are expensive and appear to be rarely available at the 

 precise locations under study. Also, since nearshore wave modifications are 

 complex and highly variable over short distances, data that are transposed from 

 one site to an adjacent one may not be reliable. Simple estimates of the direc- 

 tion from which waves approach the coast are also not generally available because 

 wave gages are usually located seaward of the breakers. Wave direction is an 

 important variable in determining the rate and direction of longshore sand trans- 

 port, and one measurement that is easily estimated from visual observations. 



The Littoral Environment Observation (LEO) Program was established to help 

 overcome some of these problems by providing estimates of coastal phenomena at 

 low cost. Under this program, volunteer observers are recruited to make daily 

 estimates of variables such as breaker height, wave period, direction of wave 

 approach, wind speed and direction, longshore current velocity, and beach slope. 

 Other parameters estimated are the spacing between beach cusps and between rip 

 currents when present. At some LEO sites, monthly sand samples are collected 

 from the swash zone. Observers use simple, inexpensive equipment to obtain the 

 data and, for some variables like wave height and direction, simply record a 

 visual estimate of the variable. Because of the simple data collection proce- 

 dures used, any individual observation may be of questionable accuracy, but 

 statistical descriptions of the variables can provide insight into the local 

 littoral environment. Also, LEO observations in a continuous series over time 

 can be extremely useful in describing the physical coastal environment at a 

 site. Observer bias that may exist for some sites can be partially compensated 

 for by determining relative changes rather than absolute values of certain 

 variables. 



LEO data may be used to estimate longshore sand transport resulting from 

 waves breaking at an angle to the shoreline. These waves produce longshore 

 currents which may transport large quantities of sand along the shore. An em- 

 pirical equation that relates longshore sand transport with wave conditions 

 recorded under the LEO program is given in Chapter 4 of the Shore Protection 

 Manual (SPM) (U.S. Army, Corps of Engineers, Coastal Engineering Research 

 Center, 1977). Some recent theoretical developments allow the computation of 

 sand transport rates using longshore current velocities (see Walton, 1980), 

 which are also available through the LEO observation program. Therefore, LEO 

 provides two separate (although not completely independent) methods of deter- 

 mining longshore transport rates. More details regarding LEO data collection 

 procedures are available in Schneider (1981), and information on the comparison 

 of LEO wave height and period data with data obtained from wave gages is avail- 

 able in Schneider and Weggel (1980) . 



This report presents data obtained at 25 LEO sites in northern California 

 starting with inception of the program in 1968 and continuing through 1978. 



