vary  slightly  depending  on  bottom  topography.  Thus, mean  in  order  to  conduct  a  proper  surf  observation, with 6-foot breakers, the breaker line is located where commonly  called  a  SUROB.  See  figure  4-1.  The the depth to the bottom is about 8 feet. following factors greatly influence surf: SURF  ZONE  HYDROGRAPHY Besides the winds and seas, the hydrography of a beach has a major impact on the character of surf. The hydrography  in  a  surf  zone  includes  the  water  depth, nearshore  currents,  tides,  the  shoreline  configuration, the beach slope (gradient), and bottom composition. In fact,  the  beach  slope  is  the  most  important  factor  in determining  the  type  of  breaker  most  likely  to  be present.   Due   to   dissipation   over   distance,   waves breaking closer to shore will do so with less energy and lower  heights  than  waves  breaking  farther  offshore. Bottom  features,  such  as  ridges,  canyons,  sandbars,  and troughs,  can  greatly  affect  where  waves  break.  It  is important  to  remember  that  ridges  and  sandbars  will cause  waves  to  break  farther  from  shore  and  with stronger   force.   When   waves   are   observed   that consistently break in the same area from one day to the next, there is probably a submerged feature such as a sandbar or reef in the surf zone. Beach  orientation  or  beach  face—the    true direction  a  person  standing  on  the  beach  and looking out to sea would face, Beach slope—the  ratio  of  the  drop  in  bottom depth   compared   to   the   horizontal   distance traveled in the surf zone (rise over run). Usually obtained   by   seal   team   surveys   or   from hydrographic charts. DESCRIPTIVE  TERM SLOPE  (every  1  unit  of rise  per  unit  of  beach length) Steep Greater  than  1:15 Moderate 1:15  to  1:30 G e n t l e 1:30  to  1:60 Flat Less than 1:120 Knowledge  of  beach  hydrography  is  essential  to producing   accurate   surf   forecasts.   There   are   many sources of hydrographic data, including climatological charts   and   tables,   intelligence   reports,   seal   team reconnaissance   reports,   as   well   as   high   resolution shallow  water  satellite  imagery.  Keep  in  mind  that sandbars and other bottom features shift with the tides and  seasons.  Therefore,  the  more  recent  any  beach survey information is, the more accurate and useful it will be. Coastal   zone   topography—the    presence    of islands  or  other  wave-blocking,  offshore  land masses  that  affect  wave  refraction  (bending  of wave trains). Near-shore and offshore bottom hydrography— the  presence  of  underwater  sandbars,  ravines, reefs,  or  other  features  on  the  ocean  bottom. Coral and rocks can cause hazards to personnel and equipment. DESCRIPTIVE  TERMS  RELATING  TO SURF  OBSERVATIONS Many terms used to conduct a surf observation are unique  to  either  the  observation  or  to  an  amphibious assault.    Every observer must know what these terms Sandbars—formed     as     a     result     of     sand transported by waves and currents. Unlike reefs, these are transitory in nature and change with the seasons and tides. They may be exposed during low tide and cause landing craft to become stuck. In addition, the volume of water carried over the bar  must  return  seaward.  The  return  flow  may Figure 4-1.—Nearshore profile. 4-2