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3. Flooding and Hydrology: <br /> Approximately 33 million acre-feet of water flows <br /> into the Delta yearly producing a complex network <br /> of waterways and marsh. Within the Delta there <br /> are approximately 700 miles of slow moving, navi- <br /> gable waterways that rise and fall with the tides <br /> and gradually become more saline as they approach <br /> the Bay. Most of these waterways were naturally <br /> created although many have been straightened or <br /> reinforced through man' s actions. A few have been <br /> dredged for shipping. <br /> The saline gradient fluctuates from year to year <br /> and even season to season. Its position is established <br /> by the amount of inflow from rivers and streams. In <br /> a normal year of precipitation the saline waters will <br /> not intrude into the San Joaquin Delta. However, <br /> in 1931, Turner Cut was subject to salt water intru- <br /> sion (See Map 2) . <br /> The greatest hazard in the Delta is flooding. Much <br /> of the Delta is subject to 100 year floods including <br /> Lower Roberts Island; flooding is highly dependent <br /> on the quality of the levees. Like many of the Delta <br /> islands, Lower Roberts island is gradually subsiding, <br /> producing a greater strain on the levees. The latest <br /> topographic map from the State Department of Water <br /> Resources indicates that the site for the proposed <br /> marina is, on the average, 10 feet below sea level. <br /> While no levee failures have been recorded on Lower <br /> Roberts Island, such occurrences are not unprecedented. <br /> In the past 75 years, more than 100 islands and tracts <br /> have been flooded because of levee failures. (See Map 3) . <br /> 4. Climate : <br /> The Delta climate is characterized as Mediterranean <br /> with warm rainless summers and cool moist winters. <br /> During the winter months the inner Delta bound by <br /> waterways, becomes fog prone. Delta fog is extremely <br /> dense and moves in quickly. Boat and car travel <br /> becomes extremely hazardous in the Delta during <br /> winter months. During the spring and summer Delta <br /> weather is characterized by gusty winds caused by <br /> the pressure differential between hot air over the <br /> interior valley region and cool heavier air over <br /> the ocean. <br /> 5 - <br />