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Laguna Lake Development Authority Lake Elevation |
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The hydrology of the lake has a natural stage regime which in the dry season results in a minimum lake elevation of about 10.5m. controlled by mean level in Manila Bay. At the end of the dry season, the lake level may drop below the level of high tide in Manila Bay, resulting in the intrusion of seawater up the Pasig river. With this diurnal reversal, the highly polluted waters of the Pasig river system are carried in the lake. The tidal influx is also the primary cause of elevated salinity in the lake during this part of the year (Francisco, 1985).
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During the wet season, precipitation results in an annual mean high water elevation of 12.5m and a peak elevation which may reach as high as 14.6m for a 100 year recurrence interval. During extremely wet years, widespread flood damage occurs along the lakeshores because the land is relatively flat for several kilometers inland in most areas. Also during this period, the Marikina river floods the Pasig river and overflows into the Laguna de Bay via the Napindan Channel because the Marikina river can generate flood-flows of about 200 m3s to 4000 m3s, and because the Pasig river bank full channel capacity varies from as little as 50 m3 to only about 750 m3s. Depending upon the tide and local inflow, the Marikina river causes flooding in and around Metropolitan Manila. |
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