At the listed coordinates, you are standing in a floodplain of the San Joaquin River.
WHAT IS A FLOODPLAIN?
A floodplain is the part of the land where water collects, pools, and flows during the course of natural high-water events. Fresno County is located in a historic natural floodplain. When a part of land is "in the floodplain," this is accepted to mean that the land is within reach and not protected from a "100-year flood" event. The protection that levees, dikes, and other flood control infastructure provide is limited, and only serves useful for smaller scale floods. The way they work is that these protection barriers cause high water to keep flowing past the land instead of spreading out further into the surrounding areas, reducing flooding. Properties or lands in the floodplain may have levees for limited protection, or they can have no protection whatsoever, just right on the banks of the river/water source. Both are considered to be in the floodplain if they would not withstand a 100-year flood event.
WHAT IS A 100-YEAR FLOOD EVENT?
A “100-year flood event” is fairly large, historically infrequent flood. The reason for the name "100-year" is that a flood of the large, projected size is estimated to only have a 1% chance of happening again the next year. This means if nothing changed, in 100 years it would have a 100% of happening again, and therefore the catastrophic flood would happen once every 100 years. However, we know this is not how it always plays out, as Nature and the Forces at work are not routine, and rarely repeat themselves in the same fashion. There is no way to predict when the next flood will occur. There could be several 100-year floods in a short period of time, or the area might not see another 100-year flood in our lifetimes or our grandkids’ lifetimes.
HOW ARE FLOODPLAINS FORMED?
Meandering rivers, such as the San Joaquin, erode sideways as they travel downstream (as taught in this earthcache. The river, when overflowed, leaves behind (deposits) layers of alluvium. It builds up to create the flat floor of the floodplain. This floodplain will contain sediments such as sand, gravel, silt, and/or clay (the alluvium). A floodplain is not altogether flat. It has a gentle slope downstream, from the side towards the center.
Send a note with the following information to log this earthcache as 'found':
1) name of this cache and number of people in your group
2) At this point, in which direction lies the river? (north, east, south, west)
3) Using your answer for question 2, which way does this floodplain slope downstream? (the slope may not even be too visible to the naked eye, it is so slight)
Sources:
-www.co.fresno.ca.us/ViewDocument.aspx?id=44005
-http://en.wikipedia.org/wiki/Floodplain
-Woodward Park Informational Signs