Elle Sagenev : Congratulations !!! I could not tell if you had seen the short video put out by Geoff Lawton on this subject, specific to your new issues !
Here is a link to that video :
http://www.geofflawton.com/fe/77036-flat-land-flash-floods
While you are at his site You might want to review one other of Geoff's videos, the - " A Tale of Two Neighbors " specifically dealing with using flooding
to gain Deposition of flood materials to stabilize your property and increase Humus and Fertility !
Good Luck, and keep us informed, merely exploring your 40 acres you will become part historian and part Sherlock Holmes ! For the Crafts ! Big AL