Final answer:
Banks can use elevation data, like the ground being higher than the BFE, to determine flood insurance requirements. A LOMA from FEMA is necessary for official document verification. A flood event like the one in 2009 can potentially recur, which is analyzed through flood frequency graphs based on stream gauge data.
Step-by-step explanation:
If you find information showing the ground to be higher than the Base Flood Elevation (BFE), banks can indeed use that data when determining whether a flood insurance policy must be purchased. The elevation data might indicate that your property is outside the high-risk flood area. However, it is important to have this information verified and documented through proper channels, such as a Letter of Map Amendment (LOMA) from FEMA. If the accurate data is approved, banks can consider it when deciding on the necessity of flood insurance for a mortgage.
Regarding flood frequency, if a stream gauge recorded a discharge of 21,200 cubic feet per second (cfs) during the flood event of September 23, 2009, this data point would be plotted on a flood frequency graph. This graph can help to predict the likelihood of a similar event occurring, which relates to the question of whether a flood with a similar discharge could happen in the next 20 years. History and data suggest that such events can and do recur, although prediction always involves a level of uncertainty.