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FIS Flow Transfer

published points in, your site out — all eight flows.

Paste the FEMA Summary of Discharges rows for a stream, type the drainage area at your site, and get the 2-, 5-, 10-, 25-, 50-, 100-, 200- and 500-year flows. Every number the tool made is colour-coded, and every printed value that doesn’t sit on its own stream’s line gets flagged.

1 · Paste the table

Copy the rows straight out of the FIS PDF — one stream or the whole page, header included or not. Location text with numbers in it (“4,730 feet”, “river mile 125.2”) is fine: each row is read from its last number backward. An asterisk or dash counts as an empty column, not a skipped one.

2 · Check the rows

This is what the tool read. Fix any number here — you’re editing the input, so everything below updates. Untick a row to leave it out. If the paste held more than one stream, pick the one you want.

3 · Your site

The fallback exponent is only used when the published points can’t give a believable one (one point, two nearly equal areas, or a fit outside 0.3–1.0). 0.70 is a placeholder, not a published Tennessee value — put in a better one if you have it.
printed in the FIS interpolated extrapolated (range below) fallback exponent or far out — read the note don’t use without checking printed value off its stream’s line

4 · The published rows, filled

Each published row with its missing return periods filled in, and the exponent each column of the stream follows.
Show the math





How it works



  
Step one runs across return periods. Within each published row, flow is plotted as log Q against the standard normal value of the exceedance probability — the axis of flood-frequency paper. With three or more printed values the tool fits a gentle curve (a quadratic on that paper, kept only if it rises the whole way); with two it uses a straight line. The curve is pinned to the printed values, so it never moves a number the FIS gave you. A return period between two printed ones is interpolated; one beyond them, like a 2-year from a table that starts at the 10, is extrapolated and carries a range: the spread between the curve, a straight line through all points, and a straight line through the two printed values nearest that end.

  
Step two runs along the stream. For each return period, flow is carried by drainage area as Q = Q₁ × (A / A₁)b. A site between two published points takes the straight log-log line between that pair. A site beyond them is carried from the nearest point using the exponent b fitted through every point on the stream, and its range spans the believable exponents.

  
The guards. With four or more points in a column, each printed value is checked against a line fitted through the other points; one that misses by more than 1.5% (and well beyond the stream’s usual scatter) is struck through and left out of the math, with the line’s value shown beside it. A pair of points whose flow rises far faster than area, or falls as area grows, is the signature of a tributary, a dam, or two studies stitched together — anything the tool computes across it turns red. Two points within 10% of each other can’t give a usable exponent for extrapolation, so the fallback is used and said so. A site more than half again beyond the nearest point is marked; more than twice is red. Those thresholds are this tool’s own rules of thumb.

  
What it can’t know. It doesn’t know where tributaries come in, where dams sit, or whether a published drainage area is right. It only reads what you paste. Check every number you use.