Downstream estimates add the Junction and Johnson Fork readings, each shifted by its travel time. Past the last reading, Junction follows the NWS forecast and Johnson Fork is assumed to recede by half every 6 hours. Creek inflow below Johnson Fork is not counted, so during local rain the real river will run higher than these numbers.
| Flow at Junction | to rm 7.3 | to Grobe | to Yates | to Mason |
|---|
Flood waves on the Llano move faster when the river is high. Matching 23 flood peaks between the Junction and Mason gauges (2002–2026, about 58 river miles) gives a travel time of 48.1 − 8.0 × log10(flow) hours, within about ±2.5 hours. Shorter reaches are scaled by river miles below the Junction gauge: Grobe ~11.5, Yates ~15.5. Field observations are used to tune these numbers.