Day 18 (2026-03-18) — Extended Dry Recession, Day 7 post-Event 3 peak
Effectively zero precipitation across the entire watershed. The only non-zero QPE reading was a trace amount (0.003") in the ungauged Leatherwood Creek HUC12 (110100050508), which is hydrologically irrelevant. This is the third consecutive day of zero rainfall. The 7-day antecedent precip continues to decline slowly across all HUC12s, now ranging from 0.42" (Water Creek) to 1.28" (Beech Creek), with most sub-basins in the 0.5-1.0" range.
All gauges are in sustained recession with no rainfall-driven responses. End-of-day values and daily changes:
| Gauge | Start of Day | End of Day | Daily Change | Rate (%/hr) |
|---|---|---|---|---|
| Boxley | 2.33 ft | 2.27 ft | -0.06 ft | — |
| Ponca | 155 cfs | 145 cfs | -10 cfs (-6.5%) | ~0.27%/hr |
| Pruitt | 224 cfs / 4.22 ft | 206 cfs / 4.15 ft | -18 cfs (-8%) / -0.07 ft | ~0.33%/hr |
| St. Joe | 512 cfs / 4.45 ft | 429 cfs / 4.25 ft | -83 cfs (-16%) / -0.20 ft | ~0.70%/hr |
| Harriet | 642 cfs / 4.38 ft | 535 cfs / 4.22 ft | -107 cfs (-17%) / -0.16 ft | ~0.70%/hr |
| Richland | 1.28 ft | 1.24 ft | -0.04 ft | — |
| Bear Creek | 13.2 cfs / 2.44 ft | 12.4 cfs / 2.42 ft | -0.8 cfs (-6%) / -0.02 ft | — |
Key observations:
Ponca has dropped below the Too Low threshold (150 cfs). It ended the day at 145 cfs, crossing below 150 around 13:00 CST. This is the first time Ponca has been below the recreational threshold since the study began. It took 7 days post-Event 3 peak (547 cfs on 3/11) to reach Too Low on a drying trend.
Pruitt is approaching the Low-but-Floatable/Too Low boundary (200 cfs). It touched 197 cfs briefly at 18:15 CST before bouncing to 200-206 cfs by end of day. The height readings (4.12-4.15 ft range at end of day) show considerable noise (±0.02 ft), consistent with the local knowledge about river-right channel scouring at the Pruitt gauge affecting low-flow readings.
St. Joe continues accelerating recession. Dropped from 512→429 cfs (-16%) today, compared to 594→512 cfs (-14%) yesterday. The recession rate has increased from ~0.63%/hr on Day 17 to ~0.70%/hr on Day 18. The Day 16 "plateau" hypothesis is thoroughly refuted — St. Joe had a slow interflow drainage phase that masked the continued recession.
Harriet has finally broken its near-flat behavior. After holding remarkably steady at ~649 cfs through Day 17, Harriet dropped sharply today from 642→535 cfs (-17%). This is the steepest single-day decline at Harriet during the study. The Day 17 "near baseflow floor at ~630-650 cfs" hypothesis was incorrect — Harriet was receiving residual mainstem input from St. Joe that masked its own declining trajectory. Now that the St. Joe recession wave has propagated through, Harriet's decline has accelerated.
Harriet is now declining FASTER than St. Joe on a percentage basis, which is unexpected. At 535 cfs (Harriet) vs 429 cfs (St. Joe), Harriet is actually carrying more flow despite being downstream — but the gap has narrowed from ~140 cfs (Day 16) to ~106 cfs. This convergence suggests the Harriet zone's independent baseflow contribution is also draining out.
None — no rainfall to correlate.
No active wave to track. However, the recession timing reveals propagation of the recession wave: the decline that began at upper gauges (Ponca peaked Day 11, began declining immediately) is now reaching its most pronounced expression at Harriet (which held nearly flat through Day 17 but dropped sharply today). This ~7-day lag between Ponca beginning its post-Event 3 decline and Harriet's sharpest decline is consistent with the ~25-33 hour peak propagation lag observed in Events 2-3 — the baseflow recession is a much slower-moving phenomenon that integrates cumulative declining input over days rather than hours.
This is the continuation of the extended dry recession from Event 3 (peak 3/11-12). Now 7 days post-peak with only a trace of rain since the marginal 3/15 pulse. This is the longest uninterrupted recession period in the study to date.
Recreational status update: - Boxley: Too Low (2.27 ft, well below 3.2 ft for Boxley-Ponca section per local knowledge) - Ponca: Too Low (145 cfs, below 150 threshold) — crossed today - Pruitt: Low but Floatable (200-206 cfs at end of day, barely above 200 Optimal threshold) — will likely cross into Low-but-Floatable or Too Low tomorrow without rain - St. Joe: Optimal (429 cfs, above 200 threshold) — still comfortably above threshold - Harriet: Optimal (535 cfs, above 200 threshold)
Harriet's sudden acceleration is the most significant finding today. The hypothesis document estimated Harriet's baseflow floor at ~630-650 cfs based on its near-flat behavior through Day 17. Today's drop to 535 cfs (and still declining) invalidates that estimate by a wide margin.
Revised interpretation: Harriet's apparent "stability" through Day 17 was not baseflow — it was the balance between declining mainstem propagation input and Harriet's own interflow contributions. Once the mainstem input fell below a threshold, Harriet began draining its own stored water rapidly. This has implications for baseflow estimation: we should not interpret temporary plateaus as true baseflow floors without at least 3-5 days of near-constant values during zero-precipitation conditions.
The Ponca-Pruitt discharge discrepancy has evolved interestingly. At end of day, Ponca = 145 cfs and Pruitt = 206 cfs, a gain of ~61 cfs (42%) through the Pruitt zone (123 km²). This is a larger percentage gain than seen during higher flows, suggesting that local zone contributions (Cove Creek, Hoskin Creek) maintain relatively steady baseflow that represents a larger fraction of total flow as mainstem discharge declines. This is consistent with karst spring contributions in the Pruitt zone maintaining flow even as surface runoff diminishes.