A moderate, widespread rainfall event occurred overnight April 15-16, concentrated in a ~3-hour window centered around 00:00-01:00 CST April 16 (05:00-06:00 UTC). This was the most spatially extensive rain since Event 4.
Spatial pattern — clear south/southeast concentration: - Richland zone (highest): 0.859" average — Headwaters Richland 0.877" (0.563"/hr peak), Falling Water Creek 0.841" (0.504"/hr peak) - Cave Creek: 0.689" (0.409"/hr peak) - Richland outlet: 0.679" (0.369"/hr peak) - Headwaters Big Creek: 0.615" (0.349"/hr peak) - Bear Creek zone: 0.528" average — Headwaters Bear Cr 0.580", Outlet Bear Cr 0.476" - Calf Creek: 0.527", Left Fork Big Creek: 0.511" - Boxley: 0.380" (0.177"/hr peak), Shop Creek: 0.450" - Ponca zone: 0.361" average - Pruitt zone: 0.304" average - Harriet zone: 0.432" average - St. Joe zone average: 0.451" (dragged up by high values in Richland-adjacent HUC12s)
Key characterization: This is a Richland/Cave Creek/Big Creek-centered event with moderate totals across the rest of the watershed. Peak 1-hr intensity of 0.563"/hr in Richland headwaters is moderate — well below flash-flood-producing intensities (>1"/hr sustained) but above typical detection thresholds.
Timing: QPE peak times cluster at 05:02-06:02 UTC (23:02 CST Apr 15 to 01:02 CST Apr 16), with nearly all rain falling in a 3-hour window. This is a compact burst event.
Boxley (07055646): Clear rise from 2.17 ft at 00:00 to peak 2.65 ft at ~13:00 CST (+0.48 ft). Currently receding at 2.55 ft. The rise was gradual — onset visible around 00:30 CST, steepest climb 08:00-10:00 CST (+0.13 ft/hr peak at 09:15). This is a confirmed Tier 1 (Detection) response at Boxley.
Ponca (07055660): Rose from 118 cfs at 00:00 to peak 167 cfs at ~17:00-17:30 CST (+49 cfs, +42%). Currently at 161 cfs and beginning to plateau/decline slowly. Ponca crossed above "Too Low" threshold (<150 cfs) around 14:00 CST and is now in "Low but Floatable" (150-200 cfs). This is propagation from the Boxley pulse with clear lag.
Pruitt (07055680): Essentially flat through EOD — oscillating 3.79-3.85 ft and 124-138 cfs. The noise amplitude (±0.03 ft) makes it hard to detect any signal. However, there are hints of a very slight rise in the final hours (3.83-3.85 ft from 20:30-23:30 CST vs ~3.80-3.82 earlier in the day). This may represent the leading edge of Boxley→Ponca propagation arriving at Pruitt, or it may be the start of local Cove Creek/Pruitt zone (0.30") response. Too early to confirm — watch Day 48.
St. Joe (07056000): Declined from ~308 cfs early to ~295 cfs late. The recession continued through the day without any clear interruption from the rainfall. However, the decline rate appears to have slowed: early morning readings averaged ~308-311, mid-afternoon ~298-304, evening ~295. This is consistent with continued recession rather than a response to today's rain. The Richland/Cave Creek/Big Creek rainfall (0.5-0.9") should produce a detectable signal at St. Joe within the next 12-24 hours based on Event 4 lag times.
Harriet (07056700): Small bump early in the day — rose from 3.99 ft / 396 cfs at EOD Apr 15 to 4.04-4.05 ft / 425-431 cfs around 01:15-05:00 CST, then declined back to 3.99 ft / 396 cfs by ~19:15 CST. The +0.05 ft / +29-35 cfs bump aligns with the timing of rain in Harriet direct sub-watersheds (0.41-0.48" in Water Creek, Tomahawk Creek, Dry Creek). Bear Creek gauge was flat (2.21 ft), confirming this was not from upstream propagation but from Harriet's local drainage. This is another example of Harriet's fast, brief local response pattern seen in Event 5.
Richland Creek (07055875): Major rise — from 1.25 ft at EOD Apr 15 to peak 1.81 ft at ~14:30 CST (+0.56 ft). This is the largest Richland response since Event 4 (which reached 3.58 ft). Currently receding slowly at 1.72 ft. The rise began around midnight, was steady through the morning, peaked mid-afternoon, and is now declining.
Bear Creek (07056515): Essentially flat at 2.21 ft / 19.8 cfs all day. Despite receiving 0.53" average rainfall, no detectable response. This is notable — 0.53" on moderately dry antecedent (only 0.03-0.06" 7-day prior) produced zero response at Bear Creek.
Boxley: 0.38" (Boxley HUC12) + 0.35-0.45" (Little Buffalo complex) → +0.48 ft - Rain timing: Peak at ~01:02 CST Apr 16 - Rise onset: ~00:30 CST (some rain started in late Apr 15 per prior day QPE of 0.47") - Peak: ~13:00 CST (+12 hr from rain peak) - Transfer ratio: 0.48 ft / ~0.82" total (combining Apr 15 + Apr 16 Boxley rain) = 0.59 ft/inch - Actually need to account for combined rain from Apr 15 (0.47") and Apr 16 (0.38") = 0.85" total - This gives ~0.56 ft/inch - Comparison to hypothesis: Previous observations: 1.038" → +0.87 ft (0.84 ft/inch, Event 1), 0.811" → +0.66 ft (0.81 ft/inch, Event 3, wet antecedent), 0.553" → +0.20 ft (0.36 ft/inch, Event 5). Today's ~0.85" → +0.48 ft (0.56 ft/inch) falls between Event 5 and Event 1. - Antecedent context: Boxley was at very low baseflow (2.15-2.17 ft) after 12 days of recession. 7-day antecedent was 0.67" (Boxley zone) but this included Event 5 remnants — the soil was probably moderately dry. The lower response ratio vs Events 1 and 3 (which had wetter antecedent) is consistent with the "filling the pools" effect from local knowledge. - Note on rain delivery: The rain fell in two pulses: a light precursor on Apr 15 evening (~0.10-0.29" per various Boxley/Little Buffalo HUC12s) and the main pulse overnight (~0.38" Boxley + 0.34-0.45" Little Buffalo). The spread delivery over ~6+ hours at low intensity likely reduced peak response compared to a concentrated burst.
Boxley → Ponca propagation: - Boxley rise onset ~00:30 CST → Ponca rise onset ~08:45-09:00 CST (going from 122 to 123 cfs): ~8-9 hr lag - Boxley peak ~13:00 CST → Ponca peak ~17:00-17:30 CST: ~4-4.5 hr peak-to-peak lag - This is slower onset lag but similar peak-to-peak lag vs previous events (4-5 hr Event 1, 1.75 hr Event 4). The slower onset is expected at these very low flow velocities.
Richland Creek: 0.86" (zone average) → +0.56 ft (from 1.25 to 1.81 ft) - Transfer ratio: 0.65 ft/inch - Comparison: Event 4 gave 1.65" → +2.63 ft (1.59 ft/inch) on moderate antecedent. The much lower ratio today (0.65 vs 1.59 ft/inch) despite similar antecedent wetness levels suggests strong non-linearity in Richland's response — consistent with karst character where lower rainfall amounts lose more to subsurface storage. - Comparison to local knowledge: Richland at 1.81 ft is well below the 3.2 ft "Low but Floatable" threshold. Not recreationally relevant.
Harriet local response: 0.43" (zone average) → +0.05 ft / +29 cfs - Response was fast: rain peaked ~00:00 CST, Harriet peaked ~01:15-05:00 CST (~1-5 hr lag) - Transfer ratio: ~0.12 ft/inch or ~67 cfs/inch - Comparison to Event 5: Event 5 gave 0.6-1.1" → +0.10 ft / +73 cfs. Today's ~0.43" → +0.05 ft / +29 cfs is roughly proportional. Confirms Harriet's local drainage produces fast, small, brief responses.
Bear Creek non-detection: 0.53" → no response - Antecedent was very dry (0.03-0.12" 7-day) - This confirms Bear Creek's high detection threshold. Even 0.53" with moderate intensity (0.27"/hr peak) on dry antecedent produces zero measurable response. Previous confirmed response required 0.63-0.71" as part of a multi-pulse event on pre-wetted soil (Event 4). Bear Creek detection threshold is likely 0.6-0.8" on dry antecedent, possibly lower on wet antecedent.
The Boxley→Ponca propagation is tracked above. The signal has not yet clearly arrived at Pruitt — the slight uptick in late-day Pruitt heights (3.83-3.85 ft from 20:30 onward) may be the leading edge. If so, Boxley→Pruitt lag would be ~20+ hours, consistent with Event 1 (20 hr) and Event 4 (21 hr from QPE). Monitor Pruitt on Day 48 for confirmation.
The Richland/Cave Creek/Big Creek rainfall should produce a signal at St. Joe. Based on Event 4, when similar HUC12s received 1.6-1.7" and the St. Joe response peaked ~33 hours later, today's ~0.5-0.9" in those areas should produce a smaller, later response. Expect a modest rise at St. Joe beginning late Day 48 or Day 49. The rise will be superimposed on the continuing Event 4 recession, potentially creating another recession analysis contamination issue similar to Event 5.
This event began with light precursor rain on Apr 15 evening (the "April 15 rain" noted as pending in the hypothesis). The main pulse arrived overnight Apr 15-16. The Boxley response integrates both pulses. Classify this as Event 6 with rainfall window Apr 15 evening through Apr 16 pre-dawn.
This event is interrupting the final phase of the Event 4 recession at all gauges. The recession analysis for Day 14+ will be contaminated. For St. Joe and Harriet, the Event 4 recession was still yielding 295-396 cfs at the time of interruption — both well above their 200 cfs Optimal threshold, so the practical effect is to extend their Optimal-range duration.
Bear Creek non-response despite 0.53" is informative but not surprising — it reinforces the high detection threshold for this watershed.
The recession halt/reversal at Harriet is noteworthy: Harriet was at 396 cfs and declining at EOD Apr 15, rose briefly to 425-431 cfs from local rain, then settled back to 396 cfs by late Apr 16. The arrival of the upstream propagation signal (from Richland/St. Joe zone rainfall) should bump Harriet again in 1-2 days. This event may effectively flatten Harriet's recession curve for 3-4 days, significantly extending its time above 200 cfs.
Ponca crossing into Low-but-Floatable is recreationally significant. The upstream pulse from ~0.85" in Boxley/Little Buffalo zone was enough to temporarily push Ponca from 117 cfs (below "Too Low") back to 167 cfs ("Low but Floatable"). Whether it sustains above 150 cfs depends on whether additional upstream propagation arrives. Given Pruitt zone also received 0.30" and Ponca zone 0.36", there should be some additional local contribution that helps sustain this level for 1-2 days.