Today (March 1) saw the first meaningful rainfall of the study period, though amounts remained light. There is a clear west-to-east gradient with heavier totals in the eastern/downstream portions of the watershed:
Western watershed (headwaters, upper mainstem): - Boxley (HUC12 0201): 0.13" — highest in the upper watershed - Ponca zone: 0.18" average (Beech Creek 0.18", Smith Creek 0.14", Whiteley 0.21") - Pruitt zone: 0.25" average (Cove Creek 0.29", Hoskin Creek 0.20")
Central watershed (St. Joe tributaries): - St. Joe zone overall: 0.15" average, but highly variable by sub-group: - Little Buffalo complex: 0.11-0.17" (lower) - Big Creek complex: 0.09-0.18" (lower to moderate) - Cave Creek: 0.11" - Richland outlet: 0.10" - Mainstem misc: 0.04-0.22" (highly variable; Cane Branch 0.22", Calf Creek 0.12%, Rocky Hollow 0.22")
Eastern watershed (downstream): - Harriet zone: 0.26" average (Water Creek 0.32", Tomahawk 0.27%, Dry Creek 0.23%, Brush Creek 0.20%, Spring Creek 0.29") - Bear Creek zone: 0.14" average (Headwaters 0.11", Outlet 0.16") - Richland Creek zone: 0.10" average - Ungauged zone: 0.33" average — the heaviest totals in the watershed (Bratton Creek 0.37", Leatherwood 0.39", Hickory Creek 0.36", Long Creek 0.24%)
Peak intensities were low — max ~0.09"/hr (Tomahawk, Water Creek, Harriet zone). All rain appears to have fallen in a ~6-12 hour window in the evening/overnight period (peak 1hr times cluster around 00:06-03:06 UTC March 2, i.e., 6-9 PM CST March 1).
Gauge-measured precipitation: Pruitt 0.10", St. Joe 0.05", Harriet 0.19", Bear Creek 0.01". These are consistent with the west-to-east QPE gradient.
No significant rises detected at any gauge. All gauges continued their baseflow recession:
| Gauge | Start of Day | End of Day | Change | Notes |
|---|---|---|---|---|
| Boxley | 1.97 ft | 1.95 ft | -0.02 ft | Steady recession, now 1.94-1.95 range |
| Ponca | 89.2 cfs | 87.8 cfs | -1.4 cfs | Dropped one quantization step |
| Pruitt | 75.3 cfs | 72.3 cfs | -3.0 cfs | Continued decline; diurnal cycling confirmed (see below) |
| St. Joe | 183 cfs | 177 cfs | -6 cfs | Now firmly in "Low but Floatable" range |
| Harriet | 201 cfs | 201 cfs | ~0 cfs | Surprisingly stable; see discussion below |
| Richland | 0.96→0.98 ft (start) | 0.95 ft | -0.02 ft | Continued decline to new study-period low of 0.93 ft |
| Bear Creek | 8.2→7.7 cfs | 7.2 cfs | -0.8 cfs | Noticeable step down; now mostly at 7.67 quantization level |
Pruitt diurnal cycling — Day 3 confirmation: The pattern is now clearly established across three days. On 3/1: - Nighttime high: ~75-77 cfs (00:00-04:00) - Mid-morning decline to ~69-70 cfs (10:00-12:00) - Afternoon minimum: 67.9 cfs at 14:45 and 16:00 - Evening partial recovery: 70-74 cfs (18:00-23:00)
The amplitude today was 67.9-76.8 = ~9 cfs, slightly less than yesterday's ~13 cfs, consistent with the overall declining baseflow.
Ponca-Pruitt inversion update: Ponca ~87.8 cfs vs Pruitt ~72 cfs (mid-day). Deficit has widened to ~16 cfs. This is consistent with the hypothesis that relatively constant karst losses become a larger fraction of declining flow.
St. Joe notable feature: The height range today was 0.10 ft (3.43-3.53), wider than previous days (0.05-0.06 ft). The 3.43 ft reading at 13:00 and the 165 cfs discharge reading are unusually low, but the data bounces back immediately, suggesting this may be noise/sensor artifact rather than a real excursion. The discharge also shows a 165 cfs low at 13:00 — the lowest reading in the study period so far. The trend is clearly downward, with the afternoon readings settling around 174-177 cfs vs. morning 183-187 cfs.
Harriet appears to have stabilized: Despite continued recession at upstream gauges, Harriet's discharge has been remarkably stable at 197-201 cfs for the entire second half of the day. The morning readings were slightly higher (201-210 cfs range through ~10:00) then settled to a tighter 193-201 range by afternoon/evening, ending at 201 cfs. This is essentially flat relative to yesterday's close of 201 cfs. Possible explanations: (1) slow propagation of upstream baseflow is being offset by contributions from Harriet's own 430 km² local drainage plus Bear Creek's 239 km², (2) the light rain in the Harriet zone (0.26") may be providing just enough infiltration to slow recession, or (3) Harriet is approaching an asymptotic baseflow floor where karst springs dominate.
No detectable rainfall responses. With 0.10-0.33" of rain across the watershed (max 0.39" in ungauged Leatherwood Creek), zero gauges showed any rise attributable to precipitation.
Detection threshold update:
| Gauge | Rainfall (zone avg) | Max HUC12 in zone | Response | Antecedent 7-day | Conclusion |
|---|---|---|---|---|---|
| Boxley | 0.13" | 0.13" (single HUC12) | None | ~0.03" | 0.13" under very dry conditions: below detection |
| Ponca | 0.18" | 0.21" (Whiteley) | None | ~0.03" | 0.21" under very dry: below detection |
| Pruitt | 0.25" | 0.29" (Cove Cr) | None | ~0.01" | 0.29" under very dry: below detection |
| St. Joe | 0.15" avg | 0.22" (Cane Branch) | None | ~0.01" | 0.22" under very dry: below detection |
| Richland | 0.10" | 0.11" (Headwaters) | None | ~0.02" | 0.11" under very dry: below detection |
| Bear Creek | 0.14" | 0.16" (Outlet) | None | ~0.01" | 0.16" under very dry: below detection |
| Harriet | 0.26" | 0.32" (Water Cr) | None | ~0.01" | 0.32" under very dry: below detection |
Key finding: Under bone-dry antecedent conditions (essentially 0.0" 7-day prior to today's rain), up to 0.3" of widespread light rain over ~6 hours produces zero detectable gauge response. This is a significant result — it pushes the lower detection bound well above trace amounts. The soil moisture deficit must be fully satisfied before any runoff occurs.
Note: The rain fell primarily in the evening, so very late responses might not appear until tomorrow. Will check Day 2 data for any delayed response, though at these low totals it seems unlikely.
No propagation signal to analyze — all gauges in recession.
N/A — this is the first meaningful precipitation day.
Pruitt diurnal cycling confirmed (3 days). Confidence upgraded to Medium. The pattern is consistent: nighttime high, afternoon low, partial evening recovery. The amplitude appears proportional to baseflow level (~9 cfs today vs ~13 cfs on 2/28 when baseflow was higher).
Ponca-Pruitt deficit widening as predicted. Now ~16 cfs, up from ~12 cfs on 2/27 and ~14 cfs on 2/28. The karst loss appears to be a relatively constant ~12-18 cfs, becoming a larger fraction of declining flow.
Harriet stabilization is unexpected. All other gauges are declining 1.5-4%/day, but Harriet has been essentially flat (~201 cfs) for the past 24 hours after declining earlier. This could suggest a different baseflow regime at the lowest gauged point — possibly sustained by deeper karst springs that drain more slowly.
Richland Creek dropped to new low (0.93 ft). The afternoon readings (18:45-21:00) showed 0.93-0.95 ft, the lowest in the study. Richland is approaching what may be a near-zero flow condition.
The 0.3" detection threshold finding under dry conditions is important. It means the first rain event that actually produces a measurable gauge response will need to be at least 0.3-0.5" (rough estimate) to overcome the soil moisture deficit. After any significant wetting event, the detection threshold should drop substantially.