u/SnooBunnies3511

If you collect daily puzzles, both of these might fit the rotation:

Drift is a daily word ladder. Start word, target word, change one letter at a time, every intermediate must be a real word. Has a theme reveal and shareable result line like Wordle's grid.

Wordform is a straightforward 5-letter / 6-guess Wordle clone with the standard color-coded feedback and a share button.

Both are free, no signup, no accounts. Just open the page and play.

- boardgaminghub.com/Drift.html

- boardgaminghub.com/Wordform.html

r/wordle has every Wordle clone under the sun, so I won't pretend mine is special - but I also built a daily word ladder (Drift) that I haven't seen many digital implementations of, and figured this is the right crowd for it.

Drift - daily start word → target word. Change one letter per step, every intermediate has to be a real word. Theme reveal at the bottom of the column. Numbered like Wordle so #1, #2, #3... and a shareable result string.

Wordform - my Wordle clone. 5 letters, 6 guesses, color-coded feedback, share button. Nothing reinvented.

Both are single HTML files, free, no signup, no accounts, no ads except AdSense pays the domain. Browser-only.

Drift: boardgaminghub.com/Drift.html

Wordform: boardgaminghub.com/Wordform.html

Bug reports welcome - just did a full audit pass across the hub last night.

I've been re-reading old E&S design references this week and ran into a claim I've heard repeated for years: "add a forebay to your sediment basin to improve trap efficiency." The figure I've seen quoted is something like +10 to +15 percentage points.

I tried to reproduce that with the actual arithmetic and I'm getting basically nothing. Want to sanity-check this with anyone who's worked the math themselves.

Setup. 5-acre residential subdivision, silt-loam soil, 22.2 cfs design peak inflow. Single basin sized to capture the 0.020 mm silt fraction per Camp's equation = 22,500 ft² surface area with the 1.2 short-circuit factor. Standard NRCS texture-triangle PSD for silt loam (8% sand / 12% VFS / 18% coarse silt / 22% medium silt / 15% fine silt / 12% very fine silt / 13% clay).

Single-basin trap efficiency (7-bin Stokes/Camp, η_i = min(1, v_s · A_s / Q)):

- Bins 1–4 all have η ≥ 1, so 100% capture → 60% of mass

- Bin 5 (0.010 mm): η = 0.30 → 4.5% of mass captured

- Bin 6 (0.005 mm): η = 0.075 → 0.9%

- Bin 7 (clay): η = 0.012 → 0.16%

Total: 65.5%. Below NCDEQ's 80% target.

Now add a forebay - say 10% of main basin (2,200 ft²). Series cells, both see the same Q. Forebay captures bins 1+2 fully, ~73% of bin 3, ~12% of bin 4, and basically nothing of bins 5–7. Mass captured by forebay: 36.3% of total. The 63.7% that overflows still has the entire bin 5/6/7 fines — they didn't settle in the forebay because v_s was too small for it.

Main basin sees the residual PSD and applies its same η table.

System total comes out at **66.0%**.

+0.5 percentage points for the forebay. Quadruple the forebay size to 8,000 ft² and you get to 67.0%. **+1.5 pp**.

The reason, I think, is the algebra of series capture: η_sys,i = η_fb,i + (1 − η_fb,i)·η_m,i. For bins where η_m already = 1, the forebay term collapses out. For bins where η_m < 1 (the only ones that matter), the forebay's η is *smaller* because A_s,fb < A_s,m. There's no configuration where the forebay does meaningful work that the main basin wasn't already doing.

What forebays are good for, as far as I can tell:

1. Concentrating coarse sediment in a small cell that's cheaper to clean

2. Dosing point for PAM (turbulent inflow gives the mixing PAM needs)

3. Resuspension defense — coarse sediment in the inflow zone is more vulnerable

4. Visible inspection (forebay full = needs cleanout, easier to gauge) All operational. None of them are "boost trap efficiency by 15pp."

My question for the sub: is there a configuration I'm missing where forebays meaningfully improve capture? Different influent PSD assumptions, non-plug-flow models, sequential decanting? I've seen the +15 pp claim in textbooks and I'd like to know if it's wrong, or if there's a regime where it holds.

Full worked example with all 7 bins, both single-basin and forebay configs side by side, sources, and the algebra:

hydrocomplete.com/examples/forebay-trap-efficiency-myth-worked-example.html

The two I've seen most often, in junior engineers and not-so-junior engineers alike:

1. Applying Kirpich to urban / mixed watersheds. Kirpich (1940) was calibrated on rural Tennessee farmland with 3-10% slopes and single flow paths. Plug it into a 200-acre suburban subdivision with mixed land cover and it'll under-predict Tc by 30-60%, which means over-predicting the rainfall intensity, which means over-sizing every pipe in the system.

2. Confusing NRCS lag T_L with Tc. T_L is 60% of Tc by NRCS's own documentation (NEH-630 Ch. 15), but a startling number of spreadsheets out there carry the lag value through as if it were Tc and end up sizing for the wrong storm duration on the IDF curve.

I put together a one-page comparison of every common method (Kirpich, NRCS Lag, TR-55 segmental, FAA, Kerby/Hathaway), with their validity ranges, side-by-side equations in US and SI units, and the common-mistakes list: https://pe-calc.com/cheat-sheets/time-of-concentration-methods.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=hydrology\_tc

And a worked end-to-end example showing TR-55 segmental on a 12-acre rural watershed (sheet flow + shallow concentrated + channel flow, then Rational Method, then HDS-5 culvert, then Manning's outlet velocity check): https://pe-calc.com/educational/culvert-sizing-worked-example.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=hydrology\_tc

Genuinely curious — what's the misapplication YOU see most? My default for anything urban or mixed is TR-55 segmental, Kirpich-only for true rural single-flow-path watersheds. Anyone using kinematic-wave methods on small watersheds in production work, or is it always TR-20 / HEC-HMS once you outgrow Tc-driven design?

Manning's n is a value civil engineers look up something like once a week, and it's almost always from a coffee-stained photocopy of table 5-6 in Chow's Open-Channel Hydraulics that's been Xeroxed through three generations and is now 60% gray. I made a clean single-page printable version for myself, then four more for the other values I keep looking up, then put them all online. Free, no login, sources cited at the bottom of each.

• Manning's roughness n (concrete to natural streams to floodplains): https://pe-calc.com/cheat-sheets/mannings-n.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=askengineers\_cheatsheets
• Hazen-Williams pipe coefficient C — separate columns for "new" and "design / aged" because manufacturer's "C=150" and AWWA M22's design value are not the same number: https://pe-calc.com/cheat-sheets/hazen-williams-c.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=askengineers\_cheatsheets
• Rational Method runoff C with the frequency adjustment Cf for higher-return-period storms (most undergrad refs skip Cf and just give you the 10-year values, which under-predict the 100-year peak by ~25%): https://pe-calc.com/cheat-sheets/runoff-coefficients.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=askengineers\_cheatsheets
• Weir discharge Cd — sharp/broad/V-notch/ogee/Cipolletti, with the Villemonte submergence correction: https://pe-calc.com/cheat-sheets/weir-coefficients.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=askengineers\_cheatsheets
• Tc methods compared (Kirpich vs. NRCS Lag vs. TR-55 segmental vs. FAA vs. Kerby) with validity ranges so you stop applying Kirpich to urban watersheds: https://pe-calc.com/cheat-sheets/time-of-concentration-methods.html?utm\_source=reddit&utm\_medium=social&utm\_campaign=askengineers\_cheatsheets

Sources cited on each: Chow, AWWA M11/M22/M23/M55, ASCE/WEF MOP-37, USBR Water Measurement Manual, McCuen, NRCS TR-55, FHWA HEC-22.

What's the reference card the rest of you wish existed but doesn't? I'm in a building mood.