The Floodplain Protocol: Bankroll Dam Height & Spillway Rules

You are a winning $1/$2 regular. Win rate tracks around 3 BB/100 after rake. Then you lose 14 buy-ins in six weeks—every line runs into sets, every float gets punished. Nothing in your strategy changed. The river system just flooded.

Most players respond by studying more ranges. The leak is usually upstream: the reservoir was never sized for the watershed you play in. "30 buy-ins for cash" is a bumper sticker, not engineering. GTO Wizard, Primedope, and BeatTheFish all converge on the same idea—required bankroll is an output of win rate, standard deviation, format, and how much ruin risk you accept—not a universal constant.

This piece is a Floodplain Protocol walkthrough: dedicated reservoir, watershed storm tables, the ruin math behind dam height, spillway triggers, intake gates, session flood warnings, one worked $1/$2 audit, three protocol violations. No FAQ block. No solver frequency cosplay.

Why Rule-of-Thumb Buy-Ins Fail

"Twenty buy-ins and you're fine" survives because it is easy to remember. It is not correct.

Two players both win at 2 BB/100. Player A's standard deviation is 75 BB/100 (tight full-ring). Player B's is 110 BB/100 (aggressive 6-max). Same edge, different storm intensity. Player B needs a taller dam—often 50–100% more buy-ins—to hold the same risk-of-ruin (RoR) target.

Tournament players face a separate watershed entirely. Top-heavy payouts mean one cold month can erase dozens of buy-ins even at 15–20% ROI. The classic 100-buy-in MTT rule (GTO Wizard cites 75–125; BeatTheFish uses 100 standard / 150 conservative) exists because field variance dwarfs cash-game swings—not because MTT skill matters less.

The shift: stop asking "how many buy-ins do pros use?" and start asking "how tall does my dam need to be for my inflow, my storm gauge, and my acceptable flood frequency?"

The Protocol — Five Components

Treat your poker money like a managed reservoir system:

Component	What it is	Your job
Reservoir	Dedicated poker-only bankroll, isolated from rent and groceries	Never mix life money into the pool
Watershed	Game format (NLHE cash, PLO, MTT, SNG, Spin)	Each format has different storm intensity
Inflow	Win rate (BB/100 cash; ROI% tournaments)	Track it honestly, after rake
Storm gauge	Standard deviation (BB/100 cash)	Higher SD = wilder floods
Dam height	Buy-in count × stack depth	Sized to target RoR, not vibes

Spillway = automatic move-down trigger when water drops below safe level.

Intake gate = controlled move-up or shot-taking when reservoir exceeds upper threshold.

Most bustouts are not strategy failures. They are hydraulic failures: dam too low, spillway rusted shut, or life-money diverted into the reservoir during a drought.

Dam Height by Watershed

Industry baselines assume roughly 1–5% RoR for "standard" play. Your exact number comes from plugging tracked stats into a variance calculator (Primedope for cash, GTO Wizard's BRM tools for MTT). Until you have data, use format-specific starting points:

Watershed	Conservative	Standard	Aggressive	Notes
NLHE cash (100bb)	50 BI	30 BI	20 BI	BeatTheFish / common live-room guidance
NLHE 6-max (reg)	65–75 BI	40–50 BI	25–30 BI	~2 BB/100 at 95 SD ≈ 68 BI (5% RoR); 3 BB/100 at 90 SD ≈ 40 BI
PLO cash	70 BI	50 BI	30 BI	SD often 100–160 BB/100—taller dam mandatory
MTT (large field)	150 BI	100 BI	60 BI	GTO Wizard warns 100 BI is aggressive for big fields
SNG / HU SnG	80 BI	50 BI	30 BI	Lower field variance than MTT
Spin & Go	200 BI	120 BI	75 BI	Extreme payout skew

Full buy-in means the standard max at your room—usually 100bb. A $50 short stack at $1/$2 is not a buy-in for dam-height math.

When stats exist: the ruin equation

Risk of ruin connects the four variables. For cash games, a common approximation (see PokerGods, Primedope) inverts to:

Required bankroll (BB) ≈ −ln(RoR) × SD² / (2 × win rate)

—where win rate and SD are both in BB/100, then convert to buy-ins by dividing by stack depth.

Example sketch: 3 BB/100 win rate, 90 BB/100 SD, 5% RoR target → ~40 buy-ins; at 1% RoR, same inputs need ~62 buy-ins (Primedope formula). The point is not memorizing the output—it is seeing why a 1.5 BB/100 winner at the same SD might need 100+ buy-ins, while a 5 BB/100 crusher tolerates fewer.

Never treat calculator output as gospel without 50k+ hands (cash) or 500+ tournaments (MTT). Early samples lie.

Spillways and Intake Gates

Static dam height is half the protocol. Dynamic rules handle droughts and surplus.

Spillway triggers (move down)

When reservoir drops to ~60% of standard dam height, open the spillway—move down immediately. No "one more session."

Standard dam	Spillway level (60%)
30 BI cash	18 BI → drop stakes
50 BI cash	30 BI
100 BI MTT	60 BI

BeatTheFish and most pros treat this as non-negotiable. The down-move is not failure; it is what keeps the climb-up possible after variance reverses.

Intake gates (move up / shots)

Two safe patterns:

Gradual climb: When bankroll hits ~150% of standard dam height for the next stake, take a defined shot—3 buy-ins (cash) or 5 buy-ins (MTT) at the higher level. Lose the shot bundle → return. Win → stay and re-evaluate at the next threshold.

Kelly ceiling (not Kelly target): Full Kelly says risk roughly your edge—a 5% ROI SnG player with $1,000 risks about $50 per game (GTO Wizard's HU SnG example). Full Kelly is a redline, not daily driving. Half-Kelly or quarter-Kelly captures most growth at a fraction of variance. If Kelly says $50 and you feel the $25 game, that is feature, not bug.

Never move up because you "played well this month." Move up when the reservoir, not your ego, clears the gate.

Session Flood Warnings

Dam height protects against weeks-long downswings. Session rules protect against today's tilt flood.

Rule	Setting	Why
Session stop-loss	3 buy-ins (cash)	Next hand after the third is statistically a tilt hand
Stop-win (optional)	2–3 BI	Locks profit before give-back
Time cap	4–6 hours live	Fatigue raises SD without raising win rate

Even solid winners expect 10–15 buy-in downswings at cash; aggressive 6-max regs see 20+. That is normal watershed behavior—not proof your strategy broke. The protocol fails when you raise the dam height in your head while the actual reservoir drains.

Worked Audit: $1/$2 NLHE, 100bb Stacks

Profile: Online 6-max, tracked 2.5 BB/100 over 80k hands, 95 BB/100 SD, standard 30 BI dam (conservative players use 50).

Item	Calculation	Result
Full buy-in	100bb × $2	$200
Standard reservoir	30 × $200	$6,000
Spillway (60%)	18 × $200	$3,600 → move to $0.50/$1
Intake gate (150%)	45 × $200	$9,000 → shot at $2/$5 with $600 (3 BI)
Session stop-loss	3 × $200	$600 — stand up

Current roll: $4,800 (24 BI). Above spillway. Stay at $1/$2. If roll hits $3,600, drop to $0.50/$1 today—even if last session was "bad luck."

If roll climbs to $9,000, fire one $2/$5 shot ($500–$600). Lose it → back to $1/$2 with $8,400 (still 42 BI at old stake—healthy). Win and stay → reassess after 10+ sessions at new level, not after one good night.

Three Protocol Violations

Violation	Symptom	Fix
Shared watershed	MTT roll sized for cash (30 BI)	Separate dam tables per format—never cross-contaminate
Rusty spillway	"I'll move down at 10 BI" but currently at 12 BI and reloading from checking	Trigger on roll, not feeling; life money is not a spillway
Intake without gate	Won 5 BI, jump two stakes, lose 15 BI, bust	Shots are bundled and capped—3 BI cash, 5 BI MTT

What to Track (Minimum Viable Gauge)

You cannot size a dam without inflow and storm data:

• Cash: hands, BB/100 win rate, BB/100 SD (from tracker or manual log)
• MTT: tournaments played, ROI%, average field size
• Both: stake, session length, notes on tilt events

Recompute dam height every quarter or after +30k hands / +200 MTTs. Win rate drifts; so should your gates.

---

The Floodplain Protocol is not pessimism. It is permission to play your A-game during the flood—because the reservoir was engineered for the storm your watershed actually produces. Size the dam. Set the spillway. Then worry about whether to call the river, not whether you can afford next week's rent.