Vicampanavitz Conduction Line
New spring to new primary tank, Vicampanavitz, Nebaj, Quiché, Guatemala. Pipe sizing, head loss, pressure class, and valve layout on the total station survey, modeled in EPANET 2.2.
Pending · dry-season spring flow measurement…_SURVEY_capacity_check.inp
2-inch PVC, with 2½-inch for the last 841 m
The survey puts the spring only 13.1 m above the tank site, about 11 m less than the satellite estimate. With the inlet 2.5 m above the tank floor, 10.6 m of drop is available. An all-2-inch line would use 9.7 m of it at 0.8 L/s, leaving 0.9 m: under the 1 m minimum, and below zero once the pipe ages. Switching the last 841 m (station 70 to the tank) to 2½-inch cuts the loss to 8.3 m and leaves 2.3 m, or 1.1 m with aged pipe, for about 10% more PVC.
The model takes the spring box water level as the benchmark (station 1). If the water sits lower than the benchmark, subtract the difference from the 10.6 m. The dry-season spring flow is still unmeasured: if the spring gives 0.7 L/s or less, an all-2-inch line has enough margin (section 5).
What the total station changed
The survey has 96 points. Station 2 ("North") is the orientation shot beside the benchmark and is not on the pipe, which leaves 95 points from the spring to the tank site. Every point lies within 30 m of the GPS track (half within 9 m), so the survey follows the same alignment.
Stations 72 to 83 were recorded out of route order, which makes the sheet's running total jump back and forth. The sheet totals 4,071 m; in route order the line is 3,050 m measured flat, matching the GPS track's 3,048 m, and 3,143 m along the ground, including the 2.5 m riser up the tank wall. The model uses the route order shown in the appendix.
Elevations stay in the survey's own datum, with the benchmark at 1000.000 m. The sheet's "GPS Elevation" column adds 1,558.199 m, the handheld GPS reading at the benchmark; that reading was about 43 m low, so treat the column as relative heights, not true altitude.
| Point | Total station | Satellite (SRTM) | Handheld GPS |
|---|---|---|---|
| Valley bottom (lowest point each source found) | −172.0 m (st. 23) | −175 m | −153 m |
| Tank site | −13.1 m (st. 97) | −24 m | +23 m |
0.8 L/s on the busiest day of 2048
Unchanged from Rev A. The line is sized for the whole community's busiest-day demand at the end of a 20-year design period, following Guatemalan rural water criteria (INFOM). If the spring gives less in the dry season, the line carries whatever the spring gives.
| Step | Value | Basis |
|---|---|---|
| Households today × people each | 80 × 4.94 | Post-trip slides; Nebaj 2018 census (72,686 people, 14,708 households) |
| Population in 2048 | 615 | 2.03 %/yr growth (INE projection) for 22 years; covers the 20 planned homes |
| Water per person | 90 L/day | Top of INFOM's 60–90 L/day range for homes with a tap |
| Busiest-day flow | 0.77 → 0.8 L/s | Average 0.64 L/s × 1.2, rounded up |
How much drop each pipe size needs
Worked example: the recommended line at 0.8 L/s
- 2-inch section, 2,302 m. Water moves at 0.33–0.39 m/s. Hazen-Williams (C = 140) gives about 3.2 m of loss per km: 7.42 m including fittings.
- 2½-inch section, 841 m. The wider bore slows the water to 0.22 m/s, and the loss drops to about 1 m per km: 0.91 m including the exit into the tank.
- Total. 8.33 m used of 10.6 m available, so the inlet keeps 2.27 m of pressure. With aged pipe (C = 130) it keeps 1.07 m.
The available drop
| Spring box water level (benchmark) | 1000.000 m |
| Tank site (station 97) | 986.896 m |
| Tank inlet, 2.5 m above the floor | 989.396 m |
| Available | 10.604 m |
A layout works when its head loss plus 1 m of leftover pressure at the inlet fits inside this drop.
| Pipe | 0.5 L/s | 0.6 L/s | 0.7 L/s | 0.8 L/s | 1.0 L/s | Full-open flow |
|---|
Three ways to build it
| All 2-inch | Recommended mix | All 2½-inch |
|---|
When all-2-inch is enough
- Spring gives 0.7 L/s or less. At 0.7 L/s the inlet keeps 3.0 m (1.9 m with aged pipe).
- Tank inlet 1.0 m above the tank site instead of 2.5 m (a half-buried tank). The inlet keeps 2.4 m (1.0 m aged), but the tank's water sits 1.5 m lower, so every home downhill gets 1.5 m less pressure.
Why the 2½-inch pipe goes at the tank end
Upsizing saves the same head wherever it goes, so it belongs where the larger pipe is cheapest. From station 61 to the tank the no-flow pressure stays under 72 m, so the 2½-inch pipe can be the thin-walled 160 psi class. Upsizing in the valley would mean thick 250 or 315 psi pipe.
Pipe schedule and profile
| Stations | Size | Class | Length | No-flow pressure | Pipes |
|---|---|---|---|---|---|
| S1 → S12 | 2″ | 160 psi · SDR 26 | 376 m | 0–86 m | 137 |
| S61 → S70 | 2″ | 160 psi · SDR 26 | 401 m | 18–72 m | |
| S12 → S20 | 2″ | 250 psi · SDR 17 | 197 m | 86–143 m | 232 |
| S25 → S61 | 2″ | 250 psi · SDR 17 | 1,127 m | 64–141 m | |
| S20 → S25 (valley) | 2″ | 315 psi · SDR 13.5 | 200 m | 141–172 m | 36 |
| S70 → tank | 2½″ | 160 psi · SDR 26 | 841 m | 11–45 m | 148 |
| Total | 3,143 m | 553 |
| Result | New pipe (C = 140) | Aged pipe (C = 130) |
|---|---|---|
| Tank inlet pressure at 0.8 L/s | 2.27 m | 1.07 m |
| Lowest line pressure at 0.8 L/s | 3.4 m at station 85 | — |
| Highest line pressure at 0.8 L/s | 170.0 m (242 psi) at station 23 | — |
| Flow with the tank valve fully open | 0.91 L/s | 0.85 L/s |
| Flow at which the inlet drops to 0 m | 0.91 L/s. The line cannot carry 1.0 L/s; that would need all-2½-inch pipe. | |
Sensitivity, water hammer, and velocity
| Assumption | Head loss | Inlet pressure |
|---|---|---|
| Hazen-Williams, C = 140 (design); hand calculation of the delivered file agrees | 8.33 m | 2.27 m |
| Darcy-Weisbach, PVC roughness 0.0015 mm | 8.2 m | 2.4 m |
| C = 150, new PVC (manufacturer's figure) | 7.4 m | 3.25 m |
| C = 130, aged pipe with biofilm | 9.5 m | 1.07 m |
Water hammer
A pressure wave crosses the line and returns in about 15 seconds. Each class was chosen so no-flow pressure plus a sudden-closure spike at 0.7 m/s stays within the pipe's rating; the real full-open speed is only 0.44 m/s, which leaves extra margin.
| Class | Wave speed | Spike at full flow | Max no-flow allowed |
|---|
Use gate valves, not quarter-turn ball valves, and close each over a minute or more.
Low velocity
At 0.8 L/s the water moves at 0.33–0.39 m/s in the 2-inch pipe and 0.22 m/s in the 2½-inch section, below the 0.6 m/s guides ask for to keep sediment moving. No size reaches 0.6 m/s with a 10.6 m drop, so handle sediment with a sand trap at the spring box, washouts at the low points, and periodic flushing with the tank valve wide open.
Placed from the survey's high and low points
Main valves go at every high or low point that stands out by 5 m or more. The minor points stand out by 2.5–3.6 m; grade the trench to smooth them out, or add a valve if the ground won't allow it. Each valve must be rated for the no-flow pressure listed.
| Valve | Station | Distance | Elevation | Pressure, 0.8 L/s | No-flow |
|---|
| Crossing | Stations | No-flow pressure | Treatment |
|---|---|---|---|
| River, valley bottom | S22 → S23 | 171–172 m | Galvanized Schedule 40 steel where the pipe is exposed, anchored on both banks; washout at S23 |
| River | S31 → S32 | 137–138 m | Galvanized steel if exposed, or bury below scour depth with concrete cover |
| River and bridge | S56 → S57 | 101–103 m | Galvanized steel, strapped to the bridge or on its own supports; washout at S56 |
| Road | S25, S38 | 94–141 m | Bury deeper or run through a steel sleeve |
| Field road, trail, streets | S91 → S94 | 32–35 m | Bury deeper or run through a sleeve |
- Throttle valve at the tank inlet. Fully open, the line runs at 0.91 L/s. If the spring gives less, the spring box drains and air enters the line, so set this gate valve to match the spring.
- Overflow and sand trap at the spring box.
- Fittings in each zone at the same pressure class as the pipe.
Using the EPANET files
Vicampanavitz_conduction_SURVEY_design_0.8Ls.inp
Design run. SPRING is a reservoir at the benchmark (1000.000 m); TANK_IN draws 0.8 L/s at 989.396 m. Nodes are named by survey station (S3 to S96) and sit at their total station coordinates, so the EPANET map matches the survey.
Vicampanavitz_conduction_SURVEY_capacity_check.inp
Capacity run. TANK_IN becomes a free-discharge reservoir, and EPANET solves how much the line carries fully open. These two files replace the Rev A files built on satellite elevations.
- Open a file in EPANET 2.2 (free from the US EPA) and click Run.
- If the spring box water level differs from the benchmark, change the
SPRINGhead. - To test a different tank height, change the
TANK_INelevation; to test a flow, change its demand.
Method and station results
- Solver: EPANET 2.2 engine, steady state, SI units. A separate hand calculation of the delivered file gives the same 8.33 m and 0.91 L/s.
- Route order: each survey point placed by its position along the GPS track (the survey grid matches the GPS track to within 1.5° of rotation).
- Pipe lengths: 3D distance between consecutive stations, plus a 2.5 m riser at the tank.
- Friction: Hazen-Williams, C = 140; fittings K = 0.3 per pipe, plus entrance 0.5, two gate valves 0.2 each, exit 1.0.
- Pressure class: no-flow pressure plus a sudden-closure spike at 0.7 m/s within the ASTM D2241 rating. A 124 m stretch (S39–S46) that could take 160 psi is folded into the surrounding 250 psi run to keep the schedule simple.
- Inside diameters (Amanco Wavin): 2″ 55.70 / 53.21 / 51.38 mm and 2½″ 67.44 mm for 160 / 250 / 315 psi.
Station-by-station results, recommended design at 0.8 L/s (95 rows)
| Station | Distance (km) | Elevation (m) | Grade line (m) | Pressure (m) | psi | No-flow (m) | Pipe in | Field note |
|---|
References
- Total station survey of the conduction line route, EWB-USC, 2026
- Amanco Wavin, ASTM D2241 PVC pipe datasheet
- OPS/CEPIS (2004), design guide for rural gravity conduction lines
- Universidad del Valle de Guatemala thesis citing INFOM rural water criteria
- NIMD, Caracterización municipal de Nebaj
- EPANET 2.2 user manual