Drainage ditches · peat · water table
The grid left by a peatland
On the plan, a ditch is a line. Water in peat is a surface. Close the sluices and watch what changes in the sections and what remains only a model assumption.
Sluices
Pressed button = sluice closed. You can also click the circle on the plan.
All segments passable
In the model, 6 of 6 segments are connected to the receiving channel. Close a sluice and see what changes in the sections and what does not.
Without JavaScript you see the initial state: all sluices open, both ditches passable. Switching sluices and comparing a reading need a script; the explanations and sources below work without it.
- solid white: ditch passable in the model
- dotted grey: ditch cut off
- black circle with a white bar along the ditch: sluice open
- white circle with a black bar across the ditch: sluice closed
- dashed orange: section line
- thick dashed light blue: water line in the peat according to the MODEL, the assumption selected for comparison (not a measurement)
- thin dotted: the other assumption about extent
- yellow diamond: a single number entered by the user, not Atlas data
Segments and sluices on the plan. S1: outlet to the receiving channel (dark strip on the right), sluice Z1. S2: eastern collector, crossed by line A–A′. S3: northern bypass ditch (the loop at the top of the plan), sluice Z4. S4: western collector, sluice Z2 just before the junction. S5: side ditch R3, crossed by line B–B′, sluice Z3. S6: southern ditch. The labels S1–S6 are not written into the drawing, to keep it uncluttered; this description stands in for them.
All the drawings are our own educational diagrams (not a map or a profile of Krowie Bagno). Sections: depth 0–2 m below ground, distance 0–25 m from the ditch edge, the same scale in both and in the close-up. The vertical scale is c. 3.6× larger than the horizontal (vertical exaggeration: 50 drawing units per metre vertically, 14 horizontally), so the ditch banks look steeper than the data imply; their shape is conventional. Horizontal lines every 0.5 m; heavier ones at 1 m and 2 m. The example water depths are model assumptions.
One piezometer reading: model or measurement?
Enter a water-depth reading at a single point. The page only calculates the difference between two numbers under two explicit assumptions about the extent of the drawdown. This is not a test of the model or an assessment of the peatland.
No reading
Enter both numbers and choose “Compare the two numbers”. Until you enter anything, there is no measurement point on the sections.
What the graph says and what it does not
Passability is not a water level
Close Z2 only: the western plots still drain through the northern ditch, and the sections do not change at all. Close Z2 and Z4: the connection of the western part disappears and R3 backs up. The graph settles whether a drainage route exists, not how much water flows along it or how deep the water stands in the peat.
A line is only a lead
A regular pattern of ditches visible on an orthophotomap points to ditches dug in the past, but it does not settle their present passability, direction of fall or degree of silting.
Water connects the fragments
Limiting outflow from ditches is one of the methods of rewetting peatlands. The effect requires understanding the whole hydrological system and monitoring; a single obstruction does not guarantee the same water level everywhere. [3]
First there was a lake
Krowie Bagno is a fen developed on lake sediments; according to PIG-PIB, lacustrine accumulation began at the end of the Vistula glaciation. [1] The Natura 2000 site covers the eastern part of a larger complex and is not the same as the whole peatland. [2]
Model assumptions used in the drawings
- Passable ditch: water in the ditch −1.25 m below ground; dammed ditch (sluice closed): −0.30 m below ground. Both values are assumptions of the diagram.
- The “background” level deep inside the plot: −0.50 m below ground, and −0.35 m when dammed. It is neither measured nor adjustable.
- Water line: h(d) = background − (background − water in ditch) · e−d/λ, where d is the distance from the ditch edge, λ = 14 m (wide) or 3.5 m (narrow). A conventional shape, not a solution of flow equations.
- Topology as in V2: S1 depends on Z1; S2 and S6 on S1; S3 on S2 and Z4; S4 on Z2 or S3; S5 on S4 and Z3. Segment S5 is a simplification of the diagram.
- No field data: directions of fall, ditch-bed elevations, peat parameters and observation dates are not known. They have not been entered as zeros.
What was removed from version V2
- The three-level “recharge” control: it hid the fact that the background is an assumption. Replaced by a fixed background and a comparison of two explicit assumptions about extent.
- Saving the reading in the browser (localStorage): unnecessary; the reading disappears on reload.
- A bar of five indicators and emoji icons: replaced by a single sentence of result.
- A photograph loaded from Wikimedia (it is not Krowie Bagno) and shared utility files: the page works offline; the link to the photograph remains in the sources.
From the grid to evidence
The article by Sikora and Cieśliński studies the Pobłockie peatland (Torfowisko Pobłockie) and Kurze Grzędy, not Krowie Bagno. It is a model of method: the authors compared historical maps with modern ones and then checked the network and installations in the field. It is not a ready-made layer of ditches for this case. [4]
- Documentation and maps: archival drainage documentation and topographic maps show the original design intent and the directions of fall of the ditch beds.
- Field verification and levelling: the elevations of the ditch beds must be measured, and the positions of sluices, vegetation blockages and the actual directions of flow established.
- Continuous piezometric monitoring: recording fluctuations of the water table in relation to rainfall and evaporation makes it possible to establish whether the network still drains the plot.