← Atlas of Discoveries Version V2 Version V1 V3 · Sonnet
Cross-section of a ceramic segment with a view of a field in the bore Original drawing, not a photograph. The thick terracotta wall of the pipe surrounds a round bore. Inside the bore is a diagram of a field: the surface, the water table in the ground, a row of drain segments and a ditch in which the water stands above the outlet, yet the difference in levels keeps the discharge going.
Original drawing · not a photograph

Cross-section of a drain segment

Ceramic drains

Does a submerged outlet stop the discharge? Not submersion alone – what matters is the difference between two water levels.

A clay pipe under an arable field does not suck anything in. In this model water enters it through the joints between segments and flows to the ditch only when the water table in the ground lies higher than the level to which the discharge is meant to fall.

The picture in the bore is a diagram of a field in the default state of the cross-section below (W 0.4 m, R 0.8 m, outlet 1.0 m), not a measurement or a plan of any particular field.

See the two levels in the cross-section
Object
ceramic drain segment – schematic drawing
Photograph
none on this page; a link to someone else’s photo is in the sources
Dimensions
not given; the drawing has no scale
Content status
teaching model, to be reviewed by a hydrologist

From segment to field in three scales

The magnification changes, but the principle does not: water enters between the segments. These are three static drawings, with no controls.

  1. Scale 1 · segment

    Cross-section of a segment A terracotta ring of wall around a round bore. A blue band of water lies at the bottom of the bore. Schematic drawing, without dimensions.

    Wall and bore

    A cylinder of fired clay. The terracotta is the wall; the pale circle is the bore through which water flows. The model ignores seepage through the wall itself – a simplification for a hydrologist to check.

    Diameter and wall thickness: not given.

  2. Scale 2 · joint

    Joint between two segments in longitudinal view Two terracotta segments laid one after the other. Between them is a narrow gap filled with soil. Two blue arrows lead from the soil downward, through the gap, into the bore. Schematic drawing, without scale.

    The gap between segments

    The segments lie one after the other. In this model, water from the soil enters precisely through the joint. Joints that are too wide or damaged can also let in soil particles and lead to silting of the line.

    Width of the gap: not given.

  3. Scale 3 · field and ditch

    Field, row of segments and ditch – miniature A miniature of the main cross-section: on the left, soil with the groundwater level, with a horizontal row of segments below it; on the right, a ditch with water. Two dashed water levels show that the difference in their heights is what drives the discharge.

    Two levels, not just the pipe

    The drain lies at 1.0 m and ends in an outlet in the ditch. Whether water flows is decided by two levels: in the ground and in the ditch. The amber dimension line is their difference, ΔH.

    Go to the cross-section with adjustable levels

The main relationship · teaching diagram

Two water levels and one head difference

Levels are given as depth below the ground surface (m b.g.l.): a smaller number means a higher level. W – the water table in the ground, R – the water surface in the ditch; the drain outlet lies at a fixed depth of 1.0 m. Discharge values are in conventional model units, not litres.

The adjustment buttons need JavaScript. Without it you can see the initial state (W 0.4 m, R 0.8 m) and the full description of the rules below the drawing.

Outlet under water · flowing

Outlet submerged, yet discharge continues

Water in the ditch (R = 0.8 m) covers the drain outlet (1.0 m), but the water table in the ground (W = 0.4 m) is higher than the water in the ditch. Head difference: ΔH = 0.8 − 0.4 = 0.4 m. Submersion of the outlet alone does not stop the discharge – what matters is the difference in levels.

Head difference ΔH
0.4 m
Discharge Q (model)
6 units/h
Diagram of a field cross-section with a ceramic drain and a ditch Original teaching diagram, not a map and not a measurement. On the left is a field with the water table in the ground (W) marked, and below it a horizontal row of four segments with three joints. On the right is a ditch with water at level R. Blue arrows show the direction of flow; the amber vertical dimension line ΔH is the difference in levels. The current state is described by the text above the drawing. ΔH W R
Teaching diagram, without a survey scale; it is not a map, not a cross-section of any particular field and not an instruction. The vertical scale is fixed: 1 m of depth = 180 drawing units.
  • ceramic segment with three open joints
  • saturated zone below the water table W
  • amber: difference in levels ΔH
  • gate closed at the outlet

Hourly balance (conventional units, fixed scale)

  • Discharged to the ditch6 units
  • Stays in the profile as free water42 units
  • Bound, does not drain by gravity40 units

Free water: 48 = 6 + 42 units. The full width of the bar is 120 units.

Model rules (always visible)

Outlet under water, W higher than R
Flows below the surface of the ditch. ΔH = R − W, Q = 15 × (joint conductance) × ΔH.
Outlet above the water or level with it (R ≥ 1.0 m), W higher than the outlet
Free outlet (at R = 1.0 m the water reaches exactly the level of the outlet; at a larger R it stands lower). The head difference is measured to the level of the outlet: ΔH = 1.0 − W.
W and R at the same level
ΔH = 0, the discharge ceases even though the outlet is submerged.
R higher than W
The difference in levels acts towards the field; no discharge from the field takes place. Backflow is not calculated, so Q is ‘not calculated’, not zero.
W at the level of the outlet or deeper, free outlet
There is no free water above the drain; Q = 0.
Blockage or closed gate
Q = 0 despite the head difference. A gate is a retention decision; a blockage is a fault in the discharge path.

Free water drains away, while water bound by capillarity stays in the soil, so drainage does not dry the ground below field capacity.

Draining and retaining: two equal sides

Drainage

Pavilion 7 of the Museum in Szreniawa shows the history of land drainage on Polish lands. The official description of the exhibition lists tools and equipment for draining and irrigating land (according to the museum’s description; link in the sources).

Ceramic segments are one of the material traces of such work. This page gives no dates, places or numbers of former drainage networks, because no material on them was supplied.

Retention

According to Polish Waters (Wody Polskie), long-term drainage and the loss of wetlands contributed to water shortage. Modern water management also includes holding back and slowing down discharge, for example with gates, to store water before the summer drought.

In the cross-section, the gate stops the discharge even though a head difference exists. The model does not decide when retention is beneficial for a particular field.

Show the gate in the cross-section

Limits of the model and sources

Assumptions

  • Teaching, not design. The ΔH and Q calculations are a simplified gravity model in conventional units. It is not a drainage design, an instruction for rebuilding drainage, or proof that draining always improves the condition of the land.
  • Fixed parameters. Outlet at a depth of 1.0 m, a single conventional soil permeability, a steady state with no time or rainfall.
  • To be checked by a hydrologist: the rules on the difference in levels, the free-outlet condition, the omission of seepage through the segment wall, and the values 15 and 80 in the model.
  • No photographs. The drawings on the page are original diagrams. No photograph of a segment with a measuring scale, and no historical diagram of a network, was supplied.

What was removed compared with V2

  • Choice of soil profile and drain depth – fixed, because they did not change the main relationship between the two levels.
  • Comparison of field observations with the diagram – removed as an apparent diagnosis of an installation; replaced by a strip of results at each R and the rules above.
  • Sliders – replaced by large buttons in 0.2 m steps (touch and keyboard).
  • Photograph from Auckland Museum – not loaded from the web; only the link remains.

Sources

The links were carried over from V2; they were not opened again in V3. They need checking before publication.

  1. Muzeum Szreniawa: Wycieczka po muzeum [A tour of the museum] – scope of the exhibition in pavilion 7.
  2. University of Minnesota: How agricultural drainage works – ceramic segments and the soil water balance.
  3. University of Illinois: Subsurface Drainage – flow through joints and the causes of loss of passability.
  4. Wody Polskie: Susza? Retencja! [Drought? Retention!] – the effects of drainage and in-channel retention.
  5. Photograph (link only): Auckland Museum, two-channel drain segment no. 1998.81.40 – Wikimedia Commons, licence CC BY 4.0 according to the description in V2. It is not an exhibit from Szreniawa, nor the pipe from this model.