Waterlogging, Land Reclamation & Drainage Notes

Last reviewed 16 Sept 2026 · 7 min read

Waterlogging

Land is waterlogged when the water table rises so close to the surface that the root zone becomes saturated, air circulation in the soil is cut off and crop yields fall.

A commonly adopted Indian criterion classifies areas with a water table within about 2 m of the ground surface as waterlogged, and 2–3 m as potentially waterlogged (critical depth also depends on soil type, crop and groundwater salinity).

Causes

Seepage from unlined canals and distributaries — the main cause in canal commands.
Over-irrigation and intensive irrigation (excessive water application, no volumetric pricing).
Inadequate natural drainage — flat topography, obstructed natural drains.
Obstruction of drainage by roads, railway embankments, canal banks without adequate cross-drainage.
Impervious sub-soil (hard pan) close to the surface preventing percolation.
Heavy rainfall and flooding; submergence of low-lying land.
Seepage from reservoirs and irregular topography.

Harmful effects

Lack of aeration in the root zone — plants cannot respire; bacterial activity (nitrogen fixation) is reduced.
Soil remains cold — delayed germination; difficult tillage and delayed sowing.
Growth of weeds and aquatic plants.
Salinisation (efflorescence) — capillary rise of saline groundwater and evaporation leaves salts at the surface (white crust) → sterile land.
Restricted choice of crops; reduced yields.
Unhealthy climate — breeding of mosquitoes (malaria).
Weakening of foundations of buildings and roads.

Prevention and remedies

Lining of canals and watercourses to reduce seepage.
Intercepting (seepage) drains alongside canals.
Efficient water use — reducing irrigation intensity in affected areas, volumetric assessment, proper land levelling, improved methods (sprinkler, drip).
Optimum use of groundwater — tube well pumping (vertical drainage) and conjunctive use of surface and groundwater.
Improving natural drainage and providing adequate cross-drainage under embankments.
Surface and subsurface drainage systems.
Bio-drainage — plantations of high water-using trees (e.g. eucalyptus) along canals and in affected areas.
Changing cropping pattern (less water-intensive crops).

Soil salinity and alkalinity

Irrigation water always contains some salts; where drainage is poor, salts accumulate.

FormulaClassification of salt-affected soils (US Salinity Laboratory)

Soil	EC of saturation extract	ESP (exchangeable sodium %)	pH
Saline	> 4 dS/m	< 15	usually < 8.5
Sodic (alkali)	< 4 dS/m	> 15	usually > 8.5
Saline-sodic	> 4 dS/m	> 15	usually ≤ 8.5

Saline soils ("white alkali") — excess soluble salts (chlorides, sulphates of Na, Ca, Mg); white surface crust; soil structure is usually good. Plants suffer because high osmotic pressure reduces water uptake.
Sodic (alkali) soils ("black alkali") — high exchangeable sodium; clay disperses, soil becomes impermeable, hard when dry and sticky when wet; dark surface due to dispersed organic matter; high pH (often above 8.5).
Locally known in India as reh, kallar or usar lands.

Reclamation

FormulaLeaching requirement

L R = \frac{E C _{i w}}{E C _{d w}} = \frac{D _{d}}{D _{i}}

$E C_{i w}$ = EC of irrigation water; $E C_{d w}$ = permissible EC of drainage water (root zone); $D_{d}$ = depth of drainage water; $D_{i}$ = depth of irrigation water.

Depth of irrigation required: $D_{i} = \frac{D _{c}}{1 - L R}$ ( $D_{c}$ = consumptive use depth).

Saline soils — leaching with good-quality water (ponding or intermittent) combined with effective drainage to carry away the dissolved salts; scraping the surface crust; growing salt-tolerant crops during reclamation.
Sodic soils — sodium must first be replaced by calcium using chemical amendments: gypsum (calcium sulphate) — the most common; also pyrites, sulphur, press mud, calcium chloride, acids. Then leach the displaced sodium out with drainage. Green manuring (e.g. dhaincha), organic matter and salt-tolerant crops (e.g. rice, barley, berseem) help.
Saline-sodic soils — apply amendments before leaching; leaching alone would convert them into sodic soils.

Land drainage

Drainage removes excess surface water and lowers the water table to keep the root zone aerated and to leach salts.

Surface drainage

Open channels (field drains, collector drains, main drains) that remove excess rainfall runoff and irrigation tail water. Designed by Manning's formula for a design runoff (e.g. from a design storm of a few days' duration) with gentle slopes, stable side slopes and velocities that neither silt nor scour. Land shaping and grading support surface drainage.

Subsurface drainage

Type	Description
Tile drains / perforated pipe drains	Clay or concrete tiles with open joints, or corrugated perforated PVC pipes with envelopes (gravel or synthetic filters), laid below the root zone at a gentle slope; water enters through joints/perforations and flows to outlets
Mole drains	Unlined cylindrical channels formed in clayey subsoil by a mole plough; cheap but short-lived
Vertical drainage (tube wells)	Pumping groundwater to lower the water table; water reused for irrigation if quality permits
Open deep ditches	Where pipes are uneconomical; occupy land and need maintenance

Drainage coefficient — the depth of water (mm or cm) to be removed from the drained area in 24 hours; it fixes the capacity of drains.
Layouts: natural (following depressions), gridiron (parallel laterals on one side of a main), herringbone (laterals on both sides of a main at an angle), intercepting (drain across the path of seepage along the foot of a slope or along a canal).
Depth commonly around 1–2 m (below the root zone); minimum slopes and velocities chosen to avoid silting; envelopes prevent entry of soil.

Drain spacing

FormulaEllipse (Donnan) equation — steady state

S^{2} = \frac{4 K ( b ^{2} - a ^{2} )}{q}

$S$ = drain spacing; $K$ = hydraulic conductivity; $q$ = drainage coefficient (recharge rate, m/day); $b$ = height of the water table midway between drains above the impervious layer; $a$ = height of the water in the drains above the impervious layer.

Hooghoudt's equation (drains above the impervious layer, using equivalent depth $d_{e}$ ):

S^{2} = \frac{8 K _{2} d _{e} h + 4 K _{1} h ^{2}}{q}

$h$ = height of the water table midway above drain level; $K_{1}$ , $K_{2}$ = conductivities above and below the drain level.

Worked examples

Worked ExampleExample 1 — leaching requirement

Irrigation water has EC 1.2 dS/m and the crop tolerates root-zone drainage water of 6 dS/m. Consumptive use for the season is 80 cm. Find the leaching requirement and the depth of irrigation.

Solution. $L R = 1.2/6 = 0.20$ $D_{i} = \frac{80}{1 - 0.2} = 100 cm$ (20 cm goes to leaching)

Worked ExampleExample 2 — classification of soil

A soil has EC of saturation extract 6 dS/m, ESP 20 and pH 8.3. Classify it and suggest reclamation.

Solution. EC > 4, ESP > 15, pH ≤ 8.5 → saline-sodic. Apply gypsum first, then leach with good water and provide drainage.

Worked ExampleExample 3 — drain spacing (ellipse equation)

Drains rest on an impervious layer with water standing 1.0 m above it; the water table midway between drains is to be held at 2.0 m above the impervious layer. $K$ = 0.5 m/day and drainage coefficient 5 mm/day. Find the spacing.

Solution. $S^{2} = \frac{4 \times 0.5 \times ( 2. 0 ^{2} - 1. 0 ^{2} )}{0.005} = \frac{6}{0.005} = 1200$ → $S = 34.6 m$

Frequently tested points

Waterlogging: saturated root zone; commonly water table within about 2 m.
Main cause in canal commands: seepage from unlined canals; also over-irrigation, poor drainage.
Effects: poor aeration, salinisation (efflorescence), weeds, malaria.
Remedies: lining, intercepting drains, efficient irrigation, vertical drainage, bio-drainage, drainage systems.
Saline: EC > 4, ESP < 15; sodic: EC < 4, ESP > 15, pH > 8.5; saline-sodic: both high.
Saline → leaching + drainage; sodic → gypsum then leaching.
$L R = E C_{i w} / E C_{d w}$ ; $D_{i} = D_{c} / (1 - L R)$ .
Drainage coefficient = depth removed per 24 h; ellipse equation $S^{2} = 4 K (b^{2} - a^{2}) / q$ .
Layouts: natural, gridiron, herringbone, intercepting.

Common MistakeCommon mistakes

Leaching a saline-sodic soil before applying gypsum (it turns sodic).
Treating EC and ESP limits the other way round.
Using $b$ and $a$ measured from the ground surface instead of from the impervious layer.

Revision SummaryChapter summary

Waterlogging saturates the root zone, mainly due to canal seepage, over-irrigation and poor drainage.
It is prevented by lining, efficient irrigation, groundwater use, bio-drainage and drainage systems.
Salt-affected soils are saline, sodic or saline-sodic by EC, ESP and pH.
Saline soils are reclaimed by leaching with drainage; sodic soils need gypsum or other amendments first.
Surface and subsurface drains are sized by the drainage coefficient and spaced by the ellipse or Hooghoudt equations.

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Waterlogging, Land Reclamation & Drainage