Village Agriculture, Horticulture and Sericulture Assistant · Chapter 7

Watershed Management

What to remember

A watershed is the land area that drains rain water to one common outlet. Management means using land, water and vegetation of this area together, so that soil stays in place and water is stored.
"Ridge to valley" is the rule: treat the upper reaches first, then the middle, then the drainage lines and lower areas.
People's participation is the base: user groups, self-help groups and a watershed committee plan and maintain the work, and the community pays a share of the cost.

Meaning, size and terms

Watershed (catchment, drainage basin): a natural hydrological unit. All runoff from it leaves through one outlet (pour point).
Water divide (ridge line): the high line separating two watersheds.
Size classes (common usage): a micro-watershed is small (about 10 to 1,000 ha), a mini-watershed is about 1,000 to 10,000 ha, a sub-watershed is larger, and a macro-watershed or basin is the largest. Use a "check the guideline" approach for exact limits.
Runoff: the part of rainfall that flows over the land surface.
Infiltration: entry of water into soil. Percolation: downward movement through soil to the water table.
Recharge: addition of water to groundwater.
Water harvesting: collecting and storing rain water or runoff for later use.
Gully: a deep channel cut by flowing water. Rill: a small, shallow channel.
Water table: the upper surface of groundwater.

Why watershed management

Increase and stabilise crop production, especially in rainfed areas.
Conserve soil and reduce siltation of tanks and reservoirs.
Raise groundwater and improve drinking water.
Improve fodder, fuel and livelihood options.
Reduce flood peaks and increase base flow in streams.
Restore degraded land and increase green cover.

Characteristics that decide watershed behaviour

Factor	Effect
Size and shape	Long narrow shape has a lower peak flow than a round one
Slope	Steep slope gives fast runoff and more erosion
Soil type	Sandy soil takes in water fast; clay soil gives more runoff
Land use	Forest and grass reduce runoff; bare land increases it
Drainage density	High density means quick removal of water
Rainfall	Intensity matters more than total for erosion

Components of integrated watershed management

1. Land treatment (on the slopes).

Contour bunding, graded bunds, contour trenches, staggered trenches, field bunds.
Terracing on steeper slopes; bench terraces on high rainfall and steep land.
Land levelling and shaping, contour cultivation, strip cropping.
Mulching, conservation tillage and green manure to improve infiltration.

2. Drainage line treatment (in gullies and streams).

Loose boulder check dams, gabion check dams, brushwood dams, earthen dams.
Gully plugs and drop structures, grassed waterways, diversion drains.
These slow flow, trap silt and raise groundwater.

3. Water harvesting structures.

Farm ponds, percolation tanks, check dams and nala bunds, sunken ponds and village tanks.
Percolation tanks are designed to recharge groundwater, not to supply surface water.
Dug-out ponds and the "Neeru-Chettu" type of state programme supported tank and pond work in AP; check the latest official name.

4. Vegetative measures.

Afforestation and agro-forestry, horticulture and silvi-pasture.
Grass barriers such as vetiver or Cenchrus, live fences, shelterbelts and windbreaks.

5. Crop and farming system improvement.

Drought-tolerant and short-duration varieties, intercropping, crop contingency plans, in-situ moisture conservation.
Livestock, fodder and non-farm income activities.

6. Institutional measures.

Watershed committee, user groups, self-help groups and a watershed development team.
Training, capacity building and a watershed development fund to maintain assets.

Principles of watershed planning

Work from ridge to valley.
Treat the whole watershed as one unit, not field by field.
Plan according to land capability and soil depth.
Use simple, low-cost, local materials.
Keep rain water where it falls (in-situ), then the next level (nearby), then at the outlet.
Involve women, landless and small farmers, not only large landholders.

Programmes in India

Drought Prone Areas Programme (DPAP) and Desert Development Programme (DDP): area-based programmes from the 1970s.
Integrated Wastelands Development Programme (IWDP): treatment of degraded wastelands.
Watershed development guidelines (the 1990s onward) stressed participation and a common set of norms.
Integrated Watershed Management Programme (IWMP): combined DPAP, DDP and IWDP under the Department of Land Resources.
Pradhan Mantri Krishi Sinchayee Yojana (PMKSY, from 2015-16): its watershed development component continues the IWMP work. Its motto "Har Khet Ko Pani" means water to every field.
National Watershed Development Project for Rainfed Areas (NWDPRA) of the agriculture ministry.
MGNREGS funds many watershed works such as ponds, trenches and bunds in villages.
In AP, the government has used tank-restoration, farm pond and soil-moisture conservation programmes alongside central schemes.

Soil moisture and water balance in a watershed

Water balance: Rainfall = Runoff + Evapotranspiration + Infiltration (deep drainage) + Change in soil storage. Treatment aims to reduce the runoff part and raise the infiltration part.

Worked example 1: In a watershed of 100 ha, rainfall in a storm is 50 mm and runoff is 20 percent. Volume of rain = 0.05 m x 1,000,000 m2 = 50,000 m3. Runoff = 20 percent of 50,000 = 10,000 m3. (1 ha = 10,000 m2, so 100 ha = 1,000,000 m2.)

Worked example 2: A percolation tank has storage 6,000 m3 and 40 percent of stored water recharges the aquifer. Recharge = 0.4 x 6,000 = 2,400 m3.

Runoff coefficient C = runoff / rainfall. In the rational formula, peak runoff Q = C x i x A / 360 (Q in m3 per second, i in mm per hour, A in hectares). Example: C = 0.3, i = 60 mm per hour, A = 120 ha, so Q = 0.3 x 60 x 120 / 360 = 6 m3 per second.

Mulching, contour farming and bunds raise infiltration. 1 mm of rain on 1 ha equals 10 m3 (10,000 litres) of water.

Structures compared

Structure	Where built	Main purpose
Contour bund	On the slope, along the contour	Cut slope length, hold runoff in the field
Contour trench	On non-arable or hill land	Catch runoff and help tree planting
Bench terrace	Steep arable slopes	Convert the slope into level steps
Gully plug	In small gullies	Stop gully growth and trap silt
Check dam	Across a stream or nala	Slow flow, store water, recharge wells
Percolation tank	In permeable ground	Recharge groundwater
Farm pond	In the field or its corner	Store water for protective irrigation

Choosing treatment by slope

Land up to about 1 to 2 percent slope needs only field bunds and good drainage. Gentle slopes (about 2 to 6 percent) suit contour bunds and contour farming. Steeper arable slopes (about 6 to 15 percent) need graded bunds or terraces. Land steeper than this is best kept under trees, grass or horticulture with trenches. Shallow, stony soils are kept under grass or forest, while deep black soils on gentle slopes are managed with graded bunds and safe disposal of excess water. These slope bands are guideline values; follow the local technical guideline for design.

Excess water must leave the field safely. A grassed waterway is a broad, shallow, vegetated channel that carries the water without cutting a gully. Graded bunds guide water slowly to such a waterway, while level bunds keep water in the field.

Evaluating watershed work

Indicators used are: rise in water level in wells, increase in area irrigated, change in cropping intensity, reduction in soil loss, silt in tanks, green cover and farm income. Monitoring is by the committee and by the implementing agency.

Exam traps

Water divide separates watersheds; it is not the outlet.
Percolation tank recharges groundwater; farm pond stores water for direct use.
Treat from ridge to valley, not from valley to ridge.
Rill is small and shallow, gully is deep.
Check dams are built across drainage lines, not on slopes.
Infiltration is entry into the soil; percolation is deeper downward movement.
IWMP combined DPAP, DDP and IWDP.
Contour bund is on the slope; check dam is in the gully.

One-liners

Watershed is a natural hydrological unit with one outlet.
Work starts at the ridge and goes to the valley.
1 ha = 10,000 m2.
1 mm rain on 1 ha = 10 m3.
Check dams slow flow in gullies.
Percolation tanks recharge groundwater.
Vetiver grass is a popular vegetative barrier.
PMKSY motto is "Har Khet Ko Pani".
People's participation is the key to success.
Contour bunds follow the same level across the slope.
Runoff coefficient is runoff divided by rainfall.
Watershed treatment lowers peak flow and siltation.

Practice questions

A watershed is best defined as
1. an area with only one village
2. an area that drains runoff to one common outlet
3. a lake with a dam
4. a district boundary
Answer
B. an area that drains runoff to one common outlet
It is a natural hydrological unit.
The line that separates one watershed from another is the
1. water divide
2. pour point
3. water table
4. gully
Answer
A. water divide
The ridge line divides drainage.
Watershed treatment should proceed from
1. ridge to valley
2. valley to ridge
3. outlet to ridge only
4. the village to the market
Answer
A. ridge to valley
Upper reaches are treated first.
The point where all runoff leaves a watershed is the
1. summit
2. contour
3. divide
4. outlet or pour point
Answer
D. outlet or pour point
All drainage meets there.
Entry of water into the soil surface is called
1. runoff
2. transpiration
3. evaporation
4. infiltration
Answer
D. infiltration
Infiltration is entry; percolation is deeper movement.
A deep channel cut by flowing water is a
1. terrace
2. rill
3. gully
4. sheet
Answer
C. gully
Rills are small and shallow; gullies are deep.
Check dams are constructed
1. along field boundaries only
2. on hilltops only
3. across gullies and drainage lines
4. inside wells
Answer
C. across gullies and drainage lines
They slow flow and trap silt.
Percolation tanks are mainly built to
1. recharge groundwater
2. supply drinking water directly
3. breed fish
4. grow rice in the tank
Answer
A. recharge groundwater
Stored water seeps down to the aquifer.
A common vegetative barrier grass used in soil conservation is
1. lucerne
2. vetiver
3. paddy
4. maize
Answer
B. vetiver
Vetiver forms dense hedges that hold soil.
The motto 'Har Khet Ko Pani' belongs to
1. NWDPRA
2. PM-KISAN
3. DPAP
4. PMKSY
Answer
D. PMKSY
Pradhan Mantri Krishi Sinchayee Yojana.
IWMP was formed by combining
1. DPAP, DDP and IWDP
2. NHM, NFSM and RKVY
3. MGNREGS, PMGSY and ICDS
4. IADP, IAAP and HYVP
Answer
A. DPAP, DDP and IWDP
Three area-based programmes were merged.
Which is a land treatment measure on slopes?
1. Drop structure
2. Contour bunding
3. Gabion check dam
4. Gully plug
Answer
B. Contour bunding
The others are drainage line structures.
Which is a drainage line treatment?
1. Bench terrace
2. Strip cropping
3. Contour bund
4. Loose boulder check dam
Answer
D. Loose boulder check dam
Loose boulder structures go in gullies and streams.
Bench terracing is usually adopted on
1. flat lands
2. steep slopes in high rainfall areas
3. salt-affected lands
4. sandy deserts only
Answer
B. steep slopes in high rainfall areas
Terraces shorten slope length and hold water.
A farm pond is mainly used to
1. raise water table directly
2. produce hydro-power
3. store runoff for protective irrigation
4. grow only trees
Answer
C. store runoff for protective irrigation
Stored water supports crops in dry spells.
In a 1 ha field, 1 mm of rain equals
1. 10 cubic metres of water
2. 100 cubic metres
3. 1 cubic metre
4. 1,000 cubic metres
Answer
A. 10 cubic metres of water
1 mm x 10,000 m2 = 10 m3.
A 50 ha area receives 40 mm of rain. The volume of rainfall is
1. 2,000 m3
2. 200,000 m3
3. 40,000 m3
4. 20,000 m3
Answer
D. 20,000 m3
0.04 m x 500,000 m2 = 20,000 m3.
In a 100 ha watershed, 60 mm of rain falls and runoff is 25 percent. Runoff volume is
1. 25,000 m3
2. 60,000 m3
3. 15,000 m3
4. 6,000 m3
Answer
C. 15,000 m3
Rain = 0.06 x 1,000,000 = 60,000 m3; 25 percent = 15,000 m3.
A percolation tank stores 8,000 m3 and 30 percent recharges the aquifer. The recharge is
1. 5,600 m3
2. 3,000 m3
3. 2,400 m3
4. 240 m3
Answer
C. 2,400 m3
0.3 x 8,000 = 2,400 m3.
Runoff coefficient is defined as
1. runoff divided by rainfall
2. rainfall divided by runoff
3. runoff multiplied by area
4. infiltration divided by slope
Answer
A. runoff divided by rainfall
C = Q / P.
Using Q = C x i x A / 360 with C = 0.4, i = 90 mm per hour and A = 100 ha, peak flow is
1. 1 m3 per second
2. 10 m3 per second
3. 36 m3 per second
4. 3.6 m3 per second
Answer
B. 10 m3 per second
0.4 x 90 x 100 / 360 = 10.
If C = 0.25, i = 48 mm per hour and A = 150 ha, peak flow in m3 per second is
1. 12
2. 50
3. 0.5
4. 5
Answer
D. 5
0.25 x 48 x 150 / 360 = 1800 / 360 = 5.
The area of 250 ha in square metres is
1. 2,500,000
2. 25,000
3. 25,000,000
4. 250,000
Answer
A. 2,500,000
1 ha = 10,000 m2.
Which land use gives the least runoff?
1. Bare soil
2. Compacted road surface
3. Rock outcrop
4. Dense forest or grass cover
Answer
D. Dense forest or grass cover
Vegetation and litter raise infiltration.
Which soil gives more runoff for the same rainfall?
1. Sandy soil
2. Gravelly soil
3. Clay soil
4. Soil with high humus mulch
Answer
C. Clay soil
Clays take water slowly.
Which watershed shape gives a lower peak flow?
1. Square
2. Long and narrow
3. Circular
4. Fan shaped
Answer
B. Long and narrow
Runoff from different parts reaches the outlet at different times.
Consider the statements. 1. A water divide separates two watersheds. 2. A pour point is the high ridge line. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
The pour point is the outlet, not the ridge.
Consider the statements. 1. Percolation tanks recharge groundwater. 2. Check dams are built on the top of slopes. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
Check dams are built in drainage lines.
Consider the statements. 1. Watershed work involves people's participation. 2. Watershed work treats each field separately. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
The whole watershed is treated as one unit.
Consider the statements. 1. A rill is smaller than a gully. 2. Infiltration is movement of water to the water table. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
Downward movement to the water table is percolation or recharge.
Consider the statements. 1. IWMP was run by the Department of Land Resources. 2. PMKSY has a watershed development component. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
C. Both 1 and 2
Both are correct.
Consider the statements. 1. Contour bunds follow the same level across the slope. 2. Contour bunds run straight down the slope. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
Bunds on the contour hold water; straight bunds would speed the flow.
Consider the statements. 1. Mulching increases infiltration. 2. Mulching increases runoff. Which is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
Cover protects soil and slows water.
Match the pair: Gabion
1. a seed drill
2. a type of paddy
3. a rain gauge
4. stone-filled wire mesh box used in check dams
Answer
D. stone-filled wire mesh box used in check dams
Gabion structures are flexible and permeable.
Match the pair: Silvi-pasture
1. fish in rice fields
2. vegetables under net
3. trees combined with grass on the same land
4. only forest plantation
Answer
C. trees combined with grass on the same land
It gives fodder and fuel.
Match: Strip cropping is
1. growing one crop for years
2. growing different crops in alternate strips along contours
3. digging wells
4. burning crop residue
Answer
B. growing different crops in alternate strips along contours
It reduces erosion and runoff.
Which is an in-situ moisture conservation practice?
1. Cutting the forest
2. Digging a bore well
3. Building a large dam
4. Contour cultivation and mulching
Answer
D. Contour cultivation and mulching
In-situ means conserving water where it falls.
Which is a vegetative measure?
1. Farm pond lining
2. Live fences and shelterbelts
3. Gully plug
4. Gabion check dam
Answer
B. Live fences and shelterbelts
Plants are used to hold soil or reduce wind.
Raising the water level in wells is a sign of
1. successful watershed treatment
2. failed treatment
3. only high temperature
4. more erosion
Answer
A. successful watershed treatment
Recharge increases well water levels.
Watershed management is likely to make streams
1. flood faster
2. carry more silt
3. have lower flood peaks and more base flow
4. dry out completely
Answer
C. have lower flood peaks and more base flow
More infiltration feeds base flow.
Which scheme funds village works such as ponds, trenches and bunds through rural employment?
1. PM-KISAN
2. MGNREGS
3. NSAP
4. PMAY
Answer
B. MGNREGS
Natural resource management works are a core MGNREGS category.
The rational formula for peak runoff uses area in
1. square kilometres
2. acres
3. square metres
4. hectares
Answer
D. hectares
With Q = CiA/360, area is in hectares and Q in m3 per second.
Which is a measure of how fast a drainage network removes water?
1. Water table
2. Crop duration
3. Soil colour
4. Drainage density
Answer
D. Drainage density
High drainage density means quick removal.
Which of the following reduces siltation of tanks?
1. Burning grass
2. Soil conservation in the catchment
3. Cutting trees on slopes
4. Ploughing up and down the slope
Answer
B. Soil conservation in the catchment
Less erosion upstream means less silt downstream.
The upper surface of groundwater is the
1. runoff
2. water divide
3. water table
4. outlet
Answer
C. water table
Below it, soil pores are saturated.

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