1.2 Contact details of resource persons and institutions involved in the assessment and documentation of the Technology

{'additional_translations': {}, 'value': 1012, 'label': 'Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)', 'text': 'Land Use and Climate Change Interactions in Central Vietnam (LUCCi / GLUES)', 'template': 'raw'} {'additional_translations': {}, 'value': 1012, 'label': 'Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)', 'text': 'Land Use and Climate Change Interactions in Central Vietnam (LUCCi / GLUES)', 'template': 'raw'} {'additional_translations': {}, 'value': 1008, 'label': 'Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)', 'text': 'Technische Hochschule Köln (TH Köln) - Germany', 'template': 'raw'}

1.3 Conditions regarding the use of data documented through WOCAT

The compiler and key resource person(s) accept the conditions regarding the use of data documented through WOCAT:

Yes

1.4 Declaration on sustainability of the described Technology

Is the Technology described here problematic with regard to land degradation, so that it cannot be declared a sustainable land management technology?

No

1.5 Reference to Questionnaire(s) on SLM Approaches (documented using WOCAT)

2.1 Short description of the Technology

Definition of the Technology:

Return flow from paddy fields is strategically collected before being lost to rivers and is reused as an effective source of agricultural water.

2.2 Detailed description of the Technology

Description:

Return flow from paddy fields is defined as applied water that is not lost by evapotranspiration but returns to an aquifer or surface water body (Womach, 2005). The two types of return flow are surface and sub-surface. Surface return flow accounts for the major proportion. If surface return flow is strategically collected before entering rivers, it can be used as an ‘extra’ effective source of agricultural water supply (Phil King, 2008; Simons et al., 2015). Because paddies effectively purify water by absorbing nitrogen and phosphorus, this produces return flow of an acceptable quality for irrigation purposes. Return flow can be collected by drainage canals and stored in ponds and reservoirs, and then returned to pumps for reapplication. This technology offers one solution towards overcoming a deficit of irrigation water.

The goal of this technology is to store and reuse surface return flow from paddy farms to enhance irrigation efficiency. The purpose of constructing temporary barriers in drainage canals is to minimise water wastage and optimise the possibility of collecting and recycling surface return flow. Return flow from irrigation system is stored in surrounding ponds and reservoirs Return flow can only be used when it is captured in a storage structure or drain which has a hydraulic link to the irrigation source: thus an integrated framework for the reuse system consisting of both hydraulic, and management, links should be established. Within the scope of this study, the Water Management Unit (WMU) is understood as an integrated irrigation and drainage system consisting of four components: (i) the hydrological catchment which covers both non-irrigated and irrigated area; (ii) the source scheme generating return flow; (iii) the reuse scheme that is hydraulically connected with the source scheme; and (iv) a drainage system functioning as a harvesting as well as a supply structure.

Before implementing such a system it is recommended to analyse the correlation between irrigation efficiency and reuse of return flow, as well as developing a framework for managing and recycling return flow. Investigation aims at identifying the potential of return flow for irrigation; determining its quantity and quality; and developing an efficient and sustainable reuse framework. Water balance calculations, field measurements, water quality sampling and interviewing are all used for this purpose.

In the study area, long dry seasons cause severe water shortages and problems with saline intrusion. The study area is mainly covered by paddy, vegetables and other annual crops such as maize, sweet potatoes, peanuts and sugarcane. Paddy rice, which consumes a high proportion of the freshwater, is the dominant crop. Agricultural land in the downstream area is irrigated through gravity or pump irrigation systems. Here results indicate that the irrigation efficiency can be improved significantly: the irrigation efficiency of Tu Cau and Thanh Quyt irrigation schemes is projected to increase respectively by 1.8 and 1.4 times.

Reuse of return flow can be applied in all WMUs where the drainage canals are connected with storage tanks. Scientific and technical support tools are offered by the Vu Gia Thu Bon River Basin Information Centre. The centre was established in Danang providing a comprehensive information service to farmers and other water users – it includes capacity building and consulting services also.

2.3 Photos of the Technology

2.5 Country/ region/ locations where the Technology has been applied and which are covered by this assessment

2.6 Date of implementation

If precise year is not known, indicate approximate date:

• less than 10 years ago (recently)

2.7 Introduction of the Technology

Specify how the Technology was introduced:

• through land users' innovation
• during experiments/ research

3.1 Main purpose(s) of the Technology

• improve production
• conserve ecosystem

3.2 Current land use type(s) where the Technology is applied

Comments:

Major land use problems (compiler’s opinion): The lowland part of Vu Gia Thu Bon is an intensive agricultural area. Rice cultivation, which consumes a high proportion of fresh water, accounts for 70% of total agricultural land (Ribbe et al., 2011). Since 2005, due to the impacts of droughts and saltwater intrusion, water for irrigation during the dry seasons has become an increasing problem in the lowland area of this basin. Simultaneously, the irrigation efficiency of this region is relative low. Various measures are applied to address water scarcity for irrigation. Reusing return flow is regarded as a potentially new measure to reduce the severity of the irrigation deficit in dry periods.
Major land use problems (land users’ perception): Based on the information provided by the Department of Natural Resources and Environment (DONRE) for Quang Nam Province, this basin now faces the problem of temporarily insufficient irrigation water. This situation is caused by droughts, insufficient reservoir capacity, salinity intrusion and ineffective irrigation management.

3.4 Water supply

Water supply for the land on which the Technology is applied:

• full irrigation

3.5 SLM group to which the Technology belongs

• water harvesting
• surface water management (spring, river, lakes, sea)

3.6 SLM measures comprising the Technology

3.7 Main types of land degradation addressed by the Technology

Comments:

Main causes of degradation: crop management (annual, perennial, tree/shrub) (Paddy rice requires huge amounts of water. Meanwhile, the coefficient of irrigation return flow from paddy field is also quite high.), industrial activities and mining (Hydropower construction reduces water availability for irrigation), over abstraction / excessive withdrawal of water (for irrigation, industry, etc.) (It causes water waste and reduces irrigation efficiency.), change of seasonal rainfall (It affects the paddy water balance and actual irrigation need.), droughts (It causes saltwater intrusion.)
Secondary causes of degradation: change in temperature (It relates to evapotranspiration.), inputs and infrastructure: (roads, markets, distribution of water points, other, …), governance / institutional

3.8 Prevention, reduction, or restoration of land degradation

Specify the goal of the Technology with regard to land degradation:

• reduce land degradation

4.1 Technical drawing of the Technology

4.2 General information regarding the calculation of inputs and costs

other/ national currency (specify):

VND

If relevant, indicate exchange rate from USD to local currency (e.g. 1 USD = 79.9 Brazilian Real): 1 USD =:

20828.0

4.3 Establishment activities

	Activity	Timing (season)
1.	Building temporary barrier in drainage canal
2.	Dredging and expanding Sen Pond	12 months
3.	Installing and operating the temporary pump at Sen Pond, P is 15KW (Q=520-600m3/h)

4.4 Costs and inputs needed for establishment

	Specify input	Unit	Quantity	Costs per Unit	Total costs per input	% of costs borne by land users
Labour	labour		1.0	3046.52	3046.52
Equipment	machine use		1.0	5344.09	5344.09
Equipment	hammer, iron wire		1.0	2.4	2.4	100.0
Construction material	Stone,sandy bags,bamboo sticks		1.0	6.45	6.45	100.0
Construction material	Earth, concrete		1.0	1335.8	1335.8
Total costs for establishment of the Technology					9735.26
Total costs for establishment of the Technology in USD					0.47

Comments:

Duration of establishment phase: 12 month(s)

4.5 Maintenance/ recurrent activities

	Activity	Timing/ frequency
1.	Temporary barrier	each cropping season
2.	Temporary pump	annually

4.6 Costs and inputs needed for maintenance/ recurrent activities (per year)

	Specify input	Unit	Quantity	Costs per Unit	Total costs per input	% of costs borne by land users
Labour	labour		1.0	24.0	24.0	30.0
Equipment	machine use		1.0	38.41	38.41
Construction material	Stone,sandy bags,bamboo sticks		1.0	3.22	3.22	100.0
Total costs for maintenance of the Technology					65.63

4.7 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

Prices of the material and equipment; the approval procedure and disbursement process of the project of “Dredging and expanding Sen Pond”; the compensation cost for the farmers; the cost of operating and maintaining temporary pump; the cost of reinforcing the drainage canals.

5.1 Climate

5.2 Topography

5.3 Soils

5.4 Water availability and quality

5.5 Biodiversity

5.6 Characteristics of land users applying the Technology

Indicate other relevant characteristics of the land users:

Land users applying the Technology are mainly common / average land users
Population density: > 500 persons/km2
Annual population growth: 1% - 2%
1% of the land users are very rich and own 3% of the land.
2% of the land users are rich and own 7% of the land.
70% of the land users are average wealthy and own 60% of the land.
25% of the land users are poor and own 20% of the land.
2% of the land users are poor and own 10% of the land.
Off-farm income specification: There is a large industrial park located near the study site and a large part of the working population in the region is earning income by working in the factories.

5.7 Average area of land used by land users applying the Technology

5.8 Land ownership, land use rights, and water use rights

Land ownership:

• state

• farmer, individual

Water use rights:

• open access (unorganized)

• farmer, individual

5.9 Access to services and infrastructure

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

Water availability and quality

Other socio-economic impacts

Socio-cultural impacts

Ecological impacts

Water cycle/ runoff

Soil

Other ecological impacts

6.3 Exposure and sensitivity of the Technology to gradual climate change and climate-related extremes/ disasters (as perceived by land users)

Gradual climate change

Gradual climate change

	Season	increase or decrease	How does the Technology cope with it?
annual temperature		increase	not well

Climate-related extremes (disasters)

Meteorological disasters

	How does the Technology cope with it?
local rainstorm	well
local windstorm	not known

Climatological disasters

	How does the Technology cope with it?
drought	well

Hydrological disasters

	How does the Technology cope with it?
general (river) flood	not known

Other climate-related consequences

Other climate-related consequences

	How does the Technology cope with it?
reduced growing period	not well

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?

6.5 Adoption of the Technology

Of all those who have adopted the Technology, how many did so spontaneously, i.e. without receiving any material incentives/ payments?

• 51-90%

Comments:

By applying the technology, the potential reuse area of return flow is estimated about 33% of the study area (30.4ha of agricultural area is potentially irrigated by return flow). However, estimating the number of land user families that have implemented the technology is not the initial aim of the study. Therefore, it requires further detailed investigation and social survey as well.

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
Increases the water depth in paddy fields which helps to improve paddy productivity
Beneficial/ endangered species might obtain new habitats in the retention area

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
Using return flow is helpful to improve irrigation efficiency. The amount of extracting water for irrigation and the cost of operating an irrigation system can be reduced.
The measure contributes to mitigating negative impacts of drought and salt intrusion. During the dry season the river water becomes more and more saline due to salt water intrusion. Salinity also builds up from not leaching out salts in the subsoil
Take advantages of available drainage canals, ponds, reservoirs to reduce the investment costs
Acceptable water quality because of the purification function of paddies which removes nutrients from the water
Low costs of conveyance systems because of short distance. More flexibility of allocation because of stable return flow. Less conflict between sectors.

6.8 Weaknesses/ disadvantages/ risks of the Technology and ways of overcoming them

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be overcome?
Temporal and spatial variation causes difficulty in using return flow. The differences in soil type, terrain, storage capacity of the paddy fields and irrigation method (e.g. irrigation techniques, the amount of input water and pumping intervals) are major factors influencing the quantity of return flow	Constructing temporary barriers in the drainage canal helps to minimise the water wastage and optimise the possibility of collecting and recycling surface return flow.
Using return flow might spread diseases, and weed seeds from affected farms to safe farms	Encourage farmers to comply with the principles of prevention and control diseases in agricultural production. It is necessary to implement preliminary tests and analyses the quality of return water before recycling for irrigation purposes.

7.1 Methods/ sources of information

7.2 References to available publications

Title, author, year, ISBN:

Kim, H. K. et al. (2009) Estimation of irrigation return flow from paddy fields considering the soil moisture

Available from where? Costs?

Agricultural Water Management, 96(5), 875–882.

Title, author, year, ISBN:

Phil King (2008) Return Flow Efficiency

Available from where? Costs?

New Mexico Water Resources Research Institute

Title, author, year, ISBN:

Simons, G.W.H. et al. (2015) Water reuse in river basins with multiple users: A literature review

Available from where? Costs?

Journal of Hydrology. 558–571

Title, author, year, ISBN:

Ribbe et al. (2011) Annex 2 to Milestone Report 2011 - Description of the Study Region including an updated stakeholder analysis,

Available from where? Costs?

LUCCi project. ITT, Cologne University of Applied Sciences