State Water Resources Research Institute Program

Project ID: 2011CA275B
Title: Sustainable irrigation management of drainage impaired area with 'Natural Drainage'
Project Type: Research
Start Date: 3/01/2011
End Date: 2/29/2012
Congressional District: 44
Focus Categories: Irrigation
Keywords: Irrigation
Principal Investigator: Wallender, Wesley W
Federal Funds: $ 0
Non-Federal Matching Funds: $ 36,660
Abstract: Sustained irrigation practice is crucial to the San Joaquin Valley which contributes 50 percent of the state's agriculture revenue. The absence of adequate drainage due to topographic and environmental constraints has forced the western San Joaquin Valley to tackle problems of shallow water tables with high salinity in general and specific toxic trace elements in particular. The Bureau of Reclamation, under Court Order, is to provide drainage service to the area so as to maintain a long-term, sustainable salt and water balance in the root zone of irrigated lands, sufficient to ensure sustainable agriculture in the region. In March 2007, the Bureau of Reclamation decided to implement a combination of drainage reduction measures, drainage water reuse, evaporation ponds and land retirement in what it calls the In-Valley/Water Needs Land Retirement Alternative. The retirement of irrigated agriculture lands is one of the main component of the plan. The Bureau of Reclamation intends to retire up to a total of approximately 78,500 ha of land in the drainage area. Retired lands are assumed to be managed as dryland farming, grazing, or fallowing. However there are concerns about the lack of scientific data to identify potential benefits and impacts of retiring land from irrigated agriculture on a large scale. Some hydrologic and soil modeling studies have indicated that under some field conditions there is serious danger of retired lands becoming excessively salinized and seleniferous. In response to concerns about the lack of scientific data to identify potential benefits and impacts of retiring land from irrigated agriculture, a multi-agency team consisting of representatives from the Bureau of Reclamation (USBR), United States Fish and Wildlife Service (FWS), and the Bureau of Land Management (BLM) completed a five-year, large scale Land Retirement Demonstration Project (LRDP) at two drainage-impaired sites on the west-side of the San-Joaquin Valley (Erysian et al., 2005). Based on the five years of field data from the LRDP, Singh et al. (2009) developed a comprehensive theoretical and numerical modeling framework to evaluate the specific site conditions required for a sustainable land retirement outcomes based on natural drainage. The works of Singh et al. (2009) show the pathway to reducing the salinity levels without the encroachment of the shallow water table in the root zone. The results can be applied more broadly to the drainage management of drainage impaired lands. If the crop and irrigation is managed for salt balance such that leaching is constrained to match the natural drainage rate (defined as the downward flux from the shallow water table to the lower aquifer), the danger of rising water table is avoided. Singh et al. (2009) proposed a 'natural drainage approach' to sustainable land management for drainage impaired areas. With this approach it is feasible to design a sustainable land use regimen for drainage impaired lands in general and retired lands in particular. The key to the natural drainage approach is a priori knowledge of the relationship between the natural drainage rate and the depth to the water table from ground surface.

The proposed study aims to use the 'natural drainage approach' for sustainable irrigation management of drainage impacted areas. With an aim to achieve the goals, the objectives of this study are to:

  1. Collect field data on crop, irrigation, salinity, water table from the Land Retirement Demonstration Project and other drainage impacted sites in western San Joaquin Valley.
  2. Improve and update the numerical modeling framework of Singh et al. 2009 to simulate major processes occurring in the land phase of the hydrological cycle. The model simulates unsaturated-saturated water flow and solute transport, subject to root water uptake.
  3. Use parameter optimization (inverse modeling) technique to determine the natural drainage rate.
  4. Evaluate and recommend sustainable irrigation management strategies for the drainage impacted area with 'Natural Drainage" approach.
We propose to use HYDRUS 1-D and HYDRUS-2D software programs, which are finite element models for simulating movement of water, heat, and multiple solutes in variably saturated media. The control volume for the study will consist of the vadose zone including the root zone and the saturated zone. The drainage impaired sites are characterized by the presence of a barrier layer which divides the perched water layer from the unsaturated flow zone below the barrier layer. We are interested in representing five processes occurring in the land phase of hydrologic cycle. The processes that will be modeled include the evapotranspiration, unsaturated and saturated flow and the downward flux through the barrier layer. Solute transport in both the unsaturated and saturated zone is also required to quantify the changes in soil salinity in the vadose zone.

To calibrate the model, we will use PEST (Parameter Estimation) software. With the parameter optimization process, we will calculate natural drainage rate across the barrier layer as a function of hydrostatic head over the barrier layer. Based on the available data and the spatial extent of the perched water table condition, a series of site specific models will be derived to predict natural drainage rate as a function of hydrostatic head over the barrier layer.

The relation between the bottom flux and the groundwater head is the tool that allows one to estimate the natural drainage rate for the given site. The natural drainage rate is the main parameter that impacts the management option for the sustainable land use of the drainage impaired lands. The land use and water application practices are two of the main variables which can be changed to make sure that water table depth never rises above a predetermined level and the root zone salinity levels are maintained within a permissible level. To achieve these two objectives, the following options may be pursued during the simulation exercise, a) change in the land use, crop type, b) growing crops in only a part of the area each year, and c) intersperse dry land farming with other farming activities. We plan to coordinate and collaborate with interagency Land Retirement Demonstration Project and concerned water district to simulate and evaluate the consequence of a particular type of land use in the drainage impaired area of the western San Joaquin valley.

The research will result in the development of calibrated HYDRUS 1-D or HYDRUS 2-D models for a number of sites characterized by the perched water table and the natural drainage rate from the barrier layer. The calibration process using the PEST software will yield the natural drainage rate of the perched groundwater system as a function of hydrostatic head. We plan to prepare a contour map of the natural drainage rate covering the area characterized by the perched water table and downward flux through the barrier layer. The evaluated natural drainage rate can be used to develop a sustainable irrigation management of drainage impaired area. The developed model and its use will be shared with the concerned stakeholders such as Bureau of Reclamation (USBR), United States Fish and Wildlife Service (FWS), the Bureau of Land Management (BLM), Land Retirement Demonstration Project, and the concerned water districts.

Progress/Completion Report, 2011, PDF

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