Stream restoration

Nahalal stream restoration project 

Background

The interface between streams and agricultural environments creates a shared space in which both systems influence eachother. In Israel, we have historically managed streams following a drainage engineering approach, which considered the stream as an obstacle to be “regulated” as much as possible, optimizing its function as a drainage channel, protecting farmlands from frequent flooding, and maximizing productive cultivated area. However, this approach degrades water quality and the stream’s ecological value, as well as its surroundings. Streambed incision, which disconnects the floodplain from the stream, combined with streambank erosion, are common problems requiring , repeated, expensive maintenance, questioning the economic feasibility and long term sustainability of this approach.

Recently, the Ministry of Agriculture and Rural Development has initiated efforts to implement a multidisciplinary approach aiming to create a more balanced and sustainable interface between stream channels and cultivated areas. Adoption of this approach is still limited, due to the scarcity of knowledge and lack of experience of both planners and drainage basin authorities. In addition, this approach will require both cooperation from the farmers and development of a compensation strategy, as there is an ongoing conflict between the owners of the agricultural land rights and the productive value of cultivation and the streams ecological needs

The Nahalal stream restoration project is a collaborative effort shared by four partners: i) the Soil Conservation and Drainage Department at the Ministry of Agriculture and Rural Development; ii) The Kishon River Drainage Basin Authority; iii) The Model Farm for Sustainable Agriculture at the Agricultural Research Center of Neve Ya’ar and iv) Israel Center for Streams and Watershed Management. This project aims to:

• maintain a long-term infrastructure for R&D, including monitoring activities of a stream in an agricultural watershed. The core research questions seek to examine and improve the interrelations and mechanisms in various situations where they currently are either deteriorated or restored and functioning.

• demonstrate ane ecohydrological restoration approach of Nahalal stream in a way that increases the ecosystem services provided to the surrounding environment, and to all users of the stream – farmers, visitors, and animals.

• transfer knowledge and information about costs and benefits of creating a restored, functioning stream system alongside a productive, food-producing agricultural system.

Project description

The Nahalal stream restoration project combines multiple intervention actions and in parallel vectors, all coordinated and synchronized towards realizing the above mentioned goals:
• Monitoring: Monitoring multiple metrics within the stream and at the stream/farmland interface, including water quality and vegetation dynamics.
• Planning and physical execution: The planning phase is scheduled to last six months, until June 2021, when Stage 1 of the commission (ecological rehabilitation) is set to launch. In the following year, landscape and access development actions are scheduled to be conducted. The project will include steps to restore both stream banks and the riparian corridor, with a program to restore a vegetation buffer strip along a 2.3 km section. Activities will include: removing dreged material consisting of soil mounds, eliminating invasive species; stabilizing gullies in the cultivated area; restoring channel and bank morphology; regulating runoff originating on farmlands; restoring a riparian buffer strip and planting native flora; rehabiliting ecological services in adjacent lands; monitoring pests/beneficial animals and weeds; and developing visitor infrastructure – with informative signs, protective fencing, a hiking path, and a river-course landscape t that includes shade and seating areas, providing visitors with a unique landscape/nature/educational experience of the valley’s rich agricultural heritage.
• R&D: Two directly-linked studies will occur simultaneously with the monitoring, planning, and execution activities: 1) a study on agricultural land restoration by returning dredged riverbed sediment to the field; and 2) a study on improving river/farm interface and empowering ecosystem services through restoring riverbank vegetation. Demonstration with Nahalal stream as a model will enable future adoption of this approach in other streams.
• Documenting, integrating, and disseminating knowledge through the Israel Streams and Watersheds Information Center and the Model Farm: Full documentation of the project will create a a database and project file defining specific practical tools and guidelines for professional practitioners involved in river restoration. This interdisciplinary effort will enable Implementing various tools to support improved stream management, primarily among a professional audience.

We identify numerous issues that face planning:
• The existing stream strip is narrow
• The flow regime is fragmented, due to reservoir operations. Floodwater and baseflow are harvested to a nearby reservoir for irrigation.
• Soil erosion processes deliver a considerable amount of sediment and sediment-bound agricultural chemicals, which are deposited in the stream channel.
• Water quality is degraded, both in the stream and in springs that feed the stream, with brackish water having high levels of nutrients (nitrogen)
• Hydraulic constraints exist that alter water flow, as seen in culverts and semi-Irish bridges that fix the longitudinal profile
• Establishing a clear connection between the monitoring results and planning & execution activities

Questions we ask ourselves:

• How to bridge the gap between the problems we identify in the stream and our wish to minimize anthropogenic intervention, i.e., utilizing low-tech process-based restoration? How deeply should we intervene?
• How to include uncertainty in stream planning and subsequent execution?
• To what extent should ecological goals dictate our objectives and benchmarks? How do we balance these with the agricultural goals
• What are suitable benchmarks for a project like this?
• Are there generic tools that can be adopted for planning stream restoration: calculating the river strip’s desired width? Longitudinal profile? Infrastructure? Flora composition? And so on