Groundwater recharge using monsoon water redirection
I discovered “Innovations in Groundwater recharge” in a linked in thread “How to collect flood waters, to be used at a later date” . I found the approach compelling and wanted to share it here. During their tests it delivered substantial recharge of ground water levels that had been dropping during the prior decade. The locations where it can be applied are limited but with modification it’s use could be broadened. This system could be used in parts of China to increase food production with minimal investment especially the areas where excess water is available during the monsoon season.
Their approach has some similarity with grow dryland where both seek to use water from the rainy season. The Grow dryland seeks to capture and use water on the land where it falls to support trees that deliver edible fodder and nitrogen rich compost.
The Monsoon redirection approach captures water down stream and diverts it onto specially prepared fields where it can support flooded crops like rice. The flooded fields gives water time to soak into the ground and recharge the local water table rather than running to the ocean or creating downstream floods. Grow Dryland is most applicable for dry or rain fed farming areas especially those that are degraded or impacted by climate change. Grow dryland is best for areas where irrigation water is not available, erratic during dry years or where ground water is failing due to excess withdrawal. The Monsoon redirection approach is more applicable for irrigated fields where existing canals could deliver excess monsoon water.
One of the larger differences is Grow Dryland can be implemented by individual farmers to improve their income and stability during drought while the monsoon redirection requires modified regulations and government cooperation at the federal, state and local levels.
Use Monsoon waters to recharge water tables
- Deliver excess water during monsoons to farmers.
- Farmers modify their fields to hold the water on their fields to grow flooded crops like rice
- Flooded fields give the water time to soak in and recharge the water table.
- Reduces flood levels and silt downstream
- Reduces fresh water wasted when it drains to the ocean
- Can help avoid the need to build new disruptive reservoirs
- Can reduce water requirement during hot season due to greater retained water and ability to pump water from recharged water table.
- Requires active management to determine how much monsoon water can be diverted safely while retaining necessary stream flows.
- Negatively impacted when the monsoons do not arrive.
The main change is allowing irrigation companies to deliver water to farmers during the monsoon season while also training the farmers in how to modify their fields and retain the water on their fields. The Key limiting factor is that you need excess monsoon water that can be extracted without violating downstream water user rights.
Another innovation was building retention systems in flood canals to slow the water down and give it more time soak in. I suspect that on a dollar per dollar basis it will be cheaper to convert more fields unless extensive canals already exist and sit dry for parts of the year.
Grow dryland is still better for many locations
I still prefer the grow dryland system for many areas but they can be used in combination. Grow Dryland seeks to retain the first 4 inches of rain from any storm on the ground where it falls. It can work in dry areas where no irrigation canals exist. When implemented at sufficient scale grow dryland essentially recharges local water tables slowing the flow so downstream flows receive more consistent flow from seeps and springs. As such it avoids the need to build major water capture and redirection systems. On the other hand where those canals and diversion dams already exist the Monsoon redirection process could be implemented at lower initial cost.
The main limitation for grow dryland is that you need to be able to implement the micro capture system which works great on barren, degraded and unused land but is more difficult on land with established forests. The Monsoon recharge redirection is a great way to redirect runoff from these areas for beneficial use.
Thanks Joe Ellsworth
CTO of Air Solar Water