Indigenous knowledge of flood management and floodwater spreading in Qazvin traditional garden; deserves a new look at conservation and restoration

In arid and semi-arid regions of the world including Iran, floodwaters are the main resource to supply irrigation water. Floodwater spreading also plays an effective role in replenishing groundwater, stabilization of alluvial soil, and vegetation restoration. Qazvin traditional garden is an example of such floodwater spreading mechanism, dating back to over a thousand years ago, according to historical sources. The city of Qazvin is located at the foothills of the Aborz ranges and on the alluvial fan of the seasonal rivers. The traditional garden was built as a protective green belt around the city against floods. These unfenced gardens have been established as the largest aquifer in the region and an efficient flood spreading system to protect the city against floods. The gardens cover a vast area of around 2500 ha on three sides of the city. The unique practice of floodwater irrigation stabilizes the alluvial soil and recharges water in underground reservoirs. The gardens are placed next to each other in the form of ponds and are separated by borders with a height of about one meter. During the rainy season, the gardens are alternately filled with water up to the height of the ponds, which allow the water to infiltrate gradually into the soil. Almond, pistachio, and grape trees are irrigated once or maximum twice in months with very low evaporation. With such little irrigation, these trees survive and have economic efficiency. It is expected that the unique floodwaters irrigation of Qazvin traditional garden achieves its status in the strategic priorities of water management in the province.