Levees constructed from soil are spaced at intervals of 0.10 to 0.25 feet elevation differences to maintain uniform water depths within each basin. Levee spacing may depend more on wind protection than on slope, since wave action in large expansive basins may cause seed burial by soil or seedling drift. Forming levees at 90-degree angles to the prevailing wind direction and restricting basin size to 20 acres or less helps control water depth and minimize wind damage. Field roads doubling as levees are often constructed around large fields to improve access and help contain water. Figure 18 .
Precision leveling with laser-guided equipment permits the formation of large rectangular basins.
Regulations to control pesticide movement into public waterways from rice fields mandate by law that the flow through outlet boxes be stopped for specific periods following the application of certain pesticides. Therefore, it is imperative to have an irrigation system that is easily controlled either within a field or within a recirculating water system. Figure 19 . A rice box or weir placed in a levee helps control water depth in a rice field. The goal of early season water management is to establish a vigorous, healthy, weed-free crop stand.