Q: What are some common devices used to measure flow?
A: Different methods to measure water flow for closed pipelines include propeller meters, orifice, venture, or differential pressure meters, and magnetic flux meters. Devices used to measure flow in open channels include weirs and flumes, stage discharge rating tables, and area/point velocity measurements. Ultrasonic devices, or travel time methods, may be used for both open and closed channels. Consideration in using open and closed meter as well as indirect methods requires attention to installation at each site. Improper installation can lead to inaccurate measurements. Important to note: volumetric measurements do not directly save water but they do provide information about costs associated with water use and efficiency of irrigation systems.

Q: What are the benefits of soil-moisture monitoring?
A: Soil moisture monitoring helps the producer from over-applying or under-applying irrigation water during application and throughout the growing season. In order to monitor soil moisture, it is important to know soil type and soil texture to better understand available water capacity for the plant or crop and field capacity, the balance between water moving downward through the soil profile and upward as in evaporation. Once information about field capacity is obtained then capillary force, the water stored in the root zone, can be determined. Some of this water is available to the crop while some of it is not. If the amount of water that a plant needs to sustain itself is not available, the plant will wilt, decreasing plant-water-soil optimization and eventually affecting maximum yield.

Q: What does the term evapotranspiration (ET) actually mean?
A: For most purposes, it is very difficult to separate the exact amount of evaporation and transpiration components of water within an actively growing plant community. Therefore, the term evapotranspiration, generally represented as ET, is usually employed for discussion purposes and for estimating the amount of water needed to meet water requirements of plants where some of the water will be going to evaporation and some to plant transpiration. The actual water used in metabolic processes is negligible. However, in order to meet plant needs, an additional amount of water must be applied to account for losses due to leaching in order to meet maximum ET demands and optimum plant growth rates. In agriculture, this is commonly referred to as irrigation efficiency and some irrigation systems are more effective in reducing water loss and improving efficiency.*

Q: What role does soil play in water movement?
A: When water reaches the land surface as precipitation, it can seep downward through pores between soil particles. Soil is made up of tightly packed particles of many shapes and sizes. A high porosity soil has the ability to hold large amounts of water due to the presence of many pore spaces. If the pores are well connected and allow water to flow easily, the soil is permeable. The size and shape of clay particles along with the arrangement of the pores between these particles result in clay soils being relatively impermeable and resistant to infiltration. Sands and gravels allow more rapid infiltration due to their high permeability. The initial water content of the soil is also important. In general, water infiltrates drier soils more quickly than wet soils. The intensity of a storm, or the length of time during which precipitation occurs, can also influence infiltration. If rain or snowmelt reaches the soil surface faster than it can seep through the pores, then the water pools at the surface, and may run downhill to the nearest stream channel. This limitation on the soil's capacity to allow infiltration is one of the reasons why short, high intensity storms produce more flooding than do lighter rains over a longer period of time.*

Q: How does capillarity affect soil water holding capacity?
A: One important characteristic of soil is its ability to hold water against the force of gravity and supply a portion of that water to plants. Much of this capacity is related to the number and size of pores and channels distributed throughout a soil. Some water can be held so tightly on polar surfaces in the soil that many atmospheres of pressure are required to force this water out. Plant roots must out-compete the forces that hold water in soil to survive, especially as more and more water is removed from the soil. However, much of this water would not even be in the soil in the first place without capillarity. All rainfall would drain rapidly from the soil and not be available for long-term use by many organisms nor would it be available for plant root uptake days or weeks after rainfall events. Most of the water available for plants in soil is that water categorized as capillary water.*