Hydraulics & Water Management Flashcards

The 'precipitation rate' of an irrigation zone should ideally be matched to:

Answer: The soil's infiltration rate to prevent runoff and ensure efficient water absorption

The sprinkler precipitation rate (inches/hour of water applied) should not exceed the soil's infiltration rate (inches/hour the soil can absorb). When PR exceeds infiltration rate, water pools on the surface and runs off, wasting water and potentially causing erosion.

What is 'deep percolation' and why is it a concern in irrigation management?

Answer: Water moving below the plant root zone where it cannot be accessed by roots, representing wasted irrigation water

Deep percolation occurs when more water is applied than the soil's root zone can hold. The excess drains below the root zone, where it is unavailable to plants. This wastes water, energy, and fertilizer (which leaches with the water), and can contribute to groundwater pollution.

A hydraulic analysis of an irrigation system reveals that the system demands 25 GPM but the water supply can only deliver 18 GPM at adequate pressure. What is the best solution?

Answer: Split the system into additional zones so each zone's demand is within the available 18 GPM capacity

When system demand exceeds supply, the solution is to create more zones so each zone operates within the available flow capacity. This may require additional zone valves, wiring, and controller capacity, but ensures each zone receives adequate pressure and flow.

What is the relationship between water velocity, pipe diameter, and flow rate as described by the continuity equation?

Answer: Flow rate equals the cross-sectional area of the pipe multiplied by the water velocity — so for a given flow rate, smaller pipes have higher velocity

The continuity equation (Q = A x V) states that flow rate equals pipe area times velocity. For a constant flow rate, reducing pipe diameter increases velocity (and vice versa). This relationship governs pipe sizing — pipes must be large enough to keep velocity below 5 fps.

ET (evapotranspiration) for a specific plant in the landscape is calculated by multiplying the reference ET (ETo) by:

Answer: The crop coefficient (Kc) or landscape coefficient (KL) specific to that plant type

Reference ET represents the water loss of a reference grass surface. To determine actual water needs of a specific plant, the reference ET is multiplied by a crop or landscape coefficient. Turf grass might have Kc=0.8, while drought-tolerant shrubs might have Kc=0.3.

What is the purpose of an air/vacuum relief valve on an irrigation mainline?

Answer: To allow air to enter and exit the pipe during filling and draining, preventing vacuum conditions and air lock

Air/vacuum relief valves allow air to escape during pipe filling (preventing air locks that block flow) and allow air to enter during draining (preventing vacuum conditions that could collapse the pipe or cause backsiphonage). They are essential on large mainlines and pump systems.