The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What factors determine whether a stream is permanent or ephemeral, gaining or losing? (A)

Permanent streams are watercourses that have a continuous flow of water throughout the year, while ephemeral streams only have water flowing during certain periods, usually after a rainfall event or during specific seasons.

A gaining stream is a stream that gains water as it flows downstream, typically due to the inflow of groundwater or other tributaries. A losing stream, on the other hand, loses water as it flows downstream, typically through infiltration into the ground, evaporation, or extraction for human use.

Several factors contribute to whether a stream is permanent, ephemeral, gaining, or losing, including: 1. Rainfall patterns: In areas with regular and sufficient rainfall, permanent streams are more likely to form, while in arid regions with sporadic rainfall, ephemeral streams are more common. 2. Groundwater levels: If a stream is recharged by a high groundwater table, it is more likely to be permanent and gaining, while streams with limited groundwater contribution may become ephemeral and losing. 3. Climate: In regions with high evaporation rates due to high temperatures and low humidity, streams are more likely to lose water and may become ephemeral. In cooler and wetter climates, streams may be better able to maintain their flow and remain permanent. 4. Geology and soil composition: Permeable rock formations and soil types can lead to losing streams, while impermeable layers can contribute to gaining streams as water is unable to infiltrate into the ground. 5. Human activities: Water extraction for agriculture, industry, or domestic use can reduce streamflow, turning a gaining stream into a losing one or making a perennial stream ephemeral.

By analyzing the factors mentioned in Step 3, such as rainfall patterns, groundwater levels, climate, geology, and human activities, one can determine whether a stream is likely to be permanent or ephemeral and whether it is gaining or losing water. It is the combination of these factors that ultimately determines the characteristics of a specific stream.