Hydrology: Analyzing River Flow Regimes and Hydrographs

River Flow Regime Analysis: Concepts and Classification

Fundamental Concepts of River Flow

• River Flow Basics: Refers to the seasonal variations in water discharge.
• Flow Module (Absolute Discharge): The absolute amount of water passing through a specific point in a river per second (measured in m³/s).
• Monthly Flow Coefficient (K): Calculated by dividing the average flow of a specific month by the annual average flow.
  • K = 1 indicates no change in flow rate (average flow).
  • K > 1 indicates higher than average throughput.
  • K < 1 indicates lower than average throughput.

Steps in River Regime Classification

1. Identify the Type of Regime

   Determine the primary source of water (snowmelt, rainfall, or mixed).

2. Identify the Geographic Area

   Determine the precise regions where the river may lie, based on the corresponding climate zone.

Understanding the Hydrograph

A hydrograph is a graph representing the change in stream flow (discharge) of a river at a particular point (gauging station) as a function of time. Flow is plotted on the vertical axis and the time scale on the horizontal axis. Its use is essential:

• To analyze the river regime (wide timescale).
• To analyze river flooding events (short timescale).

Classification of River Regimes

Nival and Mixed Regimes

These regimes are typically measured at elevated positions near the headwaters of rivers. They share the characteristic of having increased flow due to snowmelt during late spring and summer.

• Nival Regime (High Altitude)

  Occurs at points above 2500m. Highest discharge occurs in summer (K coefficient approximately +3) due to intense melting.

• Nivo-Pluvial Regime (Mid-High Altitude)

  Occurs at points between 2000m and 2500m. Highest discharge occurs in May (K coefficient approximately +2), followed by low water levels in summer (K coefficient approximately -1).

• Pluvio-Nival Regime (Mid Altitude)

  Occurs at points between 1600m and 1800m. Peak flow occurs in March–April. Experiences drought from summer to autumn.

Pluvial (Rainfall) Regimes

Flow rates correspond directly to the rainfall patterns associated with the specific climate zone.

• Oceanic Pluvial Regime

  Characterized by a high absolute flow module (e.g., +200 m³/s). Highest flow occurs in winter. Experiences mild drought.

• Continental Mediterranean Pluvial Regime

  Characterized by a low absolute flow module (e.g., -20 m³/s). Highest flow occurs in spring and autumn. Experiences significant drought.

• Eastern Mediterranean Pluvial Regime

  Low flow rate (e.g., -20 m³/s). Distinguished by three irregular peaks occurring in October, February, and May. Experiences mild drought.

• Subtropical Southern Mediterranean Pluvial Regime

  Very low absolute flow (e.g., -10 m³/s). Characterized by a long dry season (March to November). This regime is distinguished from nival regimes because its peak flow occurs in winter.