P1A 03 Flood Hydrograph Interpretation: Study Guide

How does geology/soil type influence hydrographs?

• Permeable surfaces increase surface runoff and shorten lag time.

• Impermeable surfaces allow more infiltration, reducing surface runoff.

• Permeable surfaces allow more infiltration, reducing surface runoff and increasing lag time.

• Impermeable surfaces decrease peak flow and increase lag time.

How does seasonality (climate/weather) affect hydrographs?

• Intense summer thunderstorms cause rapid surface runoff and short lag times.

• Gentle winter drizzle allows more infiltration and less rapid response.

• Snowmelt in spring can cause significant flooding.

• Heavy autumn rains lead to prolonged drought conditions.

What is lag time in a hydrograph?

• The time difference between the peak rainfall event and the peak discharge of the river.

• The duration it takes for water to travel from the source to the river mouth.

• The time taken for a river to return to its normal flow after a flood.

• The interval between two consecutive rainfall events.

What does a 'gentle' hydrograph indicate?

• A 'gentle' hydrograph has a shorter lag time and higher peak discharge, typically associated with intense rainfall.

• A 'gentle' hydrograph has a longer lag time and lower peak discharge, typically associated with less intense rainfall, permeable surfaces, gentle slopes, and large drainage basins.

• A 'gentle' hydrograph indicates rapid runoff and high flood risk due to steep slopes.

• A 'gentle' hydrograph is characterized by frequent and heavy rainfall events leading to quick water accumulation.

What is baseflow?

• The portion of river discharge derived from groundwater flow, which sustains river levels during periods without rainfall.

• The total volume of water flowing in a river at any given time.

• The amount of water that evaporates from a river's surface.

• The flow of water that occurs during heavy rainfall events.

What does a 'flashy' hydrograph indicate?

• A 'flashy' hydrograph has a long lag time and low peak discharge, often associated with light rainfall and large drainage basins.

• A 'flashy' hydrograph has a short lag time and high peak discharge, often associated with intense rainfall, impermeable surfaces, steep slopes, and small drainage basins.

• A 'flashy' hydrograph indicates a stable flow with minimal changes in discharge over time.

• A 'flashy' hydrograph is characterized by gradual increases in discharge and is typically seen in areas with dense vegetation.

How does human activity influence hydrographs?

• Urbanization leads to increased infiltration rates.

• Agriculture reduces surface runoff significantly.

• Deforestation can increase surface runoff and alter hydrograph characteristics.

• Urbanization has no effect on hydrographs.

What is peak flow/discharge?

• The average rate of water flow in a river over a year.

• The highest rate of water discharge reached by the river during or after a storm event.

• The minimum flow rate of a river during dry seasons.

• The total volume of water that a river can hold at any time.

How does the size of the drainage basin affect hydrographs?

• Larger basins have a faster response and shorter lag times.

• Smaller basins receive more total precipitation and have a longer lag time.

• Larger basins receive more total precipitation and have a longer lag time.

• Smaller basins have a slower response and longer lag times.

What is the rising limb of a hydrograph?

• The part of a hydrograph where river discharge is decreasing.

• The initial part of a hydrograph where river discharge is increasing. Its slope indicates the speed of the discharge increase.

• The section of a hydrograph that represents the peak discharge.

• The final part of a hydrograph where river discharge stabilizes.