gen-define-the-hydrograph-and-give-one-short-worked-example-85e2

Define the hydrograph and give one short worked example.

# Hydrograph Definition A **hydrograph** is a graph that shows the variation of discharge (flow rate) of a river or stream over time at a specific point. It typically plots: - **X-axis**: Time (hours, days, or months) - **Y-axis**: Discharge (m³/s or cumulative feet per second - cusecs) Hydrographs are used to analyze streamflow response to precipitation events, snowmelt, or other water inputs. --- ## Short Worked Example **Problem**: A small watershed receives a 2-hour rainfall event. The discharge measurements at the outlet are recorded as follows: | Time (hours) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | |--------------|---|---|---|---|---|---|---|---|---| | Discharge (m³/s) | 2 | 3 | 8 | 15 | 12 | 7 | 4 | 3 | 2 | **Task**: Identify the key features of the hydrograph. **Solution**: - **Base flow** = 2 m³/s (initial steady discharge before rainfall) - **Rising limb** = Hours 0-3 (discharge increases from 2 to 15 m³/s) - **Peak discharge** = 15 m³/s at hour 3 - **Falling/recession limb** = Hours 3-8 (discharge decreases back to base flow) - **Lag time** = ~3 hours (time from rainfall start to peak) This hydrograph shows a typical flashy response with a sharp peak, indicating quick runoff—common in small or urbanized watersheds.