HYDROLOGY - RUNOFF

RUNOFF TOPICS

RUNOFF

RUNOFF

the draining or flowing off of precipitation from a catchment area through a surface channel. It represents the output from the catchment in a given unit of time.

1. SURFACE RUNOFF

2. GROUNDWATER RUNOFF

3. INTERFLOW/THROUGHFLOW

3 COMPONENTS OF RUNOFF

1. OVERLAND FLOW

2. CHANNEL FLOW

2 TYPES OF SURFACE RUNOFF

SURFACE RUNOFF

- is the flow of water that occurs when excess stormwater, meltwater, or other sources flow over the Earth's surface. This can happen when the soil is saturated to full capacity, excess water from rainfall or other sources cannot infiltrate into the ground, or the rate of precipitation exceeds the rate at which water can be absorbed.

OVERLAND FLOW

refers to the movement of water over the land surface, usually when the soil has become saturated, or when rainfall exceeds the infiltration capacity of the soil.

CHANNEL FLOW

Refers to the movement of water within the confines of a defined channel such as a stream, river, or canal.

GROUNDWATER RUNOFF

refers to the part of the total runoff that has infiltrated the ground, entered the saturated zone, and then re-emerged at the surface to contribute to the flow in streams, rivers, lakes, or oceans.

INTERFLOW/THROUGHFLOW

- is the lateral movement of water in the unsaturated zone of the soil, parallel to the land surface.

1. PROMPT INTERFLOW

2. DELAYED INTERFLOW

TWO TYPES OF INTERFLOWS:

PROMPT INTERFLOW

- refers to the rapid lateral movement of water in the unsaturated zone of the soil, occurring shortly after precipitation events. This quick response happens because the infiltrated water travels through preferential flow paths, such as macropores or fractures in the soil, and rapidly reaches streams or rivers. Prompt interflow contributes to streamflow within hours to days following rainfall.

DELAYED INTERFLOW

refers to the slower lateral movement of water through the soil, occurring over longer periods after precipitation events. This process happens because the infiltrated water moves through the soil matrix rather than preferential flow paths, leading to a more gradual contribution to streamflow. Delayed interflow can contribute to streamflow over days to weeks following rainfall

1. DIRECT RUNOFF

2. BASEFLOW

TWO CLASSIFICATIONS OF RUNOFF (IN TERMS OF STREAM ENTRY)

DIRECT RUNOFF

sometimes called direct stormwater runoff and stormwater runoff, is the part of the runoff which enters the stream immediately after the rainfall

BASEFLOW

- is the delayed flow that reaches a stream essentially as groundwater flow.

NATURAL FLOW (VIRGIN FLOW)

refers to the flow of a river or stream in its natural state, unaffected by human activities such as dam construction, water withdrawals, land use changes, or other alterations. This flow represents the natural hydrological conditions of a watercourse, driven solely by natural processes like precipitation, evapotranspiration, infiltration, and natural runoff.

HYDROGRAPH

is a graphical representation that shows the variation of a hydrological variable, such as streamflow or groundwater level, over time. Hydrographs typically plot the discharge (flow rate) of a river or stream against time, often in response to precipitation events.

1. RISING LIMB 2. PEAK DISCHARGE (CREST SEGMENT) 3. RECESSION LIMB (FALLING LIMB) 4. BASEFLOW 5. LAG TIME 6. TOTAL RUNOFF VOLUME

PARTS OF HYDROGRAPH

1. PERENNIAL STREAMS

2. INTERMITTENT STREAMS

3. EPHEMERAL STREAMS

TYPES OF STREAMS (ACCORDING TO ANNUAL HYDROGRAPH)

PERENNIAL STREAMS

are watercourses that flow continuously throughout the year, regardless of seasonal variations in precipitation or groundwater levels. These streams typically maintain a consistent flow rate and provide a stable aquatic habitat. Perennial streams are often fed by groundwater sources, ensuring a constant water supply even during dry periods.

INTERMITTENT STREAMS

also known as seasonal streams, are watercourses that flow periodically throughout the year, typically during wet seasons or in response to precipitation events. These streams may dry up for part of the year, especially during droughts or dry seasons, but they can exhibit flowing water during times of increased runoff or groundwater recharge.

EPHEMERAL STREAMS

also known as temporary streams, are watercourses that flow only in direct response to precipitation events, such as rainfall or snowmelt. These streams do not have a continuous flow and may remain dry for extended periods between precipitation events.

FLOW DURATION CURVE

is a graphical representation of streamflow data that illustrates the percentage of time that a given flow rate is equaled or exceeded over a specified period.

- HIGHER FLOW OCCURING TO THE LEFT AND LOWER FLOWS TO THE RIGHT

• X – AXIS: PROBABILITY OF EXCEEDENCE

• Y – AXIS: FLOW RATES

COMPONENTS OF FLOW DURATION CURVE

PROBABILITY OF EXCEEDENCE

- is a graphical representation of streamflow data that illustrates the percentage of time that a given flow rate is equaled or exceeded over a specified period.

FLOW MASS CURVE

- is a graphical representation used in hydrology to analyze the relationship between streamflow and the cumulative mass or volume of water over a specified time period. It displays the cumulative volume or mass of water flowing past a certain point in a stream over time.

• X-AXIS: TIME (DAYS/MONTHS/YEARS) • Y-AXIS: CUMULATIVE MASS OR VOLUME OF WATER PASSING A SPECIFIC POINT IN THE STREAM OVER TIME

COMPONENTS OF FLOW MASS CURVE

for analyzing the total amount of water transported by a stream or river over a given period, providing insights into the overall water yield, sediment transport, and other hydrological characteristics.APPLICATION

PURPOSE OF FLOW MASS CURVE

- Assessing total water yield from a watershed

- Estimating sediment load and transport in rivers

- Evaluating the effectiveness of reservoir operations in water storage and release

- Analyzing the impact of land use changes or climate variability on streamflow

APPLICATION OF FLOW MASS CURVE

DROUGHTS

- are prolonged periods of abnormally low precipitation and water availability, leading to water shortages and adverse impacts on agriculture, ecosystems, water resources, and society. Droughts can vary in duration, severity, and spatial extent, ranging from short-term dry spells to prolonged, multi-year drought events.

1. METEOROLOGICAL DROUGHT

2. AGRICULTURAL DROUGHT

3. HYDROLOGICAL DROUGHT

4. SOCIOECONOMIC DROUGHT

TYPES OF DROUGHTS

METEOROLOGICAL DROUGHT

A deficit in precipitation compared to the long-term average for a specific region and time period.

AGRICULTURAL DROUGHT

- A lack of soil moisture affecting crop growth and agricultural productivity.

HYDROLOGICAL DROUGHT

Reduced streamflow, groundwater levels, and water availability in rivers, lakes, and reservoirs.

SOCIOECONOMIC DROUGHT

- Impacts on human activities, such as water scarcity, food shortages, economic losses, and social disruptions.

1. NATURAL VARIABILITY

2. CLIMATE CHANGE

3. HUMAN ACTIVITIES

CAUSE OF DROUGHTS

NATURAL VARIABILITY

Climate fluctuations, such as El Niño/La Niña events and atmospheric circulation patterns.

CLIMATE CHANGE

Altered precipitation patterns and increased temperatures leading to more frequent and severe droughts

HUMAN ACTIVITIES

- Deforestation, land use changes, water overuse, and pollution affecting water availability and exacerbating drought impacts.