Questions and Definitions from Last Week 10 minutes – work individually 5 minutes – discuss in small teams 5 minutes – discuss with the whole group
What is the average annual rainfall in Los Angeles? 15 inches What’s the least amount of rain we’ve had on record? <5 inches What’s the most amount of rain we’ve had on record? ~38 inches When does it rain in Los Angeles? Most rain occurs from November to April Why is it important to understand rainfall seasonality and variability? To plan for water supply and flood control
Water Balance Equation – write the equation and define each of the terms Precipitation = ET + GW + Runoff Precipitation = rain, snow, sleet, hail, etc. ET = Evapotranspiration = the process by which water is transferred from land to the atmosphere by evaporation from soil and other surfaces and by transpiration from plants (evaporation of water from plant leaves) Groundwater storage = water that is stored in deep underground in soil pores or rock crevices Runoff = water that flows over the land surface and in creeks, streams, and rivers
Define Infiltration – the process by which water enters the soil surface and moves downward Define Percolation - the movement of water through the soil. Once rainwater infiltrates, it can either be evaporated, transpired, or percolated deeper into the soil to recharge groundwater.
Watershed – the area draining to a specific point on a stream is called the watershed for the stream to that point. Often, the point is where the stream (or creek or river) reaches the ocean or meets a larger stream, but a watershed can be delineated to any point on a stream.
Give 2 reasons why is it important to be able to delineate a watershed? If you want to know where pollution in a stream is be coming from, you need to know the area that drains to it, then you look at the land uses (residential, urban, industrial, agricultural) in that watershed. You have to know the area of the watershed (acres or square miles) to calculate the water balance and estimate streamflow for water supply and flood planning.
Urban Runoff Video – 5min http://www.surfrider.org/coastal- blog/entry/great-student-urban-runoff- videos
OPEN SPACE Pervious surfaces Lots of vegetation Fewer pollutants Natural drainage network Most rain infiltrates into the soil Natural streams with vegetation URBAN Impervious surfaces Not much vegetation More pollutants Dense storm drain network (concentrated flows) Most rain flow directly to streams Concrete stream channels with little/no vegetation
Pervious surface: allows water to infiltrated Impervious surface: does not allow water to infiltrate Concentrated flow: deep, fast flow of water in channels or gullies (opposite of shallow, slower flow across a flat surface)
Urban Watershed Scavenger Hunt on Jefferson High School Campus (40 minutes, two teams)