Measuring Flow gauging stations. Streamflow. Hydrographs. Rating Curves: stage to discharge

Transcription

1 Streamflow Meauring Flow gauging tation Outline: Hydrograph Dicharge (Q) Flood frequency Flow calculation Rating Curve: tage to dicharge Hydrograph Hydrograph illutrate how treamflow change with time. They can demontrate repone to precipitation a well a the effect of urbanization. Daily and longer hydrograph provide a picture of baeflow, torm flow, and nowmelt. Average annual treamflow graph provide a picture of water reource variability. 4 Shape of the treamflow hydrograph from an individual torm Water Year Hydrograph Snowmelt Flow rate 2500 Streamflow (c cf) Storm flow 0 8/12 10/1 11/20 1/9 2/28 4/19 6/8 7/28 9/16 Date Source: pratt/image/hydrograph.gi Time Baeflow 5 6 1

2 What i dicharge? Dicharge: The volume of water that flow pat a certain point in a tream over a pecific period of time a.k.a FLOW = volume/time To olve flow you need: area (ft 2 ) & velocity (ft/) or time () & volume (ft ) How do we calculate dicharge or flow (aka Q)? What we have: area (ft 2 ) & velocity (ft/) time () & volume (ft ) How do we ue thee variable to get Q? 2 Q = Area ( ft ) Velocity OR Volume ( ft ) Q = Time ( ) 7 8 Streamflow Cro Section Important Flow Unit for water Cro-Section Area (ft 2 ): Width of tream (ft) x depth of tream (ft) Streamflow velocity (f/) 2 Q = Area ( ft ) Velocity cf (ft /) cubic feet per econd Often ued for treamflow gpcd gallon per capita per day Reidential ue of water per peron, per day gal/min gallon per minute Flow rate for houehold fixture (hower, faucet, etc.) af/year acre feet per year (72,400 af/yr = 100 cf) Amount of water for irrigation, water utilitie & many quantified water right cm (m /) cubic meter per econd (1 cm = 5. cf) Alo ued for treamflow 9 10 Daily Hydrograph Rillito Streamflow Flow rate Storm flow Baeflow Time

3 Sabino Creek gauge height San Pedro River 1 14 Sabino Creek annual treamflow Green River Salt River, Arizona Colorado River 15,000 cf cf 17 18

4 Miiippi River at Baton Rouge Flood Freq: What i a 100 year Flood? pic2.city-data.com/picthumb/thumbv10142.jpg 619,000 cf The maximum level of flood water or flow that occur, on average, once every 100 year. It eem imple, but What i the probability that a 100 year flood will occur in any given year? 1% chance of a 100 year flood every year 100% % = 1 100year yr year and 500 year flood? 100% % 100% % = 10 = year yr 500 year yr Stationarity i Dead, Milly et al. Stationarity: the idea that natural ytem fluctuate within an unchanging envelope of variability. What ele beide climate might affect thi aumption? Probability denity function, tochatic model, GCM, LC/LU change, infratructure adequacy, time erie analyi What i the problem with thi tatitical method? IPCC model predicted runoff change by 2050 from Science, Feb Change in normal Flood Freq. from Recurrence Interval

5 Flood Probabilitie don t incorporate Waterhed Change! What change in a waterhed can affect the frequency and/or intenity of flood? Land Ue Change Human Activitie Land Cover Change Natural Waterhed Alteration Fire, cropping Change in Infratructure Building, Diverion 25 Land Ue Change Vegetation removal Increae runoff & eroion Land cover change Shrub land to graland Foret to graland Foret fire Increae runoff & eroion SWH (5), Neary 26 Human Influence and Impact Land ue change affect hydrograph Urbanization create imperviou urface, leading to increaed runoff and frequency of flood. Le water infiltrate More water enter tream Velocity increae Diverion, regulation, damming, channelization, etc. change treamflow Eroion increae impair water quality Calculating Flow (1) Flow variable Thee problem are imilar to rate type problem where velocity i the rate. How long would it take to fill an Olympic wimming pool (~400, gal) if all you had wa a garden hoe (~5 gal/min)? How do we olve thi problem? What are our variable? Know: Volume? Minute Which h equation? 2 Q = Area ft Velocity ( ) ft OR Volume( ft ) Q = Time( )

6 Flow Example (1) How long would it take to fill an Olympic wimming pool (~400,000 gal) if all you had wa a garden hoe (~5 gal/min)? gal Volume( gal) Q = min Time(min) 5gal ( gal) Q = min time(min) Calculating Flow (2) How much water can a ditch carry per month if it cro ectional area i 10 m 2 and the flow rate i 1 m/ec? How do we olve thi problem? Time() = 80,000 min = 55.5 day 1 2 Flow variable Flow Example (2) What are our variable? Know: Area, rate? flow Which h equation? 2 Q = Area ft Velocity ( ) ft OR Volume( ft ) Q = Time( ) How much water can a ditch carry per month if it cro-ectional area i 10 m 2 and the flow rate i 1 m/ec? m 2 m Q = Area m Velocity ( ) m 2 m Q = 10( m ) 1 Flow(cm) = 10 m / 4 River Comparion Area Area Length length dicharge dicharge river mi km 2 mi km cf cm Amazon 2,270,000 5,879,920 6,07 6,54, ,000 Miiippi 1,247,000,20,870 6, ,9 17,545 Colorado 246, ,450 2, 15, Salt 5,824 15, Verde 6,