Finishing Precipitation Learning Objectives Be able to construct and interpret intensity-duration-frequency graphs (P37-38) Be able to calculate area average precipitation (P39-43) CEE 3430 – Spring 2011

Intensity-Duration-Frequency IDF design curves All major cities Based on NWS data Various return periods & durations Used for drainage design of pipes & roads Used for floodplain designs - watersheds From Bedient

Design Rainfalls Design Storm from HCFCD and NWS Based on Statistical Analysis of Data 5, 10, 25, 50, 100 Year Events Various Durations of 6 to 24 hours Six Hour Rainfall From Bedient

NOAA Hydrometeorological Design Studies Center Precipitation Frequency Data Server (PFDS) http://hdsc.nws.noaa.gov/hdsc/pfds/ The standard source for design storm data CEE 3430 – Spring 2011

Example – Design Rainfall for Logan What amount of rain in Logan in a 6 hr period is a 100 yr storm What amount of rain in Logan in a 1 hr period is a 100 year storm Develop a 6 hour 100 year design storm using 1 hour time steps CEE 3430 – Spring 2011

From NOAA Atlas 14 (for Utah) CEE 3430 – Spring 2011

From NOAA Atlas 2 http://www. nws. noaa CEE 3430 – Spring 2011

From NOAA Atlas 2 http://www. nws. noaa CEE 3430 – Spring 2011

Rainfall Averaging Methods From Bedient Rainfall Averaging Methods

Thiessen Polygons - Areal Average Rainfall from Gages Connect gages with lines Form triangles as shown Create perpendicular bisectors of the triangles Each polygon is formed by lines and WS boundary P = S (Ai*Pi) / AT From Bedient

RADAR Rainfall Estimates NEXRAD provides real-time data on a ~16 km2 (6 mi2) grid Each estimate represents an average rainfall amount over the entire 4 x 4 km2 area NEXRAD rainfall estimates compare well with point rain gage measurements (r2 ~ 0.9) From Bedient

Streamflow and Hydrologic Measurements Learning Objectives Be able to describe runoff processes and components of a runoff hydrograph (p43-45) Be able to describe the impact of watershed shape and land alterations on a runoff hydrograph (p46) Be able to list ways that atmospheric parameters are measured (p47) Be able to describe how streamflow is measured and construct a rating curve (p48-54) CEE 3430 – Spring 2011

Physical Processes involved in Runoff Generation Rainfall Runoff Processes Figure 1. Physical Processes involved in Runoff Generation. Physical Processes involved in Runoff Generation

Figure 2-3

Watershed effects on hydrograph shape Figure 1-12

f1 f0 Figure 7. Rainfall, runoff, infiltration and surface storage during a natural rainstorm. The shaded areas under the rainfall graph represent precipitation falling at a rate exceeding the infiltration rate. The dark grey area represents rainfall that enters depression storage, which is filled before runoff occurs. The light grey shading represents rainfall that becomes overland flow. The initial infiltration rate is f0, and f1 is the final constant rate of infiltration approached in large storms. (from Dunne and Leopold, 1978)

Runoff Generation Mechanisms (a) Infiltration excess overland flow (also called Horton overland flow) P qo f (following Beven, 2001) See infiltration excess runoff generation animation http://hydrology.neng.usu.edu/RRP/ (ch 2)

(c) Saturation excess overland flow P Variable source area P P qo qr qs (following Beven, 2001) See saturation excess runoff generation animation http://hydrology.neng.usu.edu/RRP/ (ch 2)

Evaporation Measurement Eddy Covariance Pan Photo: http://www.campbellsci.com/documents/manuals/opecsystem.pdf

Shielded and Unshielded weighing Precip (Rain and Snow Gages Snow Pillow

Streamflow Measurement Figure 1-14

Rating Curve Figure 1-15

Summary The atmosphere is the major link between oceans and continents and drives the hydrologic cycle through precipitation Precipitation variability is summarized statistically in intensity-duration-frequency curves used for design Spatial averaging methods are used to calculate precipitation over a watershed Runoff due to precipitation involves overland flow, infiltration, interflow, the direct runoff hydrograph and baseflow Measurement methods for Precip, ET and streamflow CEE 3430 – Spring 2011