NWS-COMET Hydrometeorology Course 9 – 24 May 2000

1. NWS-COMET Hydrometeorology Course9 – 24 May 2000 Hydrology Primer Presented by Dennis Johnson Tuesday & Wednesday 9-10 May 2000

2. Dennis L. Johnson, Asst. ProfessorJuniata CollegeEnvironmental Science & Studies1700 Moore StreetHuntingdon, PA 16652Phone: (814) 641-5335Fax: (814) 641-3685johnson@juniata.eduhttp://www.juniata.edu/~johnson

3. Purpose of the Hydrometeorology Course • Increase the participants knowledge and understanding of the interaction between meteorology and hydrology in watersheds: • Increase participants understanding of the functional aspects of watersheds; • Enhance the participants knowledge of the capabilities, limitations, and applications of new hydrometeorological observing systems; • Improve the participants ability to identify significant mesoscale meteorological events and to produce Quantitative Precipitation Forecasts; • Increase participants understanding of the effectiveness of the NWS forecast and warning methodologies and plan future enhancements; and • Build awareness of the need for close ties between RFC's and WFO's.

4. Purpose of the PRIMER • Provide an introduction between participants & establish backgrounds. • Introduce participants to basic terminology and concepts of hydrologic forecasting that will be used throughout the hydrology portion of the COMET Hydromet course. The primer introduces these concepts and specific detail will be provided in week 3. • Establish the course objectives as per the expectations of the participants. • Establish hydrologic concerns in the various participants' regions.

5. In the end, it is intended that participants will understand the hydrologic forecast process, the assumptions in the process, and the responsibilities associated with interpreting and issuing the forecast.

6. Mission of NOAA's NWSHydrologic Services Program • To provide river and flood forecasts and warnings for protection of life and property • Provide basic hydrologic forecast information for the nation's economic and environmental well being.

7. Modernized NWS • “It is essential to emphasize the complementary aspects of operational hydrology and meteorology in the modernized NWS, while recognizing the uniqueness of RFC and WFO operations. “

8. New or Improved Products • ...the production of a variety of hydrologic forecast products for an increased number of river locations across the country, including ESP-based products

9. What is ESP?

10. What is ESP? • Ensemble Streamflow Production (ESP) • Inputs the current moisture level of soil and the precipitation from previous years into a model which produces the diagram seen above. • For example, the moisture content of today would be inputted, along with the precipitation that occurred over the next week, but 50 years ago. • This would then be repeated for 49 years ago, 48, etc., and then an average discharge based on history can be determined.

11. Hydrology … an earth science. It encompasses the occurrence, distribution, movement, and properties of the waters of the earth and their environmental relationships." (Viessman, Knapp, Lewis, & Harbaugh, 1977 - Introduction to Hydrology, Harper & Row Publishers, New York)

12. Hydrometeorology … an interdisciplinary science involving the study and analysis of the interrelationships between the atmospheric and land phases of water as it moves through the hydrologic cycle." (Hydrometeorological Service Operations for the 1990's, Office of Hydrology, National Weather Service, NOAA, 1996).

13. Hydrometeorology - Links Hydrology Engineering/Fluid Mechanics In-depth hydrologic Ø Hydrometeorology analysis Interdisciplinary Execution of complex Ø Orientation Meteorology hydrologic models. Thermodynamics/atmospheric Adjustment of Assimilation/use of Ø physics orientation model parameters, and WSR-88D based the derivation of precip. estimates In-depth meteorological Ø hydrologic forecasts for Production and/or Ø analysis all time scales use of QPF's and Weather forecast and Ø Applied hydrologic Ø other hydromet. warning operations research forecasts Climatological forecasting Ø Development and Ø Use of RFC guidance Ø Applied meteorological Ø calibration of (e.g. flash flood) in and climatological hydrologic models hydrologic warning research. Development of Ø operations Development and calibration Ø hydrologic applications Use of soil moisture Ø of meteorological models procedures. states from Development of Ø hydrologic model in meteorological applications atmospheric model and procedures. Applied Ø hydrometeorological research.

14. A Basic Review of Fluid Properties

15. Units & Properties of Water

16. Common Unit Conversions Area Volume Runoff Volume Discharge Power

17. Area • 1 acre = 43,560 ft2 • 1 mi2 = 640 acres • 1 hectare = 100m x 100m = 2.471 acres = 10,000 m2 • 1 km2 = 0.386 mi2 AreaVolume Runoff Volume Discharge Power

18. Volume • 1 acre-foot = 1 ac-ft = 1 acre of water x 1 foot deep = 43,560 x 1 = 43,560 ft3 • 1 ac-inch = 1 acre x 1 inch deep = 43,560 x 1/12 = 3,630 ft3 • 1 ft3 = 7.48 gallons • 1 gallon H2O ~ 8.34 lbs. AreaVolumeRunoff Volume Discharge Power

19. Runoff Volume • 1-inch of runoff over 1 square mile : • 1/12 feet x 1 mi2 x 640 acres/mi2 x 43,560 ft2/acre = 2,323,200 ft3 Area VolumeRunoff VolumeDischarge Power

20. Discharge • 1 cfs = 1 cubic foot per second • 1 cfs x 3600 sec/hr x 24 hrs/day = 86,400 cfs/day • 1 cfs x 7.48 gal/ft3 x 3600 sec/hr x 24 hrs/day = 646,272 gpd = 0.646 MGD • 86,400 cfs/day x 1 ac-ft/43,560 ft3 = 1.983 ac-ft/day (~ 2 ac-ft/day) • 1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs = 0.992 ac-in/hr • 1 ac-in/hr x 43,560 ft3/ac-ft x 1 hr/3600 sec x 1 ft/12 inches = 1.008 cfs Area Volume Runoff VolumeDischargePower

21. Power • 1 hp = 550 ft*lb/sec = 0.7547 kilowatts Area Volume Runoff Volume DischargePower

22. Hydrologic Cycle Topics Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs

23. Precipitation Precipitation -Snow Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • ... primary "input" for the hydrologic cycle (or hydrologic budget). • … The patterns of the precipitation are affected by large scale global patterns, mesoscale patterns, "regional" patterns, and micro-climates. • … Knowing and understanding the general, regional, and local precipitation patterns greatly aids forecasters in determining QPF values. • … In addition to the quantity of precipitation, the spatial and temporal distributions of the precipitation have considerable effects on the hydrologic response.

24. Snow Precipitation -Snow Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • ... nature of the modeling efforts that are required. • … response mechanisms of snow are at a much slower time scale than for most of the other forms of precipitation. • … The melt takes place and the runoff is "lagged" due to the physical travel processes. • … Items to consider in the snowmelt process are the current "state" of the pack and the snow water equivalent of the snow pack., as well as the melt potential of the current climate conditions. • … A rain-on-snow event may produce very high runoff rates and is often a difficult situation to predict due to the integral nature of the runoff and melt processes. The timing of these events is often very difficult to predict due to the inherent "lag" in the responses.

25. Evaporation Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … Evaporation is a process that allows water to change from its liquid phase to a vapor. • … Hydrologists are mostly interested in the evaporation from the free water surface of open water or subsurface water exposed via the capillary action; however, precipitation that is intercepted by the vegetative canopy may also be evaporated and may be a significant amount in terms of the overall hydrologic budget. • … Factors that affect evaporation are temperature, humidity and vapor pressure, radiation, and wind speed. • … A number of equations are used to estimate evaporation. There are also a number of published tables and maps providing regional estimates of annual evaporation.

26. Transpiration Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … Water may also pass to the atmosphere by being "taken up" by plants and passed on through the plant surfaces. • … Transpiration varies greatly between plants or crops, climates, and seasons. • … Evaporation and transpiration are often combined in a term - evapotranspiration. • … In many areas of the country and during certain seasons evapotranspiration is a major component of the hydrologic budget and a major concern in water supply and yield estimates.

27. Storage - Surface Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • ... Storage - Surface is used to describe the precipitation that reaches the ground surface; however, is not available for runoff or infiltration. • … It is instead, held in small quantities on the surface in areas, such as the leafy matter and small depressions. • … In general, surface storage is small and only temporary in terms of the overall hydrologic budget; however, it may have an effect on a storm response as it is effectively "filled" early on a storm event.

28. Infiltration Precipitation Evaporation Transpiration Storage-surface Infiltration -Subsurface Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … Soils, depending on current conditions, have a capacity or ability to infiltrate precipitation, allowing water to move from the surface to the subsurface. • ... "physically based” -> soil porosity, depth of soil column, saturation levels, and soil moisture. • … The infiltration capacity of the soil column is usually expressed in terms of length per time (i.e. inches per hour). • … As more water infiltrates, the infiltration generally decreases, thus the amount of water that can be infiltrated during the latter stages of a precipitation event is less than that at the beginning of the event.

29. Infiltration cont. Precipitation Evaporation Transpiration Storage-surface Infiltration -Subsurface Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs … Storms that have high intensity levels may also cause excess precipitation because the intensity (inches per hour) may exceed the current infiltration capacity (inches per hour). … periods of low rainfall or no rainfall will allow the soil to "recover" and increase the capacity to infiltrate water.… Infiltrated water replenishes soil moisture and groundwater reservoirs. Infiltrated water may also resurface to become surface flow. … attempt to account for infiltration by estimating excess precipitation (the difference between precipitation and excess being considered infiltration), for example, the Soil Conservation Service (SCS) runoff curve number method

30. Subsurface Flow Precipitation Evaporation Transpiration Storage-surface Infiltration -Subsurface Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs …water may move via several paths. …subsurface flow can be evaporated if there is a well maintained transfer mechanism to the surface. This is particularly true for areas of high ground water table (the free water surface of the groundwater) which is within the limits of the capillary action or transport abilities. …Vegetation may also transpire or use the water. …The subsurface flow may also continue to move with the groundwater table as a subsurface reservoir, which the natural system uses during periods of low precipitation.

31. Storage - Subsurface Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … The infiltrated water may continue downward in the vertical, may move through subsurface layers in a horizontal fashion, or a combination of the two directions. • … Movement through the subsurface system is much slower than the surface and thus there are storage delays. The water may also reach an aquifer, where it may be stored for a very long period of time. • … In the NWS River Forecast System (RFS), the subsurface storage is represented by imaginary zones or "tanks". These tanks release the stored water at a given or calibrated rate. The released water from the subsurface zones is added to the surface runoff for convolution with the unit hydrograph.

32. Runoff Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … runoff will be used to collectively describe the precipitation that is not directly infiltrated into the groundwater system. • … is generally characterized by overland, gully and rill, swale, and channel flows. • … is that portion of a precipitation event that "quickly" reaches the stream system. The term "quickly" is used with caution as there may be great variability in response times for various flow mechanisms. • … Runoff producing events are usually thought of as those that saturate the soil column or occur during a period when the soil is already saturated. Thus infiltration is halted or limited and excess precipitation occurs. This may also occur when the intensity rate of the precipitation is greater than the infiltration capacity.

33. Overland Flow Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs … Overland flow or surface flow is that precipitation that either fails to penetrate into the soil or that resurfaces at a later point due to subsurface conditions. … often referred to as "sheet" flow. … for the purposes of this discussion, overland flow (sheet and surface flow, as well) is considered to be the flow that has not had a chance to collect and begin to form gullies, rills, swales

34. Overland Flow (cont.) Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs … will eventually reach defined channels and the stream system. … may also be infiltrated if it reaches an area that has the infiltration capacity to do so. … Overland flow distances are rather limited in length - National Engineering Handbook (1972) - overland flow will concentrate into gullies in less than 1000 feet. … Other (Seybert, Kibler, and White 1993) recommend a distance of 100 feet or less.

35. Gullies & Rills Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs ... sheet flow or overland flow will soon concentrate into gullies and rills in the process of flowing towards the stream network. The location of these gullies and rills may vary from storm to storm, depending on storm patterns, intensities, current soil and land use conditions.

36. Swales Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs … swales are of a more constant or permanent nature. … do not vary in location from storm to storm. … Swales are a natural part of the landscape or topography that are often more apparent than gullies and rills. … Flow conditions and behaviors in swales are very close to that which is seen in channels.

37. Channel Flow Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs … Excess precipitation ultimately reaches the stream channel system. … the stream system is generally more defined, it is by no means a constant or permanent entity. … The stream bed is constantly changing and evolving via aggredation and degradation. … Stream channels convey the waters of the basin to the outlet and into the next basin. … attenuation of the runoff hydrograph takes place. … Stream channel properties (flow properties) also vary with the magnitude of the flow.

38. Stream Channels Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement -Overland flow -Gullies and Rills -Swales -Channel Flow -Stream Channels Streamflow Storage-Reservoirs … Channels are commonly broken into main channel areas and overbank areas. … overbank areas are often referred to as floodplains. … Stream gaging stations are used to determine flows based on elevations in the channel and/or floodplain. … Bank full is often thought of as flood stage although more rigorous definitions are more applicable as they pertain to human activity and potential loss of life and property. … It is worth noting that the 2-year return interval flow is often thought of as "bank-full".

39. Streamflow Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … in the public eye -> the most important aspect of flooding and hydrology. • … flooding from streams and rivers have the greatest potential to impact human property and lives; although overland flow flooding, mudslides, and landslides are often just as devastating. • … Subsurface flow also enters the stream; although in some instances and regions, stream channels lose water to the groundwater table - regardless, this must be accounted for in the modeling of the stream channel. • … Channels also offer a storage mechanism and the resulting effect is most often an attenuation of the flood hydrograph.

40. Storage - Reservoirs Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … Lakes, reservoirs, & structures, etc. are given a separate category in the discussion of the hydrologic cycle due to the potential impact on forecasting procedures and outcomes. • … provide a substantial storage mechanism and depending on the intended purpose of the structure will have varying impacts on the final hydrograph, as well as flooding levels. • … This effect can vary greatly depending on the type of reservoir, the outlet configuration, and the purpose of the reservoir.

41. Storage - Reservoirs (cont.) Precipitation Evaporation Transpiration Storage-surface Infiltration Storage - Subsurface Runoff Water Movement Streamflow Storage-Reservoirs • … Flood control dams are used to attenuate and store potentially destructive runoff events. • … Other structures may adverse effects. For example, bridges may cause additional "backwater" effects and enhance the level of flooding upstream of the bridge. • … a catastrophic failure of a structure often has devastating effects on loss of life and property.

42. NWS - Forecast Terminology

43. Hydrology Terminology Topics Watershed Stream flow Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency

44. Hydrology Terminology Watershed -drainage area -drainage basin -sub-basin -sub-area Streamflow Routing Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • A watershed is an area of land that drains to a single outlet and is separated from other watersheds by a divide. • Every watershed has a drainage area. • Related terms: drainage basin, sub-basin, sub-area.

45. Hydrology Terminology Watershed Streamflow -cross-section area -Manning’s “n” Routing Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • Streamflowis the movement of water through a channel. • Thecross-sectional areaof a stream is the region bounded by the walls of the stream and the water surface. The cross-sectional area is illustrated below. • See alsoManning’s “n”. Cross-sectional Area Stream Flow

46. Diagram 1 Diagram 2 Hydrology Terminology Watershed Streamflow -cross-section area -Manning’s “n” Routing Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • Manning’s “n”is a measure of the roughness of a surface, and in streamflow it is the roughness of the channel bottom and it’s sides. Diagram 2 will have a higher Manning’s “n” because it has rougher surface due to the jagged bottom and pebbles.

47. Routing Hydrologic Hydraulic Hydrology Terminology Watershed Streamflow Routing -Hydrologic -Hydraulic Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • Routing is used to account for storage and translation effects.

48. Hydrology Terminology Watershed Streamflow Routing -Hydrologic -Hydraulic Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency Generalized effect of routing

49. Hydrologic Routing Watershed Streamflow Routing -Hydrologic -Hydraulic Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • Hydrologic routing is the more simple of the two techniques. • Based on the continuity equation which says • Inflow - Outflow = Change in Storage - or - • A second relationship is also required which relates storage to discharge. This relationship is usually assumed, empirical, or analytical in nature. • Two types of hydrologic routing, River and Reservoir Routing.

50. Hydraulic Routing Watershed Streamflow Routing -Hydrologic -Hydraulic Reservoirs Channel Precipitation Snow Runoff Infiltration Unit hydrograph Timing Flooding Flow Grade lines Land Use Frequency • Hydraulic routing is more complex and generally considered more accurate than hydrologic routing. • Based on the simultaneous solution of the continuity equation and the momentum equation, commonly called the St. Venant equations.