Hydrology for Nutrient Management Joshua W. Faulkner, PhD WVU-Extension Fundamentals of Nutrient Management Training Course December 16-17, 2009 *Portions Adapted from Barbara Broxterman, 2005

Outline 1.Introduction to hydrologic cycle 2.Components of the hydrologic cycle 3.Agriculture, hydrology, and water quality

Why is this important? The transport of land/air applied fertilizers/animal waste products by surface or sub-surface water directly affects the health of our water quality and eco-systems. Understanding hydrology is critical to the proper planning and preparation of a comprehensive nutrient management plan..

Basic Concept of Hydrology Conservation of mass In – Out +/- Storage = 0 Water balance Precip. – ET +/- Storage – Outflow = 0 Watershed as a ‘bucket’ Simply define terms at various temporal and spatial scales.

The Hydrologic Cycle Movement of water in solid, liquid, and gas phases, on, above, or below the earth’s surface

Hydrologic Cycle Components 1.Precipitation 2.Infiltration 3.Runoff 4.Percolation 5.Evapotranspiration

Precipitation  Precipitation characteristics: -amount (in) -intensity (in/hr) -type (snow vs. rain) -areal distribution -seasonality

Precipitation (cont’d): Hydrologic Frequency Analysis  Useful for engineering design and understanding likelihood of storm events occurring  Analyze 30 years of hydrologic records for precipitation intensity, duration, and depth  Return period: Time within which depth and duration of a storm will occur at least once on the average  For example: conservation/storage structure design (animal waste lagoon design based on 25-yr, 24-hr storm)

Precipitation (cont’d) 25-year, 24-hr storm

Precipitation (cont’d): Higher Resolution for Changing Climatic Averages

NOAA Precipitation Frequency Data Server

Infiltration  Passage of water into the soil surface  Factors affecting infiltration: -precipitation duration & intensity -soil type -slope -soil moisture content -ground cover

Infiltration (cont’d) Rainfall rate vs. infiltration rate Infiltration rate decreases as soil becomes wetter Time to ponding indicates when water is available for runoff

Infiltration (cont’d) Soil texture impact on infiltration rate Infiltration rate lower in finer soils Infiltration rate is greater when soil is well structured (large, connected pores)

Infiltration (cont’d) Ground cover impact on infiltration rate Ground cover affects surface condition, resulting in more gradual decline in infiltration rate, and less runoff Infiltration rates in old permanent pasture can be 7 times higher than in bare, crusted ground

Runoff  Portion of the precipitation that makes it way towards stream channel, lakes, etc.  Simply, portion of precipitation that does not evaporate or infiltrate

Runoff (cont’d)  Factors affecting runoff: -Precipitation duration & intensity (rate exceeds soils infiltration capability) -Watershed characteristics (size, shape, soil, soil moisture content, topography, geology, ground cover, landuse, man-made changes)  In general, factors that enhance infiltration reduce runoff

Runoff (cont’d): Watershed Factors  Hydrologic Soil Group (HSG)  Group A – Low Runoff Potential: Sand, loamy sand or sandy loam types of soils. High infiltration rates even when thoroughly wetted. Consist chiefly of deep, well to excessively drained sands or gravels and have a high rate of water transmission.  Group B – Moderately Low Runoff Potential: Silt loam or loam. It has a moderate infiltration rate when thoroughly wetted and consists chiefly or moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures.  Group C – Moderately High Runoff Potential: Sandy clay loam. They have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine structure.  Group D – Highest Runoff Potential: Clay loam, silty clay loam, sandy clay, silty clay or clay. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface and shallow soils over nearly impervious material.

Runoff (cont’d): Watershed Factors Soil Moisture Status Characterized by Antecedent Moisture Condition (AMC) by NRCS for runoff volume design Based on 5-day antecedent rainfall & season Greater AMC, greater chance of runoff 5-day antecedent rainfall (mm) during AMCDescriptionDormant SeasonGrowing Season IOptimum<13<36 IIAverage IIIRecent heavy rain or cool temps >28>58

Runoff (cont’d): Watershed Factors  Land-use  Runoff volumes increase with greater percentage of impervious area in watershed  Management and variations within land- use type also impact runoff volumes  For example, NRCS-CN is an empirically determined metric that is chosen based on land-use to predict runoff

Runoff (cont’d): Watershed Factors Runoff Curve Numbers Land use, crop, and management Hydrologic soil group ABCD CULTIVATED, with crop rotations Row crop, poor management Row crop, conservation mgmt. Small grain, poor mgmt. Small grain, conservation mgmt. Meadow PASTURE, permanent w/moderate grazing WOODS, permanent, mature, no grazing Source: National Engineering Handbook, USDA-NRCS, Hydrology Sec. 4, 1972

Percolation  Vertical movement of water through soil profile  Deep percolation: Movement of water beyond the reach of plant roots (i.e., groundwater recharge)  Factors affecting percolation: -soil properties -moisture content -layering -geology

Percolation (cont’d): Field Scale

Percolation (cont’d): Soil Water

Percolation (cont’d): Groundwater Interactions

Evapotranspiration (ET)  ET: Evaporation from bare soil, open water, and plant surfaces plus transpiration by plants  Dependent upon:  Vegetation type  Vegetation density  Solar radiation  Soil Moisture  Wind and relative humidity

Evapotranspiration (ET) (cont’d)  ET Prediction  Mass transfer Requires measurements of wind and humidity  Energy balance Requires measurements of temperature and humidity  Combination of mass and energy methods  Pan Evaporation Straightforward, but requires Class A Evaporation Pan measurements

Evapotranspiration (cont’d) ET range in WV – in/year

Agriculture, Hydrology, and Water Quality  Three factors impact likelihood of water pollution from agriculture: -Availability -Detachment -Transport  Water movement is drives pollution

In Summary: Remembering the ‘bucket’… What water goes in, must come out What impacts how and when that water comes out? What does that water interact with during that cycle?