Chapter 6: Hydrologic Processes and Watershed Response

Purpose of the Course: To provide learners with knowledge and skills in hydrology and its application in forestry, watershed management and environmental management.

Water Resources Research, 1979

Evaporation from a large hardwood forest is estimated from measurements of the required meteorological variables and from measured stomatal resistances. A correction factor is derived to overcome the incorrect assumption that evaporative demand remains the same during wet and dry periods. The factor is based on the ratio of the isothermal resistances during the wet and subsequent dry periods. The stomatal measurements were converted to canopy resistances by dividing by the leaf area index and were used to obtain the water balance for the entire season. The results are analyzed to show that evaporation from a wet canopy is often 2-3 times greater than transpiration from the same surface. Rates of interceptionai loss, calculated from the wet and dry evaporation rates, were verified by direct measurements of throughfall and stemflow. Net interceptional loss, equal to the excess evaporation from a wet canopy over a dry one, depended on rainfall duration and character and was on the average about 60-80% of total interception, In the overall summer water balance of 442 mm of precipitation and 52-mm depletion of soil storage, transpiration via the trees accounted for 261 mm; evaporation from the wetted leaves and branches for 111 mm, and runoff for 131 mm, giving an error of closure in the water balance of only 9 mm. If transpiration only had been used instead of interception when the canopy was wet, the error in the water balance would have been 100 mm. INTRODUCTION At present there is much controversy regarding the effect of intercepted rainfall on the water balance of forested watersheds. The core of the argument is whether rain retained by vegetation represents a total loss or no loss of moisture beyond the normal evapotranspiration of the canopy. The dis-' agreement stems largely from the way in which intercepted rainfall is viewed. If it is considered as a reduction in rainfall reaching the ground, then it could indeed be a total loss. This early view was shared by hydrologists who looked at interception only in terms of the inputs of the hydrologic cycle. But if the water cycle of the entire soil-vegetation complex is considered, then intercepted rainfall is not a total loss, because when the foliage is wetted, transpirational withdrawal of soil moisture is reduced. The magnitude of transpirational saving during the evaporation of intercepted rainfall is therefore critical in determining how much of a moisture loss interception constitutes. If the rate of water loss is the same whether the vegetation is wet or dry, then it matters little whether evaporative demand is satisfied by intercepted water or soil moisture. Burgy and Pomeroy [1958] found that in vigorously growing laboratory grass plots the evaporation of a given amount of intercepted water (sprinkled on the plots) corresponded to an almost equal reduction in the amount of transpiration from the plants, in that total moisture loss was approximately the same for plots with wetted and dry leaf surfaces. Field studies by McMillan and Burgy [1960] on short, clipped grass in California gave similar results. The early ideas, based on these experiments, maintained that since a given supply of energy will evaporate only a given amount of water, then the evaporation of the moisture retained by the foliage must be compensated for by an equal reduction in transpiration. If, on the other hand, evaporation of intercepted rainfall is Copyright ¸ 1979 by the American Geophysical Union.

Introduction: Water can occur in three physical phases: solid, liquid, and gas and is found in nature in all these phases in large quantities. Depending upon the environment of the place of occurrence, water can quickly change its phase. The hydrological cycle is a model used to describe the different stages water goes through during its journey from the oceans to the atmosphere, onto the land and back to the oceans. According to National Research Council (NRC, 1982), " The hydrological cycle is the pathway of water as it moves in its various phases to the atmosphere, to the earth, over and through the land, to the ocean and back to the atmosphere".

Forest hydrology: processes, management and assessment, 2000

• SFMN archives Background: • SFMN archives Back Cover: • SFMN archives 65 Appendices 67 1 Forest planning and operational practices to promote the conservation of water resources: a survey of current practices and operations guidelines 77 2 Provincial and Federal guidelines used to assess degree of policy adherence to hydrological principles List of Boxes Box 1. Department of Fisheries and Ocean's Environmental Process Modernization Plan includes Operational Statements designed to streamline the review and approval process of management activities Box 2. Operational Statements to be met for ice bridges and snow fills in order to avoid a full DFO review Box 3. British Columbia leads in the adoption of a results-based approach to forest management Box 4. The importance of maintaining soil properties during forest operations HYDROLOGICAL PRINCIPLES FOR CONSERVATION OF WATER RESOURCES WITHIN A CHANGING FORESTED LANDSCAPE | IRENA CREED ET AL. 2011 A STATE OF KNOWLEDGE REPORT | SUSTAINABLE FOREST MANAGEMENT NETWORK Principle 2. Conserve critical hydrological features by minimizing disturbance to areas involved in the source, movement and storage of water. Management Action 2A: Minimize disturbance to soils, especially within or near areas that focus the recharge of water into subsurface pathways. Management Action 2B: Minimize disturbance in filter areas around streams, wetlands and lakes, and other sensitive sites (required buffer width will depend on dominant hydrological processes in given locale to maintain water quality of receiving water bodies). Management Action 2C: Minimize disturbance to storage areas (such as wetlands and ephemeral saturated areas). Principle 3. Maintain connections between hydrological features by minimizing disruptions to water, sediment and nutrient flows. Management Action 3A: Consider the interconnectedness and interdependence of water pathways through watersheds when developing management plans (i.e., look beyond the forest stand and consider where the stand occurs with respect to the watershed and water flows). Management Action 3B: Locate roads, bridges, culverts and harvest areas to ensure surface and subsurface hydrological connectivity is maintained and flow is neither impeded nor enhanced.

2011

Earth System Dynamics, 2014

The contribution of land evaporation to local and remote precipitation (i.e. moisture recycling) is of significant importance to sustain water resources and ecosystems. But how important are different evaporation components in sustaining precipitation? This is the first paper to present moisture recycling metrics for partitioned evaporation. In the companion paper Wang-Erlandsson et al. (2014) (hereafter Part 1), evaporation was partitioned into vegetation interception, floor interception, soil moisture evaporation and open-water evaporation (constituting the direct, purely physical fluxes, largely dominated by interception), and transpiration (delayed, biophysical flux). Here, we track these components forward as well as backward in time. We also include age tracers to study the atmospheric residence times of these evaporation components. We present a new image of the global hydrological cycle that includes quantification of partitioned evaporation and moisture recycling as well as the atmospheric residence times of all fluxes. We demonstrate that evaporated interception is more likely to return as precipitation on land than transpired water. On average, direct evaporation (essentially interception) is found to have an atmospheric residence time of 8 days, while transpiration typically resides for 9 days in the atmosphere. The process scale over which evaporation recycles is more local for interception compared to transpiration; thus interception generally precipitates closer to its evaporative source than transpiration, which is particularly pronounced outside the tropics. We conclude that interception mainly works as an intensifier of the local hydrological cycle during wet spells and wet seasons. On the other hand, transpiration remains active during dry spells and dry seasons and is transported over much larger distances downwind, where it can act as a significant source of moisture. Thus, as various land-use types can differ considerably in their partitioning between interception and transpiration, our results stress that land-use changes (e.g. forest-to-cropland conversion) do not only affect the magnitude of moisture recycling, but could also influence the moisture recycling patterns and lead to a redistribution of water resources. As such, this research highlights that land-use changes can have complex effects on the atmospheric branch of the hydrological cycle.

South-east European forestry, 2017

Background and Purpose: Water in forest ecosystems can be present in various forms. The hydrological water cycle unfolds via fundamental hydrological processes such as evapotranspiration, precipitation, infiltration and outflow. Certain infrastructure works and recent climate changes within lowland forest areas have resulted in changes in flood water and ground water trends, and in quantities of precipitation and evapotranspiration. One of the chemical water quality indicators is the presence of metals in water. Higher metal concentrations in natural waters are undesirable since they are polluters of aquatic systems and detrimental to living organisms. Particularly dangerous are cadmium and lead. The objective of this paper was to analyse watercourse levels, ground water depths, and relations between precipitation waters, flood waters, ground waters, relative air humidity and evapotranspiration. An additional objective was to analyse the pollution of precipitation and flood waters in lowland forest ecosystems. Materials and Methods: The study was conducted in the Posavina region in Croatia. Precipitation data from Nova Gradiška meteorological station, watercourse levels of the Sava River and ground water depth data from piezometer stations were used in the analysis of the hydrological relations. For water quality analysis, precipitation was collected at six sample sites during the spring of 2015 and 2016. Flood water and precipitation were collected in three repetitions during the spring of 2015 and 2016. Results: Trends of the Sava River water levels and ground water levels dropped significantly. The precipitation volume trend in the study area was positive, but not statistically significant, while evapotranspiration amounts increased significantly. Conclusions: A significant correlation has been found between particular water forms in the hydrological cycle, i.e. between precipitation waters, flood waters and ground waters, and between relative air humidity and evapotranspiration. No pollution of precipitation waters and flood waters with metals was found.