Hydrology in Watershed

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1 Setting the Course for Improved Water Quality Hydrology in Watershed Systems Photo by Don Berger Minnesota Pollution Control Agency Session 5A: A TMDL training gprogram for local government leaders and other water resource managers wq-iw3-55a

2 Hydrology is one of many disciplines involved in TMDL studies Biology Water chemistry Social sciences

3 In this presentation Basic principles i of hydrology Sources and pathways of flow in watersheds Importance of hydrology to TMDL studies and water quality management

4 Watersheds integrate physical, chemical, biological i l processes A watershed is an area of land that drains to a common point TMDL studies use watersheds as the biophysical basis for water quality planning and management Watersheds integrate physical, chemical and biological processes

5 Minnesota Pollution Control Agency This module focuses on watershed hydrology

6 What is hydrology? The study of water in all its forms (liquid, gas, and solid) on, in and over the land areas of the earth Michigan DEQ Hydrology is important at a global, regional or watershed scale

7 Hydrologic processes affect water quality The movement of surface and groundwater results in the transport and delivery of pollutants to waterbodies

8 Minnesota Pollution Control Agency The hydrologic cycle c/o US EPA

9 Why is hydrology important to TMDL studies? Before we can manage an impaired waterbody, we must understand watershed hydrology Hydrology is critical to understanding the sources and movement of water (and pollutants) to a waterbody Addressing water quality problems in water bodies will require addressing hydrologic pathways (i.e. reducing surface runoff, increasing infiltration, etc.)

10 Pollution esota P Minne Sources of water affecting stream flow Precipitation is the major source of new water in watersheds Each watershed also stores existing water

11 Types of precipitation contributing water to watersheds rainfall drizzle snow sleet hail fog dew frost

12 Precipitation affects the amount timing distribution quality of water moving through a watershed

13 Humans cannot control precipitation They can control land use decisions and human activities that can change how much precipitation is intercepted and stored in watersheds

14 Water storage and movement A watershed is essentially an enormous precipitation collecting, storing and routing device Storage and movement of water within watersheds involves a complex combination of many smaller processes Infiltration and storage of precipitation minimizes surface runoff and reduce the movement of pollutants to streams

15 Water storage on earth can be natural or man-made Depression storage Soil water Vegetation any natural or man-made surface where water collects and either seeps or evaporates (lakes, wetlands, ponds, reservoirs, etc.) water held within the soil used by plants Groundwater saturated t zone (aquifers) Channel storage water held within the channel (stream, river, ditch) Adapted from Peter Block, 2002

16 Water movement in a watershed The pathways for precipitation, from rainfall to stream flow, involves a combination of surface and sub-surface processes Difficult to separate the various pathways of flow Water can move between sources (source interactions)

17 Hydrologic pathways in a watershed Evapotranspiration Precipitation Water table Surface runoff Groundwater or base flow Channel interception Channel storage (stream flow) Infiltration & subsurface flow Adapted from Kenneth Brooks, et. al., 2003

18 Ground water recharge and discharge zones in watersheds Recharge Discharge the process of water soaking into the ground to replenish ground water aquifers a process by which subsurface water becomes surface water

19 Groundwater recharge zones within a watershed Recharge occurs in specific areas of a watershed The nature and timing of recharge depends on excessive water infiltration and percolation beyond plant roots

20 Minnesota Pollution Control Agency Groundwater recharge and discharge zones c/o USGS

21 Groundwater discharge zones in a watershed Time needed for water to move from recharge zones to discharge points can be minutes to years Groundwater discharging to surface waters is mostly unseen, but if observed, is typically seen as springs or seeps Groundwater discharges to surface waters can greatly affect temperature, dissolved oxygen and other characteristics of water which can affect aquatic life

22 Drainage systems may impact the recharge of some deep aquifers lake Subsurface tile drainage Deep aquifer

23 Minnesota Pollution Control Agency Surface / groundwater interactions in watersheds

24 Surface water / groundwater interactions ti Ground and surface water are often treated as separate systems however, they are inextricably They should linked be studied as an integrated system

25 Surface water / groundwater interactions ti Pathways of the interaction are complex Interactions are neither constant, nor consistently separate Groundwater is the major source of base flow in many Minnesota streams

26 Groundwater / surface water interactions can result in gaining i or losing stream reaches Gaining stream reach Losing stream reach Water table Groundwater Water table

27 Wetlands are an expression of ground- water and surface water interactions ti Pollution esota P Minne Photo: BWSR Photo: NRCS Photo: BWSR

28 Wetlands with unusual groundwater interactions ti Bogs Perched water table Regional water table c/o Scott County Ground water rich in calcium carbonate Fens

29 Summary Hydrology concerns water in all its forms on, in and over the land areas of the earth The hydrologic cycle feeds flow in our streams, ultimately affecting water quality Water storage and movement involves a complex combination of many processes

30 Summary Specific areas within a watershed serve as recharge and discharge zones Surface water in lakes, streams and wetlands interacts with groundwater By understanding di hydrologic pathways, we can influence water quantity and quality

31 Now what? Now we understand the importance of hydrology in watershed management. What do we do with that knowledge? Use the following modules and worksheets to help you scope and plan your project. j

32 What s next? Future modules will address other disciplines related to watershed management: Water chemistry Biology (watershed assessment: land use, land cover, geography, soils, etc.)

33 Final thought A watch is complicated, but a watershed is complex. Remove one gear from the thousands in a watch and it, predictably, stops working. Pollute one river and the whole watershed is likely to shift and change in a thousand ways, but nobody can be quite sure if or when a toxic algal bloom will appear in the lake. - Dr. Judith Van Houten University of Vermont