Hydrology: Discharge, Hydrographs, Floods, and Sediment Transport

1. Hydrology: Discharge, Hydrographs, Floods, and Sediment Transport Unit 1: Module 4, Lecture 2

2. Objectives • Students will be able to: • interpret hydrographs. • explain the effects of urbanization on storm hydrographs. • describe factors that influence overland flow of water. • describe patterns of deposition based on particle size in a stream bed. • explain how sediment load is related to discharge.

3. Hydrology • Exhibits wide variation across watersheds • Related to • Precipitation • Geology (including topography) • Landuse & land cover • Hydrology is one of the primary factors influencing the physical and biological characteristics of streams

4. modified from www.usda.gov/stream_restoration/chap1.html Figure 1.18 Discharge • Q - Volume of water passing a point per unit time. • Q=VA or WDV

5. www.aquatic.uoguelph.ca/rivers/chphys.htm Discharge and hydrographs

6. Annual hydrographs

7. Figure 1.14 www.usda.gov/stream_restoration/chap1.html Storm hydrograph

8. Figure 1.15 http://www.usda.gov/stream_restoration/Images/scrhimage/chap1/fig1-15.jpg Effects of urbanization on a storm hydrograph

9. Fig. - 2.10 www.usda.gov/stream_restoration/chap1.html Flow paths

10. Overland flow • Occurs when soils are • saturated (after snow melt or heavy rain) • have low permeability (e.g., clay) • Strongly influenced by landform and land use • Coarse textured glacial deposits are highly permeable; bedrock & ancient lake bottoms are impermeable or have low permeability • Impervious surfaces (parking lots, structures) create impervious surfaces; • Forest harvest practices and agricultural practices affect stream flow

11. www.mmsd.com/stormwaterweb/Volume1B.htm Overland flow and development

12. We tend to have a biased view of floods as unpredictable, disastrous events, while in reality they are predictable and necessary occurrences. How does impervious surface affect the likelihood of flooding? www.aquatic.uoguelph.ca/rivers/chphys.htm Flooding

13. Flood probabilities • Recurrence interval • “1 in 100 year flood” • = probability of 0.01 or 1% • Also referred to as the recurrence interval • Defined as P = 1 / T, where: • P = Flood probability • T = Recurrence interval

14. www.aquatic.uoguelph.ca/rivers/chphys.htm Human influence on floods • Rapid runoff into channelized streams increase flood frequency and enhance downstream peaks in flood hydrographs.

15. Sediment transport

16. Current Direction Bed load particles moving by saltation Stream Bed earthsci.org/teacher/basicgeol/stream/stream.html#Erosion%20by%20Streams Sediment transport

17. The transportation of materials

18. Forms and directions of erosion by running water. H = headward erosion V = vertical erosion L = lateral erosion www.aquatic.uoguelph.ca/rivers/chphys.htm Erosion

19. Fig. - 7.23 Fig. - 7.28 Erosion in action

20. Deposition resulting in multiplechannels Deposition within a single channel aquatic.uoguelph.ca/rivers/chphys.htm aquatic.uoguelph.ca/rivers/chphys.htm Deposition

21. www.usd.edu/esci/figures/158401.JPG Sediment deposition and current velocity

22. Fig. - 8.58 www.usda.gov/stream_restoration/chap1.html Sediment load increases with discharge

23. Variation in sediment transport

24. State of the Minnesota River: Summary of Results 2000 and 2001 (Mn River Basin Data Center) Landuse/seasonal affects on sediment delivery to the Minnesota River • 2001 Minnesota River at St. Peter, MN daily average flow and tss samples (draft)

25. As discharge increases: Channel Width increases Channel Depth increases Mean velocity is stable Bed Material size decreases Slope decreases Sediment storage increases www.usda.gov/stream_restoration/chap1.html Fig. - 1.28r Longitudinal profile of a river