Hydrology Discharge Hydrographs Floods and Sediment Transport Unit

Hydrology: Discharge, Hydrographs, Floods, and Sediment Transport Unit 1: Module 4, Lecture 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. Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 2

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 Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 3

Discharge · Q - Volume of water passing a point per unit time. · Q=VA or WDV Figure 1. 18 Developed by: Merrick, Richards modified from www. usda. gov/stream_restoration/chap 1. html Updated: August 2003 U 1 -m 4 -s 4

Discharge and hydrographs www. aquatic. uoguelph. ca/rivers/chphys. htm Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 5

Annual hydrographs Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 6

Storm hydrograph Figure 1. 14 www. usda. gov/stream_restoration/chap 1. html Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 7

Effects of urbanization on a storm hydrograph Figure 1. 15 Developed by: Merrick, Richards http: //www. usda. gov/stream_restoration/Images/scrhimage/chap 1/fig 1 -15. jpg Updated: August 2003 U 1 -m 4 -s 8

Flow paths Fig. - 2. 10 www. usda. gov/stream_restoration/chap 1. html Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 9

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 Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 10

Overland flow and development www. mmsd. com/stormwaterweb/Volume 1 B. htm Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 11

Flooding · 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 Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 12

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 Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 13

Human influence on floods · Rapid runoff into channelized streams increase flood frequency and enhance downstream peaks in flood hydrographs. www. aquatic. uoguelph. ca/rivers/chphys. htm Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 14

Sediment transport Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 15

Sediment transport Current Direction Bed load particles moving by saltation Stream Bed earthsci. org/teacher/basicgeol/stream. html#Erosion%20 by%20 Streams Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 16

The transportation of materials Category Boulder Cobble Dia (mm) Wentworth scale > 256 < -8 Large Small 128 - 256 64 - 128 -7 -6 Pebble Large Small 32 - 64 16 - 32 -5 -4 Gravel Coarse Medium Small 8 - 16 4 -8 2 -4 -3 -2 -1 Sand Very Coarse Medium Fine Very Fine 1 -2 0. 5 - 1 0. 25 - 0. 5 0. 125 - 0. 25 0. 063 - 0. 125 0 1 2 3 4 < 0. 063 >5 Silt Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 17

Erosion Forms and directions of erosion by running water. H = headward erosion V = vertical erosion L = lateral erosion www. aquatic. uoguelph. ca/rivers/chphys. htm Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 18

Erosion in action Fig. - 7. 23 Fig. - 7. 28 Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 19

Deposition · Deposition within a single channel aquatic. uoguelph. ca/rivers/chphys. htm Developed by: Merrick, Richards · Deposition resulting in multiple channels aquatic. uoguelph. ca/rivers/chphys. htm Updated: August 2003 U 1 -m 4 -s 20

Sediment deposition and current velocity www. usd. edu/esci/figures/158401. JPG Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 21

Sediment load increases with discharge Fig. - 8. 58 www. usda. gov/stream_restoration/chap 1. html Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 22

Variation in sediment transport Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 23

Landuse/seasonal affects on sediment delivery to the Minnesota River · 2001 Minnesota River at St. Peter, MN daily average flow and tss samples (draft) State of the Minnesota River: Summary of Results 2000 and 2001 ( Mn River Basin Data Center) Developed by: Merrick, Richards Updated: August 2003 U 1 -m 4 -s 24

Longitudinal profile of a river · 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/chap 1. html Developed by: Merrick, Richards Updated: August 2003 Fig. - 1. 28 r U 1 -m 4 -s 25