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

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s2 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 U1-m4-s3 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 U1-m4-s4  Q - Volume of water passing a point per unit time.  Q=VA or WDV modified from Figure 1.18 Discharge

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s5 Discharge and hydrographs

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s6 Annual hydrographs

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s Storm hydrograph

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s8 Figure 1.15 Effects of urbanization on a storm hydrograph

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s9 Flow paths Fig

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s10 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 U1-m4-s11 Overland flow and development

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s12 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?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s13 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 U1-m4-s14  Rapid runoff into channelized streams increase flood frequency and enhance downstream peaks in flood hydrographs. Human influence on floods

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s15 Sediment transport

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s16 Sediment transport earthsci.org/teacher/basicgeol/stream/stream.html#Erosion%20by%20Streams Current Direction Bed load particles moving by saltation Stream Bed

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s17 CategoryDia (mm)Wentworth scale Boulder Cobble > 256< -8 Large Small PebbleLarge Small GravelCoarse Medium Small SandVery Coarse Coarse Medium Fine Very Fine Silt< 0.063> 5 The transportation of materials

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s18 Erosion Forms and directions of erosion by running water. H = headward erosion V = vertical erosion L = lateral erosion

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s19 Erosion in action Fig Fig

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s20  Deposition resulting in multiple channels  Deposition within a single channel aquatic.uoguelph.ca/rivers/chphys.htm Deposition aquatic.uoguelph.ca/rivers/chphys.htm

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s21 Sediment deposition and current velocity

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s22 Sediment load increases with discharge Fig

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s23 Variation in sediment transport

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s24  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) Landuse/seasonal affects on sediment delivery to the Minnesota River

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s25 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 Fig r