____________________________________________________SITES 2005.1.4SITES 2005.1.4

INTEGRATED DEVELOPMENT ENVIRONMENTINTEGRATED DEVELOPMENT ENVIRONMENTfor

WATER RESOURCE SITE ANALYSIS

COMPLEX WATERSHEDSCOMPLEX WATERSHEDSSITES IN SERIESSITES IN SERIES

OBJECTIVES

• Understand concepts related to dam design with complex watersheds

• Discuss stream reach routing options

UPPER

LOWER

UPPER

LOWER

Dams in Series

• Policy - Dams in series are to be given special consideration (NEM-210 520.24)

• NEM-210 520.27(b)(2)(i) breach considerations.

Upper DamUpper Dam• Hydrologic criteria and procedures (TR-60)

– same as or more conservative than those for downstream dams - if failure of the upper dam could contribute to the failure of the lower dam

– If routing through an upper dam and it is overtopped it is to be considered breached.

– Dam breach criteria TR -60 p 1-1

Complex WatershedsComplex Watersheds

• Hydrologically homogeneous W/S

• Soil and Cover

• Size

Complex WatershedsComplex Watersheds

• Drainage areas above 25 square miles should be subdivided.

• Goal - Hydrologically Homogeneous Areas

• Drainage areas more than 10 square miles should be considered for subdivision.

Upstream SiteUpstream Site

• Homogeneous or Subdivided -- assumed to be in place for the design of the lower site.

• Site is routed only

• Spillway materials data not required.

• Minimum data can be included in structure table.

Downstream SiteDownstream Site

• Site to be designed.

• If Integrity analysis is required - then all data is required.

Sites in SeriesSites in Series

Upper DamUpper Dam

Reach

Lower Dam

The upper The upper dam is dam is considered a considered a feature of the feature of the watershed for watershed for the design of the design of the lower the lower dam.dam.

Lower DamLower Dam

• Hydrographs from upper controlled areas are based on same criteria as for lower dam.

• Flows are routed through spillways of all upper dams and channel reaches to the lower dam where they are combined with the hydrographs from any uncontrolled drainage area. The combined hydrographs are used to flood route the lower dam.

W/S DATAW/S DATA

• The hydrologic characteristics of the uncontrolled area or subarea are to be used to develop all of the required input data for the area or subarea.

• This data includes - DA, Tc, CN, stage-storage, sediment, hazard class, rainfall, Ci, Baseflow, etc.

Stream Reach Routing Options

Reach LengthReach Length

• The length of channel through which a hydrograph will be routed.

• In most cases the distance downstream from the outlet of the upstream site to the most upstream normal pool elevation of the dam downstream.

Reach 1Reach 1

Reach 2Reach 2

Upper DamUpper Dam

Lower DamLower Dam

This is an example of a reach routing where the characteristics of the channel were not the same for the whole reach. So two reaches have been used to represent the channel.

Cross Section Rating CurveCross Section Rating Curve

• The shape of the cross section with possible multiple roughness values gives stage, area, and discharge that is used to define how the hydrograph will be routed downstream.

Example of a subdivided cross Example of a subdivided cross section - note areas of multiple section - note areas of multiple roughness shown in the sections.roughness shown in the sections.

7

8

Muskingum-Cunge Reach Routing In SITES

Reach Cross Section Rating Table

• Data derived from HECRAS, Manning’s, etc.

• Reach Length = 5400 feet, Bankfull Elevation = 2422.5

ElevationDischarge

(cfs)End Area

(ft2)Top

Width (ft)Friction

Slope (ft/ft)

2410.0 0 0 0 0.00502411.4 25 19 23 0.00382412.3 50 41 31 0.00182413.4 100 81 42 0.00112415.1 250 170 60 0.00082416.9 500 296 78 0.00072418.2 750 404 90 0.00072419.3 1000 502 100 0.00082420.1 1250 592 109 0.00082420.9 1500 677 116 0.00082421.5 1750 755 123 0.00092422.1 2000 843 193 0.00092423.1 2500 1112 369 0.00102423.9 3000 1751 1440 0.00102424.4 3500 2739 1935 0.00082425.0 4000 3844 1994 0.0007

Rating TableRating Table

Fig 17-13 Convex routing Fig 17-13 Convex routing coefficient versus velocitycoefficient versus velocity

Taken from App. H in TR-20