A STUDY OF CONCURRENT RAINFALL-RUNOFF IN AUSTIN, TX

rose marie klee

problem

Tailwater assumptions Magnitude of concurrent events Waller Creek Tunnel Project

problem

Tailwater Elevation

problem

problem

problem

Background

Available guidance Waller Creek and Colorado River basins Areal Reduction Factors

background

background

background

methodology

Obtained Colorado River HMS model from LCRA

Computed ARFs Used GIS to create/compute circular

storm and calculate an aggregate ARF for each subbasin

Used HMS to model multiple storms in the Colorado River Basin

Evaluated results

methodology

methodology

methodology

area (mi2) radius (mi) ARF - Asquith991 0.6 0.947

10 1.8 0.89430 3.1 0.78650 4.0 0.76175 4.9 0.741

100 5.6 0.728150 6.9 0.708225 8.5 0.688300 9.8 0.671450 12.0 0.647675 14.7 0.621

1000 17.8 0.5931500 21.9 0.5602250 26.8 0.5243000 30.9 0.4954000 35.7 0.4635000 39.9 0.4386000 43.7 0.4187000 47.2 0.403

methodology

methodology

results

hydrologic element

drainage area (mi2)

time of peak

(hh:mm)

AL-27 28.62 14:05

   peak discharge

(cfs)volume

(in)volume (ac-ft)

100-yr SCS storm over all basins 23,602 7.51 11,467no ARFs over select basins 23,488 7.50 11,450

ARFs over select basins 18,711 5.84 8,908

change in:peak

discharge (cfs)

peak discharge

(%)

volume (in)

volume (ac-ft)

volume (%)

4,778 20.3% 1.66 2,542 22.2%

results

peak

discharge (cfs)

volume (in)

volume (ac-ft)

change in:peak

discharge (cfs)

volume (in)

volume (ac-ft)

no ARFs over select basins avg 37,697 1.263 28,619 26,023 0.729 18,415ARFs over select basins 11,673 0.535 10,204no ARFs over select basins max 620,040 8.930 637,221 456,334 5.720 395,434ARFs over select basins 163,706 5.840 241,787

results

eventpeak

discharge (cfs)

volume (in)

volume (ac-ft)

100-yr (no ARF) 23,488 7.50 11,450

100-yr (w/ARF) 18,710 5.84 8,908

50-yr (no ARF) 20,142 6.33 9,663

25-yr (no ARF) 17,055 5.27 8,044

hydrologic element

drainage area (mi2)

time of peak

(hh:mm)

AL-27 28.62 14:05

conclusions

Not the whole story…storms move; hydrograph timing is important.

Further work could include: elliptical storms, different reduction factors, moving storms, inclusion of hydraulic model, analysis of real storms.