Water-Supply Monitoring & Indicators

NJ Water Supply Advisory CouncilOctober 2, 2015

Jeffrey L. HoffmanNJDEP - NJGWS

What is a Drought?

There are 4 different types of droughts.

1. Meterological DroughtPrecipitation is less than normal

for longer than normal.

2. Hydrologic DroughtReservoirs, streamflows & groundwater levels are lower than normal for longer than normal.

Concerns about ecological impacts.

3. Agricultural Droughtevapotranspiration > precipitation at a time when plants need water.

4. Water-Supply Droughts (Socioeconomic)

“… a water supply shortage of a dimension which endangers the public health, safety, or welfare in all or any part of the State…

N.J.S.A. 58:1A-4.a.

NJDEP’s Drought of Concern

6 Regions

• Water-supply droughts may not affect all of NJ in same way.

• NJ divided into regions based on similar water-supply.

• Evaluate conditions in each region.

• Use municipal boundaries to help local officials apply water restrictions if they become necessary.

Watch Warnings Emergencies Comment

-- -- mid-1960’s Drought of record for NJ

-- -- 9/12/80 - 4/27/82Started in northeastern NJ and

expanded to central and northern Delaware basin

-- -- 4/17/85 - 3/24/86 Northeastern NJ

-- 8/2/95-9/12/95 9/13/95 - 11/3/95 Northeastern NJ

-- 12/14/98 - 2/2/99 --Northeastern NJ (ended by record

rains in Jan '99)

-- 8/2/99 – 7/17/008/5/99 - 9/14/998/5/99 - 9/27/99

Southern NJNorthern NJ

(Hurricane Floyd, Sept '99)

10/31/01-3/21/03 1/24/02 – 3/21/03 3/4/02 – 3/21/03Some regions entered and left drought

status slightly earlier.

9/13/05 - 10/14/055/8/06 – 7/3/06

9/8/10 – 10/26/10-- --

Entire state in watch each time. Ended by statewide precipitation

events.

9/23/15 - NE, C, CN regions

Relative Resource Importance to NJ Water Supply

Reservoirs Unconfined Region NJ DRBC Rivers groundwater

Northwest

Central

Northeast

Southwest

Coastal North

Coastal South

Major Source Minor Source Not a Regional Source

Regional Indicators• Development started after 1999 events – two dry

periods that could have been recognized as a single longer one.

• Wanted a better way to summarize regional hydrologic conditions.

• Need to concisely convey information to decision makers & the public.

• Designed to be updated quickly using real-time data.

• Indicators, not triggers.

Regional Indicators

• reservoirs (NJ & NY)

• groundwater levels

• streamflow

• precipitation

Reservoir Indicator

compare current storage to rule curve.

Evaluation criteria based on a frequency analysis of a running 90-

day deviation from normal.Rockaway R. above Reservoir - Flows

-250

0

250

500

750

1,000

1,250

1,500

1,750

2,000

1/05 2/05 3/05 4/05 5/05 6/05 7/05 8/05 9/05 10/05 11/05

Ob

serv

ed F

low

s (m

gd

)

daily surplus/deficit observed daily flow avg daily flow

Rockaway R. above Reservoir - deficits

-10,000

-8,000

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

8,000

10,000

12,000

1/05 2/05 3/05 4/05 5/05 6/05 7/05 8/05 9/05 10/05 11/05

Ob

serv

ed

Flo

ws

90-day surplus/deficit 50% exceedence

30% exceedence 10% exceedence

Streamflow Indicator

Groundwater Indicator

Evaluation criteria is based

on deviation from normal.

Precipitation Indicator

Original

Get 90-day surplus/deficit from MARFAC.

Mentally overlay drought regions

and make a judgement call.

Precipitation Indicator

New ~2009

Download GIS coverage of 90-day % of normal

precipitation from AHPS.

Clip to drought regions.

Calculate average % of normal in each region.

2015 Change in evaluation criterion of the AHPS % of normal precipitation

• Precipitation indicator based

on % of normal wasn’t as

useful as it should have

been in evaluating water-

supply droughts.

• Change to a frequency

analysis.

• Percentages calibrated to

past water-supply droughts.

• Will revise if not useful

enough.

Current Status

9/27/15

www.njdrought.org

Drinking-Water-Supply Status

• DEP staff look at hydrologic indicators and make a recommendation.

• DEP Commissioner has authority to declare watch & warning.

• The Governor declares a drought emergency.• This is an evaluation of a water-supply

(socioeconomic) drought.

Monitoring is always behind the curve.

“We welcome the first clear day after a rainy spell. Rainless days

continue for a time and we are pleased to have a long spell of such

fine weather. It keeps on and we are a little worried. A few days

more and we are really in trouble. The first rainless day in a spell of

fine weather contributes as much to the drought as the last, but no

one knows how serious it will be until the last dry day is gone and

the rains have come again.”

I.R. Tannehill, Drought: Its Causes and Effects, Princeton University

Press, Princeton, New Jersey, 1947

What’s Next?