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HARMONS FLOODSWHY ?

Presented by: Lawrence Barrett

Engineering HydrologistWater Resources Authority

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Location Map of Harmons

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History of Flooding in Harmons

1916/17Saturday March 10, 1917, Gleaner reports on “Government’s Answer to Mr. Esson’s Questions Relative to the Harmons Lake and Suffering it has caused to the People in the District”

1933Verbal report of flooding (No documented record available to the WRA at this time)

Historical record show high total annual rainfall in 1933

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2005

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History of Flooding in Harmons

2002

Flooding in 2002 was due to a Weather System in May and back-to-back Tropical Storms Isidore and Lili in September of the same year.

Approximate area inundated ~ 0.44km2 (44 hectares) (109acres)

Maximum depth of inundation ~ 3m (10ft) (does not consider depth of mined areas)

Volume of water in storage ~ 1.1 - 1.32 Mm3 (300 – 350 Mgal)

Flood duration ~ 5.5months

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Current FloodingCurrent flooding is associated with Hurricanes Dennis & Emily in July 2005 and Hurricane Wilma in October 2005

Water levels rising since September/October 2005

Current levels have exceeded the 2002 peak water level

Current rate of rise ~ 0.003m/d (0.01ft/d) (0.12in/day)

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Comparing 2002 & 2005 Floods

 2002

(Peak Levels)2005

(Still Rising)

Cause

•Weather System in May-02•Tropical Storms Isidore & Lili in

Sep-02

•Hurricanes Dennis & Emily in Jul-05

•Hurricane Wilma in Oct-05

Area inundated~ 0.44km2 (44ha) ~ 0.60km2 (60ha)

Depth of inundation ~ 2 - 3m (6 -10ft)  ~ 3 - 4.6m (10 - 15ft)

Volume of water in storage

~ 1.32Mm3

 ~ 2.6Mm3

Flood Duration ~ 5.5 months > 5.5 months

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Factors Influencing the Flooding

Four factors influencing the flooding:

1. Topographic Influence

1. Geological Influence

1. Rainfall & Antecedent Influence

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Topographic InfluenceThe communities of Harmons and Porus (Redberry included) are situated in depressions

Lowest contoured elevation at Harmons ~ 168m amsl (550ft amsl)

Lowest contoured elevation at Porus ~ 137m amsl (450ft amsl)

Groundwater flow is slowed in these depressions due to low/flat hydraulic gradients (slope of the water table) of the water surface in these topographically low areas

The Water ponds, rises and expresses itself as springs generating large surface flows

Surface flows through Redberry Community (Nov-05) ~ 113,000m3/day (US 30 Mgal/day)

Surface flow - Milk River @ Scotts Pass (Nov-05) ~ 746,000m 3/day (US 197 Mgal/day)

Milk River flow show increase of 167m3/day over pre Hurricanes Dennis & Emily Flow

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Topography & Groundwater Profile

Pre Hurricanes Dennis & Emily Levels

(1)

Post Hurricane Wilma Water Level

Peak Water Level in Content

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Geological InfluenceHydrostratigraphy

The entire region from Mile Gully to Harmons is underlain by the White Limestone Formation which is classified as an aquifer

Aquifer

Subterranean layer of porous water-bearing rock, gravel, or sand capable of storing

and conveying water to wells and streams (Draft National Water Resources Master Plan for Jamaica)

Faulting

A series of NW-SE trending faults, referred to as the Williamsfield Trough, extends from Mile Gully in northern Manchester, through Porus and down to the St. Toolies Area

The Williamsfield Trough serves as a preferential flow path for groundwater out of the Manchester Highlands

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Whitney Fault

Queen Town Hill Fault

Groundwater Flow Direction

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Rainfall & Antecedent Influence

Recharge (inflow into the aquifer)

Rainfall recharges the aquifer which maintain wells and streams

Extreme rainfall results in high recharge to the aquifer

The high recharge results in a net inflow into the aquifer which results in the rising of the groundwater table

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Rainfall & Antecedent Influence(Recharge to the Aquifer)

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Content #4 (m) Russel Place (m)

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Rainfall & Antecedent Influence

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Westher System (May-02) (10days)T/Storms Isadore & Lili (Sep-02) (14days)Hurricanes Dennis & Emily (Jul-05) (5days)Hurricane Wilma (Oct-05) (7days)

Grove Place Manchester PasturesWINDALCO -Kirkvine

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Rainfall & Antecedent Influence

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Grove Place Manchester PasturesWINDALCO -Kirkvine

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Plot of Water Levels-June 2002 to August 2003

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417914215642522428874325243617439834434845809461744690537073374383853439995410914255243647462043746940026425834513911171400574151844075466311120237165375303789538261397224081743739459313719639753423094486647058390524307037624376313763837645376523765937666376733768037687376943770137708377153772237728377363774337750377573777037778377923780637820378333784837862Content BH Melrose BH Porus Hope

" Note peaks from May/June rains on Melrose plot

" Note peaks of September water levels moving from north to south like a wave of water through the aquifer.

" Note small change in reservoir area vs recharge area

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Projected Time for WL to Crest

Water Level to crest at the end of January 2005 ± 1 Week

Projected timeframe based on travel time of the wave in the 2002 flood event from the peak water level in Content to the peak water level in Harmons

Date of crest water level in content – Oct 4, 2002

Date of crest water level in Harmons – Jan 3, 2003

Travel time ~ 3 months

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Impacts on CommunityElectricity and water supply disrupted

Entire community of John Robinson now without power

Inundation of access roads

Risk to health and wellbeing of the community

Disruption of livelihood and loss of income

Persons have to evacuate their homes with the possibility that the have to pay rent

Some small businesses depend on the electricity to operate

The threat to life

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Recommendations

Zoning of the community for residential and non-residential purposes

New Access Roads (Temporary & Permanent)

Rehabilitation of mined areas by the Mining Companies

Restricting access to mined depression when the water recedes by fencing

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