CN1548665A - Reasonable exploitation of fresh water lens body in coral reef island - Google Patents

Abstract

The present invention is the reasonable exploitation technology of fresh water lens body in coral reef island. The technology includes determining the specific shape and water storing amount of the fresh water lens body, determining the allowed exploitation amount and deciding the exploitation strength of the fresh water lens body. The said technology provides accurate and reliable data for the exploitation of the fresh water resource to ensure the safety of fresh water lens body and long term safe utilization of the fresh water resource in coral reef island.

Description

The rational exploitation technology of coral reef island fresh water lens

Technical field

The present invention relates to the production technique of a kind of coral reef island fresh groundwater.

Technical background

Many coral reefs island that distributing, marine site, China South Sea, because the restriction of hydrogeological conditions, the overwhelming majority does not have freshwater resources capable of direct drinking on these islands.For many years, the army and the people stationed on the island and naval vessel water all lean on remote the conveying, and fortune water cost is very high.The army and the people's water on the present island, except that collecting, storing the rainwater, utilizing the fresh water of storing under the face of land is one of main approach.The water table on coral reef island is through forming year in year out.The coral reef island is distributed in tropical marine site and the ocean surface of warm current process is arranged, rainfall is abundant, and the part rainwater permeates the ground by floor debris, grit and soil and forms the fresh water water body, is that central thick rim is thin because of there is form in it, as if one piece of convex lens, so be called fresh water lens.

Fresh water lens on the coral reef island is most valuable freshwater resources, does not have tangible interface between lens and the seawater, and the intermediate zone of broad is arranged.The variable thickness of fresh water lens on the different islands and reefs.The factor that influences fresh water lens size and water quality comprises natural cause and human factor.Natural cause comprises the vegetation state etc. on hydrogeological characteristics, island size, amount of precipitation, morning and evening tides and the island on island.For example, fresh water lens forms than being easier under the geological conditions of the unconsolidated grit sedimentary deposit of no secondary pore growing; Amount of precipitation causes the fresh water lens atrophy owing to the covering amount reduces in less season; The width on island just can not form fresh water lens etc. during less than 270 meters.Human factor mainly contains intensity, method and the position of groundwater abstraction and islander's production and living condition etc.Well is the intake strucure of the groundwater abstraction used always, and when extracting water with well, if it is excessive to extract intensity, the WIH head sharply reduces, and the seawater of lens bottom will rise, and just might puncture lens, and makes lens destruction.Particularly when water intake well just in time was positioned on the crack, the excessive intensity of drawing water can make seawater along rising on the crack, and a lens is divided into two little lenies, and the reserves of fresh water can significantly reduce.The division of this lens is difficult to recover often.For this reason, seek a kind of coral reef island underground fresh-water resource to be carried out the rational exploitation utilization,, seem very important to guarantee the method for coral reef island fresh water lens safety.

Summary of the invention

The rational exploitation technology that the purpose of this invention is to provide a kind of coral reef island fresh water lens, determining the shape and the fresh water reserves of fresh water lens more exactly, with and the yield and the mining rate that allow, to guarantee the safety of coral reef island fresh water lens.

The rational exploitation technology of coral reef of the present invention island fresh water lens comprises following method:

A, determine the concrete shape and the moisture storage capacity of fresh water lens

Plan view according to the coral reef island, set up rectangular coordinate system xoy, with two bunches respectively the line segment of parallel coordinates ox and coordinate oy be divided into the coral reef island latticed, the per unit grid length of side is respectively Δ x, Δ y, and the numbering of each grid is expressed as (i, j) with its grid number on x, y direction, and wherein i is the numbering number of x direction, and j is the numbering number of y direction, then

The fresh water lens surface exceeds the elevation on sea level on each grid $h_{f,i,j}=\sqrt{H_{i,j}}$

The fresh water saline interface is at the degree of depth h of b.s.l. on each grid _{S, i, j}=α h _{F, i, j}

Wherein:

${H^{n+1}}_{i,j}=\frac{1}{\mathrm{\&omega;}+\frac{a^2\mathrm{\&mu;}}{4\mathrm{k\&Delta;t}\sqrt{{H^N}_{i,j}}}}[\mathrm{\&omega;}{{\stackrel{\&OverBar;}{H}}^{n+1}}_{i,j}+(1-\mathrm{\&omega;})({{\stackrel{\&OverBar;}{H}}^n}_{i,j}-{H^n}_{i,j})+\frac{{H^n}_{i,\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="A0311785900101.png"\; state="\{\{state\}\}">j</figure-callout>}}}{4\mathrm{k\&Delta;t}\sqrt{{H^n}_{i,j}}}+\frac{a^2{\mathrm{\&epsiv;}}_{i,j}}{2k(1+\mathrm{\&alpha;})}$

Subscript i in the formula, j represents the value of the capable j row of i grid, subscript n and n+1 represent the value of n and n+1 time horizon respectively.

ε _{I, j}Be that (arrangement etc. comprises rainfall, evaporates and draw water for i, the j) increment on the last unit area.

$\mathrm{\&alpha;}=\frac{{\mathrm{\&gamma;}}_f}{{\mathrm{\&gamma;}}_s-{\mathrm{\&gamma;}}_f}$

K---transmission coefficient

μ---specific yield

ω is a weight coefficient, 0≤ω≤1

Δ t---time step

Δ x, Δ y---space step-length

The pondage of fresh water lens $V=\mathrm{\&mu;}\underset{i}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}\mathrm{\&Delta;}{x}_i\mathrm{\&Delta;}{y}_j(1+\mathrm{\&alpha;})h_{f,i,j}$

B, determine the permission yield of fresh water lens

The permission yield Q of fresh water lens _k＜Q _b-(Q _Zf+ Q _Zt)

Wherein: Q _bBe fresh water lens annual recharge, Q _ZfBe the evaporation from phreatic water amount on coral reef island, Q _ZtVegetation transpiration rate for the coral reef island;

C, determine the mining rate of fresh water lens

The mining rate Q of fresh water lens＜2kr _oh _f

Wherein: r _oBe the radius of well, k is a transmission coefficient;

D, according to the result of calculation of above-mentioned each method, carry out the selection of dry point and determining of year fresh water yield and mining rate.

The concrete shape of fresh water lens of the present invention and the Mathematical Modeling of moisture storage capacity, can calculate the concrete shape and the moisture storage capacity of coral reef island fresh water lens more exactly, thereby can determine the thickness of a certain position, coral reef island fresh water aquifer more exactly, the fixed point addressing of exploiting point for fresh water provides reference frame accurately and reliably; The permission yield and the mining rate of fresh water lens also can be gone out by calculated with mathematical model of the present invention more exactly simultaneously, thereby the formulation and the water intaking rationally that can be the annual fresh water plan in coral reef island yield provide reference accurately and reliably, avoid the blindness exhaustive exploitation of underground fresh-water resource, guaranteed the safety of coral reef island fresh water lens, made on the island the army and the people be able to long-term security ground and use underground fresh-water resource.

Description of drawings

Now in conjunction with the accompanying drawings this is described in further detail clearly.

Fig. 1 is fresh water lens computing grid figure in island, Yongxing in the Xisha Islands;

Fig. 2 is the bathymetric chart of its fresh water lens;

Fig. 3 is the 3-D view of its fresh water lens sea level with top;

Fig. 4 is the 3-D view of its fresh water lens b.s.l. part.

The specific embodiment

As shown in Figures 1 to 4, be example with island, Yongxing in the Xisha Islands, the rational exploitation technology of this coral reef island fresh water lens comprises following method:

A, determine the concrete shape and the moisture storage capacity of fresh water lens

Plan view according to the coral reef island, set up rectangular coordinate system xoy, with two bunches respectively the line segment of parallel coordinates ox and coordinate oy be divided into the coral reef island latticed, the per unit grid length of side is respectively Δ x, Δ y, and Δ x=Δ y, and the numbering of each grid is expressed as (i, j) with its grid number on x, y direction, wherein i is the numbering number of x direction, j is the numbering number of y direction, then

The fresh water lens surface exceeds the elevation on sea level on each grid $h_{f,i,j}=\sqrt{H_{i,j}}$

The fresh water saline interface is at the degree of depth h of b.s.l. on each grid _{S, i, j}=α h _{F, i, j}

Wherein:

${H^{n+1}}_{i,j}=\frac{1}{\mathrm{\&omega;}+\frac{a^2\mathrm{\&mu;}}{4\mathrm{k\&Delta;t}\sqrt{{H^N}_{i,j}}}}[\mathrm{\&omega;}{{\stackrel{\&OverBar;}{H}}^{n+1}}_{i,j}+(1-\mathrm{\&omega;})({{\stackrel{\&OverBar;}{H}}^n}_{i,j}-{H^n}_{i,j})+\frac{{H^n}_{i,\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="A0311785900101.png"\; state="\{\{state\}\}">j</figure-callout>}}}{4\mathrm{k\&Delta;t}\sqrt{{H^n}_{i,j}}}+\frac{a^2{\mathrm{\&epsiv;}}_{i,j}}{2k(1+\mathrm{\&alpha;})}$

Subscript i in the formula, j represents the value of the capable j row of i grid, subscript n and n+1 represent the value of n and n+1 time horizon respectively.

ε _{I, j}Be that (arrangement etc. comprises rainfall, evaporates and draw water for i, the j) increment on the last unit area.

$\mathrm{\&alpha;}=\frac{{\mathrm{\&gamma;}}_f}{{\mathrm{\&gamma;}}_s-{\mathrm{\&gamma;}}_f}$

K---transmission coefficient

μ---specific yield

ω is a weight coefficient, 0≤ω≤1

Δ t---time step

Δ x, Δ y---space step-length

The pondage of fresh water lens $V=\mathrm{\&mu;}\underset{i}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}\mathrm{\&Delta;}{x}_i\mathrm{\&Delta;}{y}_j(1+\mathrm{\&alpha;})h_{f,i,j}$

The above formula of each data substitution can be drawn the calculated value V=3 of the pondage of island, Yongxing fresh water lens, 300,000m ³

B, determine the permission yield of fresh water lens

The permission yield Q of fresh water lens _k＜Q _b-(Q _Zf+ Q _Zt)

Increment Q _b: generally calculate increment by annual rainfall.As increment by 2.5mm/d, the supply water yield Q of lens acquisition in a year _b=(2.5/1000) * 365 * 1.8 * 10 ⁶=1642500m ³

Evaporation capacity Q _Zf: the groundwater evaporation amount depends on factors such as weather conditions, soil layer property, depth of groundwater table.In the evaporation process, many factors such as temperature, wind speed, sunshine, humidity, rainfall intensity, crop growth period and the soil layer capillary tube conveyance power of water that changes with the diving buried depth all are labile state again.Generally can determine,, can determine according to the data in condition of similarity area if do not have according to the data of locality.

As according to spreading all over the statistics of the 45 mouthfuls of wells in island, Yongxing, its bury of groundwater is 1.60m, and year evaporation capacity is by 60mm, then Zheng Fa water yield Q _ZfFor:

Q _zf＝(60/1000)×1.8×10 ⁶＝108000m ³

Transpiration rate Q _Zt: plant absorbs moisture via root system in growth course, and the process of losing by blade face evaporation ease claims blade face evaporation (transpiration).Transpiration rate calculates can be with reference to following table

Difference plant year transpiration rate summary value

Botanical name	Year transpiration rate (mm)
		Grass and cultivated plant	????229-254
Big broad-leaved plant	????203-305
		Little tree and shrub	????154-203
Coniferous tree	????102-154

As the situation according to island, Yongxing, Xisha, selecting its year transpiration rate is 203mm.Transpiration rate Q so ₃For:

Q _zt＝(203/1000)×1.8×10 ⁶＝365400m ³

According to balanced principle, the annual in theory water yield Q that can extract _TFor:

Q _T＝Q _b-(Q _zf+Q _zt)＝1642500-(108000+365400)＝1169100m ³

Actual yield Q _kShould satisfy formula: Q _k＜1169100m ³

Claims (1)

1, the rational exploitation technology of a kind of coral reef island fresh water lens is characterized in that comprising following method:

A, determine the concrete shape and the moisture storage capacity of fresh water lens

Plan view according to the coral reef island, set up rectangular coordinate system xoy, with two bunches respectively the line segment of parallel coordinates ox and coordinate oy be divided into the coral reef island latticed, the per unit grid length of side is respectively Δ x, Δ y, and the numbering of each grid is expressed as (i, j) with its grid number on x, y direction, and wherein i is the numbering number of x direction, and j is the numbering number of y direction, then, the fresh water lens surface exceeds the elevation on sea level on each grid $h_{f,i,j}=\sqrt{H_{i,j}}$ The fresh water saline interface is at the degree of depth h of b.s.l. on each grid _{S, i, j}=α h _{F, i, j}

Wherein:

${H^{n+1}}_{i,j}=\frac{1}{\mathrm{\&omega;}+\frac{a^2\mathrm{\&mu;}}{4\mathrm{k\&Delta;t}\sqrt{{H^N}_{i,j}}}}[\mathrm{\&omega;}{{\stackrel{\&OverBar;}{H}}^{n+1}}_{i,j}+(1-\mathrm{\&omega;})({{\stackrel{\&OverBar;}{H}}^n}_{i,j}-{H^n}_{i,j})+\frac{{H^n}_{i,j}}{4\mathrm{k\&Delta;t}\sqrt{{H^n}_{i,j}}}+\frac{a^2{\mathrm{\&epsiv;}}_{i,j}}{2k(1+\mathrm{\&alpha;})}$

Subscript i in the formula, j represents the value of the capable j row of i grid, subscript n and n+1 represent the value of n and n+1 time horizon respectively.

ε _{I, j}Be that (arrangement etc. comprises rainfall, evaporates and draw water for i, the j) increment on the last unit area.

$\mathrm{\&alpha;}=\frac{{\mathrm{\&gamma;}}_f}{{\mathrm{\&gamma;}}_s-{\mathrm{\&gamma;}}_f}$

K---transmission coefficient

μ---specific yield

ω is a weight coefficient, 0≤ω≤1

Δ t---time step

Δ x, Δ y---space step-length

The pondage of fresh water lens $V=\mathrm{\&mu;}\underset{i}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}\mathrm{\&Delta;}{x}_i\mathrm{\&Delta;}{y}_i(1+\mathrm{\&alpha;})h_{f,i,j}$

B, determine the permission yield of fresh water lens

The permission yield Q of fresh water lens _k＜Q _b-(Q _Zf+ Q _Zt)

Wherein: Q _bBe fresh water lens annual recharge, Q _ZfBe the evaporation from phreatic water amount on coral reef island, Q _ZtVegetation transpiration rate for the coral reef island;

C, determine the mining rate of fresh water lens

The mining rate Q of fresh water lens＜2kr _oh _f

Wherein: r _oBe the radius of well, k is a transmission coefficient;

D, according to the result of calculation of above-mentioned each method, carry out the selection of dry point and determining of year fresh water yield and mining rate.

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